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Article number: 26.2.a30
https://doi.org/10.26879/1259
Copyright Paleontological Society, August 2023

The splitfin fossil species Paleocharacodon guzmanae gen. and sp. nov. is erected based on the osteological study of 14 fossil male and female specimens recovered in the Pliocene deposits of the Paleolake Amajac, in Sanctórum, Hidalgo, Mexico. This new cyprinodontiform fish exhibits the diagnostic features of the family Goodeidae and subfamily Goodeinae; like all the goodeids, its premaxilla has a straight distal end, and its premaxillary ascending process is small; and, like the goodeines, this new species was viviparous, its first anal fin ray is rudimentary, and the males show an andropodium. Although P. guzmanae displays numerous primitive features, it is not possible to place it in any of the goodeine tribes, which currently are vaguely defined by osteological features. This new species seems to be closely related to Characodon; both share a peculiar osteological character; the articular facet for the quadrate is a donut-like structure, in which the retroarticular forms the central region, and a couple of semicircular anguloarticular processes form the surrounding part. This species differs from other goodeids mainly in two features; it has a posttemporal bone with small anteroventral processes, and the openings of its supraorbital canal show the formula1-2a, 2b-3a, 3b-4a, 4b-5a, and 5b-7. The discovery of this extinct goodeid species in the great Pánuco-Salado Basin on the eastern slope of Mexican territory represents an unexpected historical element.

Carmen Caballero-Viñas. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México. Circuito de la Investigación S/N, Ciudad Universitaria, Coyoacán, Ciudad de México, 04510, Mexico.
Jesús Alvarado-Ortega. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México. Circuito de la Investigación S/N, Ciudad Universitaria, Coyoacán, Ciudad de México, 04510, México.
Kleyton Magno Cantalice Severiano. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México. Circuito de la Investigación S/N, Ciudad Universitaria, Coyoacán, Ciudad de México, 04510, México.

Keywords: new genus; new species; goodeids; Pliocene; fossil; Mexico

Final citation: Caballero-Viñas, Carmen, Alvarado-Ortega, Jesús, and Magno Cantalice Severiano, Kleyton. 2023. A Pliocene goodeid fish of the Paleolake Amajac, Sanctórum, Hidalgo, Mexico. Palaeontologia Electronica, 26(2):a30.
https://doi.org/10.26879/1259
palaeo-electronica.org/content/2023/3919-pliocene-goodeid-from-mexico

Copyright: August 2023 Paleontological Society.
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Jordan and Gilbert (1883) erected the family Goodeidae to include the “splitfins.” This group of small freshwater cyprinodontiforms fishes is endemic to the United States of America (USA) and Mexico (Doadrio and Domínguez, 2004). This family comprises two geographically disjunct subfamilies (Foster and Piller, 2018). The subfamily Empetrichthyinae consists of four living species gathered into two genera, which are oviparous and opportunistic omnivores fishes that inhabit springs and pools restricted to the south-western Great Basin of the USA (Williams and Williams, 1982). In contrast, the subfamily Goodeinae consists of about 18 genera and 44 species of viviparous fishes that have different eating habits and inhabit lakes, creeks, marshes, canals, and large rivers of the Mesa Central of Mexico and adjacent regions (Webb et al., 2004; Domínguez-Domínguez et al., 2010). The empetrichthyines, once included in the Cyprinodontidae family and now considered part of Goodeidae (Parenti, 1981), are oviparous organisms with no pelvic fins. In contrast, goodeines are viviparous, have internal fertilization, exhibit embryonic feeding by matrotrophy through trophotaeniae, and the males develop an elaborate courtship (Deacon and Williams, 1984; Doadrio and Domínguez, 2004; Domínguez-Domínguez et al., 2010). In recent studies, Goodeidae and Profundulidae are closely related (Costa, 1998; Webb et al., 2004; Nelson et al., 2016; Piller et al., 2022).

Although the origin of Goodeidae dates to the early Miocene (Foster and Piller, 2018, fig. 2), the fossil record of these fishes is relatively scarce and usually involves skeletal remains, often so fragmentary and isolated that their taxonomic identity is hardly determinable. In Mexico, fossil remains of living species have been recovered in the Neogene lacustrine and fluvial deposits scattered within the Trans-Mexican Volcanic Belt (TMVB), like those of the middle Pliocene and Plio-Pleistocene age near the Chapala and Zacoalco lakes, in the Jocotepec and Zacoalco municipalities, Jalisco, and those of Pleistocene age discovered in the Tlapacoya Municipality, Estado de Mexico (Smith, 1980; Guzmán and Polaco, 2009; Guzmán, 2015).

Up to now, only two fossil species of goodeid have been described based on complete and relatively well-preserved specimens. Empetrichthys erdisi Uyeno and Miller, 1962, is an empetrichthyine recovered from the Pliocene deposits of Santa Clara River Valley in the Piru Mountains, Ventura County, southwestern California, USA. Tapatia occidentalis Álvarez and Arriola-Longoria, 1972, is a goodeine from the Miocene lacustrine deposits at the Santa Rosa Ravin, Amatitán Municipality, Jalisco (Miller and Smith, 1986; Guzmán et al., 1998). At the beginning of this century, Becerra Martínez et al. (2002) reported complete goodeid specimens from the Pliocene strata of the Amajac Paleolake belonging to the Atotonilco El Grande Formation that outcrop in Sanctórum village within the Atotonilco El Grande Municipality, Hidalgo, central Mexico. Later, Becerra Martínez (2003) suggested the presence of two species among these fossils, an indeterminate Goodeidae and a possible member of the genus Goodea Jordan, 1880.

Despite its importance in understanding the history and composition of the North American continental fish communities, studying fossil freshwater fishes from Mexico still needs to be completed. Therefore, the authors of this work launched a project to recover and study these fossils, an effort that now has some achievements (Alvarado-Ortega and Carranza-Castañeda, 2002a-c; Alvarado-Ortega et al., 2006; Espinosa-Arrubarrena et al., 2009; Mendoza-Reynosa and Alvarado-Ortega, 2015; Mendoza-Reynosa et al., 2013). Today, we are studying the Pliocene ichthyofauna of Sanctórum; hence, the present manuscript aims to determine the taxonomical identity of that fish previously referred to as an indeterminate Goodeidae species by Becerra Martínez (2003).

The fossil goodeids studied in this work are from the lacustrine deposits of volcanic ashes and clays that outcrop within the Sanctórum village, located between the coordinates 20°18ʹ16ʺN, 98°45ʹ51ʺW (Figure 1), about 34 km northeast of the city of Pachuca (Arellano-Gil et al., 2005). The fossiliferous sequence of Sanctórum was discovered in the 1980s by Dr. Oscar Carranza Castañeda and Mr. Gerardo Álvarez Reyes, paleontologists from the Instituto de Geology (Igl) of the National Autonomous University of Mexico (UNAM). In 2008, the second of the authors of the present work began a systematic collection in a small outcrop on the outskirts of this town, called “Sanctórum-JAO site” (Figure 2), registered as a locality IGM-loc in the Colección Nacional de Paleontología at Igl-UNAM. These strata belong to the Atotonilco El Grande Formation, a lithostratigraphic unit described by Segerstrom (1961) as a sequence of clastic rocks and limestone lenses, covered or locally interspersed by basalt currents, which together are 500 to 600 m thick and were deposited into the basins of the Metztitlán and Amajac rivers.

The oldest lithostratigraphic units in the Atotonilco El Grande region are the El Doctor Formation Albian-Cenomanian limestones and the Mendez Formation Campanian-Maastrichtian marls. Such Cretaceous strata are discordantly covered by sediments of the Pachuca Group, which consists of the basal Eocene-Oligocene Amajac conglomerates that are gradually replaced by the Miocene-Pliocene strata of sandstones and silt-sandy intercalated by limonite, loamy shale, and loams. Above these lies the Pliocene-Pleistocene lacustrine and volcano-sedimentary sequence of the Atotonilco El Grande Formation. Finally, the youngest local sediments are Quaternary alluviums (Beltrán-Romero and Luna-Gómez, 1994; Kowallis et al., 1998; Salvador-Flores, 2001). The Pliocene section of the Atotonilco El Grande Formation consists of fine-grained lacustrine sediments deposited under high altitude, shallow, and low energy conditions, which allow the fossil preservation of plants, invertebrates, coprolites, and vertebrates (Arellano-Gil et al., 2005). The fossil assemblage of Sanctórum includes impressions of terrestrial and aquatic plants, charophytes, silicified wood fragments, insects, ostracods, gastropods, coprolites, frogs, salamanders, as well as a rodent jaw, a snake, and numerous fishes (Beltrán-Romero and Luna-Gómez, 1994; Velasco-de León et al., 2000; Reyes-Torres et al., 2002; Velasco-de León and Aguilar-Arellano, 2002; Zaragoza-Caballero and Velasco-de León, 2003; Palma-Ramírez et al., 2012; Avendaño Pazos, 2020; among others).

MATERIAL AND METHODS

Institutional abbreviations. The acronyms of the institutions involved with this work include CMR, Colección de Materiales Recientes (a subcollection into the Colección Nacional de Paleontología). CPUM, Colección de Peces, Universidad Michoacana de San Nicolás de Hidalgo, Michoacán. ENCB, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Ciudad de México.IGM, Colección Nacional de Paleontología, Instituto de Geología (previously Instituto Geológico de México) of the Universidad Nacional Autónoma de México, Ciudad de México. LaNaBio, Laboratorio Nacional de Biodiversidad, Instituto de Biología, UNAM. LUMIR, Laboratorio Universitario de Microtomografía de Rayos X, Centro de Geociencias of UNAM, Campus Juriquilla, Querétaro.

Preparation methods. All the fish specimens described here belong to the Colección Nacional de Paleontología. These are housed in the Museo María del Carmen Perrilliat M. belonging to the Igl-UNAM. These fossils are mechanically prepared. Under a binocular stereoscopic microscope, fine needles helped to remove the small patches of sediments and uncover the fossil osseous structures. When necessary, a solution of plexigum and methacrylate acetate, applied with fine brushes, glued hardened the fossil bones. The specimens were, directly and indirectly, observed under a stereoscopic microscope and a collection of high-quality photographs obtained in a Low Vacuum Scanning Electron Microscope (SEM). We got digital photographs with a single-lens reflex Camara (SLR) under different illumination conditions, including the natural, white, and long-wave UV (254 nm) lights, as well as with a Confocal Laser Scanning Microscope (CLSM). We obtained virtual micro-computed tomographies (μCT) of recent and fossil specimens. We generated a total of 1200 images with a voxels size of 21.86 μm of each treated fish under a protocol of 110kV, 72 μA, and 500 ms (the electronic files obtained so far will be available for further research because they will be delivered and will be part of the electronic files housed in the Colección Nacional de Paleontología). As noted below, different individuals of living species were cleared and stained according to the technique of Dingerkus and Uhler (1977). The disarticulated dry skeletons of recent goodeids included in this study were obtained by alkaline digestion when complete specimens were immersed in a saturated solution of KOH for 3 hrs and subsequently washed in clean water for 24 hrs. Bones were separated from the soft tissue debris using dissection needles under the microscope and left to dry in the shade at room temperature.

Comparative materials. CPUM donated recent females and males of 34 Mexican goodeid species are used here for comparative purposes. These specimens include Ameca splendens Miller and Fitzsimons, 1971: Complete specimens cleared and stained, CMR 1247, a male of 41.75 mm SL; CMR 1248, a female of 43.3 mm of SL. Characodon audax Smith and Miller, 1986: Complete specimens cleared and stained, CMR 1249, a male of 36.88 mm of SL; CMR 1250, a female of 37.97 mm of SL. Characodon lateralis Günter, 1866: Complete specimens cleared and stained, CMR 1251, a male of 35.83 mm of SL; CMR 1252, a female of 38.38 mm of SL. Goodea atripinnis Jordan, 1880: Disarticulated dry skeleton including CMR 1253, a male of 58 mm of SL; CMR 1254, a female of 64 mm of SL; complete specimens cleared and stained, CMR 1255, a male of 35.97 mm of SL; CMR 1256, a female of 65.74 mm of SL. Hubbsina turneri De Buen, 1940: CMR 1257, a female of 46.70 mm of SL; CMR 1258, a pregnant female of 35.08 mm of SL. Tapatia occidentalis Álvarez and Arriola-Longoria, 1972: P 3661, holotype, a complete specimen of 15.93 mm of SL (deposited in the collection of the Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional); IGM 7966, a complete specimen.

Anatomical nomenclature and abbreviations. The osteological nomenclature, abbreviations, and measurements considered in this manuscript and its figures and tables follow that of previous similar studies (e.g., Costa, 1998; Webb, 1998; Kobelkowsky, 2005).

SYSTEMATIC PALEONTOLOGY

Order Cyprinodontiformes Berg, 1940.
Family Goodeidae sensu Parenti, 1981.
Subfamily Goodeinae Jordan and Gilbert, 1883.
Tribe indeterminate
Genus Paleocharacodon gen. nov.
zoobank.org/AB23EFF9-A960-46BE-9BE6-53BB556A50C0

Species included. Paleocharacodon guzmanae sp. nov., described below.

Etymology. The genus name derives from “paleo” or “ancient” in Greek, plus “Characodon” in reference to the genus named by Günther (1886).

Diagnosis. As in the type and unique species of the genus, see below.

Holotype. IGM 13117, a complete female specimen of 37.29 mm of standard length, preserved in part and counterpart (Figure 3, Table 1).

Paratypes. IGM 13118, IGM 13119, IGM 13120 (Figure 4A), and IGM 13121 (Figure 4B) are almost complete and articulated males. IGM 13122 and IGM 13123 are incomplete and significantly disarticulated males. IGM 13124 and IGM 13125 (Figure 4C) are almost entirely well-preserved females. IGM 13126, IGM 13127, IGM 13128, IGM 13129, and IGM 13130 are incomplete specimens of unknown sex (Table 1).

Type locality and age horizon. Sanctórum-JAO site (recorded as IGM-loc 3875 in the Colección Nacional de Paleontología, Igl-UNAM), Atotonilco El Grande Municipality, Hidalgo, Mexico. Pliocene lacustrine deposits of the Paleolake Amajac belonging to the Atotonilco el Grande Formation (Figure 1 and Figure 2).

Etymology. The species epithet honors our colleague, Dr. Ana Fabiola Guzmán Camacho, who passed away in 2022, for her contributions to Mexican archaeozoology and paleoichthyology. Together the genus and species names mean “the Guzmán’s ancient Characodon fish.”

Diagnosis. Goodeinae fish with a unique combination of characters and a maximum total length is near to 60 mm, the body is elongated; slightly humped behind the head; fins rounded; pelvic fin rising at the beginning of the posterior half of the body at 57.3% of SL in males and 64.8% of SL in females, and in both cases its rear edge does not reach the anterior end of the dorsal fin base; unpaired fins opposed to each other, located far back of the body, and behind the 69% of SL; total vertebrae 35 in males including 15 abdominals plus 20 caudals while there are 31-32 in females including 14 abdominals and 17-18 caudals; anal fin rays typically 16; in males the most anterior anal rays is rudimentary and this and the following five forms the andropodium; dorsal fin rays 15 in males and 12 in females; pectoral rays 12 in males and 13-14 in females; pelvic rays 6 in both sexes; ribs 15 in males and 12-13 in females; the lateral edges of the anterior end of the parasphenoid are parallel and have no lateral wings; jaws shows a dental battery composed of a labial row of long and robust teeth distally bicuspid and acute with bases co-ossified with the bone plus smaller conic and unicuspid teeth are located lingually; the palatoquadrate arch is anteriorly inclined; the articular facet for the quadrate is donut-like with the central part formed by the retroarticular, and the surrounding region is formed by a couple of curved processes of the anguloarticular; the palatine head has an anterolateral projection; the ventroposterior end of coracoid is convex and has the posterior edge vertically tilted and notched. This species is unique in having the posttemporal with a small anteroventral process, and the openings of the supraorbital canal show the formula 1-2a, 2b-3a, 3b-4a, 4b-5a, 5b-7.

Body shape and general proportions. Table 1 shows the body measurements and proportions of Paleocharacodon guzmanae gen. and sp. nov. The fossil fishes from Sanctórum show different modes of conservation. Occasionally, their bones are totally or partially disarticulated and dispersed. Although it is common to find them relatively complete, well-articulated, and resting, showing one of the body flanks, in general, the bones of the anterior part of the head, the jaws, the nape, and the abdominal region are a little dislocated causing some imprecision in the body measurements. The present description is based on the holotype and added data observed in the paratypes. The larger specimens are the female IGM 13117 (its total and standard lengths are 48.27 and 37.29 mm) and IGM 13130, a sex-undefined and incomplete individual that may be near 100 mm of SL (not included in Table 1).

This elongated fish has a triangular head, almost as high as long, in which the snout is terminal. The maximum body height (MBH) is allometrically variable in the predorsal region of the trunk, in which the back becomes a kind of hump in the larger specimens (Table 1; Figure 3, Figure 4). Compared with females, males’ bodies and heads are shorter and lower (the SL range is 21.88-40.32 mm vs. 25.38-37.29 mm). Regarding the SL, the MBH is 16.65-22.79% vs. 28.94-35.66%; the head length is 26.66-28.01% vs. 28.77-36.12%; and the head height is 21.67-27.23% vs. 27.39-30.08%). All fins have round terminal margins. The pectoral fin extends in the first third of the abdominal region and rises between the vertebral column and the ventral edge of the body. The pelvic fin is short, located in the posterior half of the body (57.3% of SL in males and 64.8% of SL in females), and its distal ends extension does not reach the cloaca. The unpaired fins are short (concerning the SL, the dorsal fin length is 69.3% in males and 71.87% in females while the anal fin length is 70.56% in males and 73.26% in females), opposite to each other, placed on the last third of the body, and represent about 10 to 15% of SL. The caudal peduncle is robust. The caudal fin is entirely round, its base is as high as the caudal peduncle, and its shorter rays are about half its longest.

Skull. In most specimens studied here, the skull bones are so crushed or fragmented and isolated that it is difficult to recognize them accurately. Despite this situation, these exhibit the following details (Figure 5, Figure 6, Figure 7).

In the dorsal view, the skull is trapezoidal with no medial fontanels, in which the interfrontal suture is a somewhat sinuous interfrontal suture, and the frontals and supraoccipital bones are in contact separating the parietals. Anteriorly, each nasal is a flat oval bone with a large pore near its anterior that may correspond to pore 1 of the supraorbital sensory canal (Figure 6, Figure 8A). Each lateral ethmoid bone is a robust, complex C-shaped bone attached to the anterior ventral region of the respective frontal and extends up to the anterior end of the orbital part of the parasphenoid (Figure 6, Figure 7, Figure 8A).

Each frontal is laminar dorsally expanded and axe-shaped, which forms 70% of the skull length, and markedly broad in its anterior two-thirds. The surface of each frontal shows three sections or low domes joined by inconspicuous ventral ridges, in which the bone thickens (Figure 7). The medial section of the frontal is the largest, dorsally smooth, and ventrally has a series of anterior parallel longitudinal ridges in which the respective lateral ethmoid bone attaches. The lateral section of this bone is roughly triangular and displays a series of 10 large pores alongside its borders with the medial and posterior sections, which corresponds to the pores 2b, 3a, 3b, 4a, 4b, 5a, 5b, 6, and 7 of the supraorbital sensory canal (Figure 6, Figure 7). Since pores 1 and 2 of this sensory canal open in the nasal bone, the formula of these openings is 1-2a, 2b-3a, 3b-4a, 4b-5a, and 5b-7. Remarkably, the 2b of these sensory pores is complex; this opens into a broad depression in which at least two other associated pores open (Figure 7). The posterior section of the frontal is the smallest, has a triangular shape, and is behind the lateral section. Near its posteromedial limit, the lateral section has a pair of conspicuous, laminar, and parallel ridges forming a bony canal projected lateromedially, which opens dorsally, encloses pore 6, and ends right where pore 7 opens. In the most posterior part of the frontal, where this bone bends ventrally and exposes more laterally, there is a wide shallow depression that seems to be the dorsal end of the dilator fossa (Figure 6).

Each parietal is a small and smooth rectangular bone that joins the rear of the frontal and the lateral edge of the supraoccipital (Figure 6). The supraoccipital bone is an oblong, laminar, and dorsally convex bone with a large posterior crest that is bifid and expanded posteriorly (Figure 6). The basioccipital bone is triangular, anteriorly tapered, as high as its vertebral articulation, and hardly expanded laterally. In the dorsal view, the sphenotic bone is rectangular with a stout lateral process. The epiotic is a small oblong bone located in the posterior region of the skull that bears a straight posterior thick process (Figure 6).

The parasphenoid is a complex unpaired bone that is expanded laterally in its otic region, whereas its orbital part forms a rod-like structure, evenly straight. The anterior end of parasphenoid becomes dorsoventrally flat and bifid. The middle orbital section of this bone changes allometrically; in small individuals, its transversal section is “+” shaped because it has low wings expanded dorsal, ventral, and laterally whereas, in large specimens, the cross-section becomes T-shaped because the dorsal wing disappears (Figure 6, Figure 7, Figure 8A). This bone displays a triangular basipterygoid process projected dorsally and laterally at the union of its orbital and otic sections.

Otoliths. Although some specimens studied show remains of the three pairs of otoliths, only the sagittal otolith is well-preserved (Figure 8A, Figure 9, Table 2). In life, these inner ear stones are solid crystalline structures of calcium carbonate; however, the otoliths of our fossils have a grainy appearance, probably due to the partial dissolution of their calcium carbonate.

The sagittal otolith is a thick lenticular structure crudely resembling an arrowhead pointing backward, in which the ventral section is a little longer than the dorsal one (Figure 9). Its lateral surface is smooth, has a hardly protruding middle region, and peripherical concentric growth lines. On the contrary, its medial surface is irregular; it has two longitudinal grooves, one corresponding to an expanded deep concave dorsal area, and the other is a slender medial sulcus, dorsally and ventrally bordered by the cristae superior and inferior, respectively.

The contour of the sagittal otolith is slightly sinuous all around except for a conspicuous notch in the middle of the dorsal margin (Figure 9). In the rostral margin, the rostrum and antirostrum are prominent convex projections deeply separated by a very open exisura that rises from a sharp notch. In the posterior margin, the middle part is a noticeable convex process projected beyond the postrostrum and pararostrum, which are inconspicuous convex projections.

Table 2 summarizes the measurements and proportion observed in the left sagittal otolith obtained in specimen IGM 13119. This inner ear stone has 1237.1 μm of total length. Its ratio total length/maximum height is 1.36 (the maximum height is 73.3% of its total length). Its ratio ventral length/maximum heigh is 1.01 (the ventral length is 74.3% of its total length). Its relative dorsal length (DL/VL) is 98.5. Its relative medial length (ML/VL) is 1.08. Its relative antirostrum height (AH/MH) and length (AL/VL) are 0.385 and 0.099, respectively. Its relative rostrum height (RH/MH) and length (RL/VL) are 0.401 and 0.263, respectively. The exisura opens about 90°, and the posterior and postventral angles are 60 and 128°, respectively.

Circumorbital series. The circumorbital series is highly reduced and only consists of the lacrimal and dermosphenotic bones. The lacrimal bone is somewhat rectangular, about twice higher as long (Figure 5); unfortunately, none of the specimens studied here has a lacrimal that clearly shows the trajectory or the number of pores of the preorbital sensory canal. The dermosphenotic is smooth and thickened tubular bone, ventrodorsally projected, which ends with a blunt tip and borders the dorsoposterior region of the orbit. The dermosphenotic is hollow, carries the postorbital branch of the supraorbital sensory canal, and has at least four pores of that sensory canal (Figure 6).

Upper jaw. Each limb of this jaw consists of the premaxilla and the maxilla. In lateral view, the premaxilla is a sinuous bone divided into two parts. The anterior half of this bone corresponds to its toothed section, a stout bar, homogenously high, and ventrally and medially curved, in which the proximal end becomes thick, dorsally expanded, and forms a straight inter-premaxillary articular surface and a short triangular ascending process. In contrast, the untoothed section of the premaxilla is a rhomboidal-like expanded structure that includes a rectangular and flat ventral process, a short dorsal spine posteriorly projected, and a straight posterior process (Figure 6, Figure 8D, Figure 10).

The maxilla is a long, curved, untoothed bone (Figure 6A-B, Figure 7, Figure 10). In this bone, the anterior third is cylindrical, medially bent, and ends in an expanded rounded structure with two globular dorsal processes and an elongated triangular dorsal process with an acute tip. The posterior half of this bone becomes straight, flat, and broader.

In toothed elements of jaws are the premaxilla in the upper jaw and dentary in the lower jaw; these bones show two kinds of teeth, bicuspid or bifid sharp teeth and unicuspid acute teeth (Figure 6, Figure 8, Figure 10). The toothed surface of the premaxilla is broad and shows a labial or principal tooth row that consists of eight or nine bicuspid teeth that are long, thick, and have a stake-like base co-ossified with the bone. In these bifid teeth, the base is ovoid, expanded, and laterally compressed; the middle part is progressively thinner; and the terminal end becomes labio-lingually flat, broader, and divided into two symmetrical acute triangular tips with lateral slightly curved edges (Figure 11). Additionally, numerous secondary teeth are in a lingual position; these are conic, unicuspid, smaller, and shorter. Although many teeth of the principal row have the tips broken, their bases are with the dentary and premaxillary (Figure 8). Secondary teeth appear to be just tightly attached to the surface of the bone.

Lower jaw. Each limb of the lower jaw consists of four bones, the dentary, anguloarticular, retroarticular, and coronomeckelian. The dentary is a trapezoidal bone in which the coronoid process is absent, and the posterior end is expanded and deeply bifid. In this bone, the anterior and ventral edges bend medially, the ventral edge is notched, and the symphysis is straight and high (Figure 6A, Figure 8B-D, Figure 10). Here, the toothed border is straight and extended about the anterior two-thirds of this bone. The mandibular sensory canal runs alongside the ventral edge of the dentary and opens through at least four large pores; among these, the second and third pores are the most extensive and form long and wide grooves.

The anguloarticular is a small boomerang-like structure that shows limbs slightly differently shaped, forming an interior angle somewhat obtuse. This bone has a small articular process protruding in the base of its posterior edge and has a trapezoidal ventral process near its rear that sutures with the anterior border of the retroarticular (Figure 6A-C, Figure 8B, Figure 10). Here, the anterior and dorsal processes form an interior angle of about 110-120°; the anterior process has straight edges, shows an acute tip, and is about 1.3 longer, whereas the dorsal process shows somewhat convex edges and a rounded tip. This bone does not carry the mandibular sensory canal. At the base of the retroarticular articular process, the anguloarticular and retroarticular forms part of the articular facet for the quadrate. This facet is a shallow and ovoidal depression with a donut-like configuration, in which the retroarticular’s dorsal surface forms the central region of such facet, while the anguloarticular has two curved or C-shaped processes forming the surrounding part of this articular surface. The tips of these surrounding processes extend almost to join at the back of the retroarticular (Figure 6A-C, Figure 8B, Figure 10).

The retroarticular is a pyramidal and stout bone (Figure 6). This bone forms the ventroposterior end of the lower jaw because it is attached laterally between the articular and ventral processes of the anguloarticular bone. In most of the specimens studied here, the retroarticular and anguloarticular are disarticulated, suggesting that these bones showed cartilaginous sutures in life. The coronomeckelian is a small, flat, untoothed, and comma-shaped bone medially attached to the anterior process near the interior angle of the anguloarticular (Figure 6, Figure 8B, Figure 10).

The toothed surface of the dentary shows teeth similarly shaped and ordered as those described in the premaxilla (Figure 6A-C, Figure 8B, Figure 10, Figure 11). This bone also has two kinds of teeth; six or seven long bicuspid teeth, thick and stake-like based along the labial or principal row, and an indeterminate number of smaller unicuspid teeth forming a lingual or secondary tooth patch (Figure 8C, Figure 10, Figure 11).

Suspensorium. IGM 13123 shows the bones of the suspensorium series complete and articulated (Figure 8D). This comprises the palatine, quadrate, hyomandibula, symplectic, and endopterygoid. These bones are ordered, forming an U-shaped structure. The metapterygoid and ectopterygoid bones are absent. Here, the palatoquadrate arch, formed on the anterior edge and between the heads of the quadrate and palatine, is straight and strongly tilted vertically. The palatine is a triangular laminar bone, about two times higher than long, smooth, with an imbricated suture for the quadrate and endopterygoid. The palatine articular head is narrow and has a small dorsal process protruding anterolaterally (Figure 6A, Figure 8D).

The quadrate bone is a triangular bone. Its posterior edge is somewhat concave, whereas its ventral and anterior edges are relatively straight, form an obtuse angle close to 115°, and join the base of the mandibular articular head. This head is robust, slightly protuberant forward, and bicondylar, in which the medial condyle is larger than the lateral one. The incisura for the symplectic is broad and deep and separates the laminar body of this bone from its posterior process, which is markedly thicker and has a sharp tip.

The symplectic is a long triangular bone, anteriorly acute, posteriorly expanded, and dorsoposteriorly projected (Figure 6A). It is almost two times longer than the quadrate and joins at the base of the hyomandibular. The endopterygoid [also identified as mesopterygoid by Kobelkowsky (2005, fig. 2) and ectopterygoid by Smith (1980, fig. 15)] is a weak laminar and oblong bone, ventrally expanded, and dorsally tapered. The posteroventral part of the endopterygoid occupies the quadrate’s posterior notch, and its anterodorsal end is attached to the base of the rear edge of the palatine. The hyomandibular is an axe-shaped bone with a short handle, an expanded rectangular body, and two long articular facets (Figure 8D). The opercular process barely projects near the middle of the posterior edge of the hyomandibula.

Opercular bones. This bone series includes the opercle, preopercle, subopercle, and interopercle (Figure 6). The opercle is a triangular bone laminar, slightly longer than high, and superficially convex; in which the dorsal edge is slightly concave; the anterior border is straight and thick; and the posterodorsal end becomes narrow, somewhat elongated, and rounded. Anterodorsally, the opercle exhibits a short rectangular articular process (= preopercular arm) that protrudes anterodorsally and forms an obtuse angle of about 130-140° with the anterior edge of the bone. On the contrary, in the medial surface of this bone, near its anterior border and at the base of its articular facet (=opercular facet), is a shallow and semispherical concavity that occupies the center of a superficial and oblong structure that protrudes medially.

The preopercle shows the typical inverted L-shape with the horizontal and vertical limbs similarly shaped, forming an angle of about 90° plus a well-developed medial shelf, uniformly expanded, and a rounded anterior edge (Figure 6A, Figure 8D). Alongside the ventral and posterior edge, this bone displays a deep groove roofed by a thin laminar shelf, in which four or five pores of the preopercular sensory canal open, three of them in the horizontal limb and the others in the vertical one (these pores are visible under the microscope with the specimen wet with alcohol).

The subopercle is a sickle-shaped laminar bone with an anterior ascending process that is small, thorn-like, and subterminal (Figure 6, Figure 10). This bone and the posteroventral edge of the opercle are equally long. In the subopercle, the anterior border is high and convex, the dorsal and ventral edges are harmoniously curved, and the posterior end is acute. The interopercle is a long triangular bone, slightly curved dorsally, rounded posteriorly, and sharp anteriorly (Figure 6). The preopercle covers a large part of the interopercle; however, its anterior tip is so long that it almost reaches the articular head of the quadrate.

Hyoid arch and branchial apparatus. IGM 13127 shows the bones of the hyoid arch and branchial apparatus (Figure 6A, D). The ventral hypohyal is a solid pyramidal structure anteriorly pointed. Behind this, the anterior ceratohyal is an unpierced rectangular bone, lateromedially flattened, slightly constrained in its anterior half, and expanded in its anterior and posterior ends. The posterior ceratohyal is a solid triangular bone, probably equally longer than high. The anterior ceratohyal is anteriorly and posteriorly tightly attached to the respective ventral hypohyal and posterior ceratohyal. The urohyal is a long bone with a slight anterior articular head plus two triangular longitudinal wings posteriorly projected; the horizontal one forms the ventral edge of the bone, and the vertical one projects dorsally.

Although sometimes poorly preserved, in this fish, there are always five pairs of branchiostegal rays (Figure 6A, D). The shape of these laminar, long, and curved bones varies in anteroposterior order, from thread-like to saber-like structures. Among these bones, the anterior four are proximally joining the anterior ceratohyal, while the posterior one does this with the posterior ceratohyal.

Numerous elements of the branchial apparatus are obscured or poorly preserved in the fossils studied here. In IGM 00024 (Figure 6A, D), the basihyal is a long bone, trapezoidal, somewhat slender and expanded anteriorly, and has a small posterior articular head. The same specimen also shows a minute thorn-like interhyal bone; however, this does not preserve the basibranchial bones that once separated the basihyal and interhyal bones.

Other bones of the branchial apparatus, such as the hypobranchials, ceratobranchials, epibranchials, pharyngobranchials, and gill rakers, seem present in different specimens studied herein; however, these are so cracked and incomplete that their identification and description are difficult. These include at least a lower and an upper pair of expanded gracile-toothed pharyngobranchial plates and associated posterior branchial bones. In these plates, the teeth are conic, very robust, and irregularly sized, with the tip curved backward and implanted in shallow sockets (Figure 8G). Although these teeth are usually unattached and dispersed between the medial surfaces of the opercular bones, those placed in the middle are so high that they equal or exceed the thickness of such plates.

Axial skeleton. The numbers of centra and ribs vary slightly in males and females (Table 1). In males, the vertebral column consists of 34-35 total centra, including 15 abdominals and 20 caudals. On the contrary, females have 31-32 total centra, 13-14 abdominals centra, and 17-89 caudals. The rib pairs are 15 in males and 12-13 in females. All the centra are autogenous, but the last three fuse into the caudal complex (Figure 14).

All centra are hollow, deep amphycelic, and hourglass-shaped; these are constrained in the middle, equally expanded anterior and posterior, and show circular intervertebral surfaces. Although it is difficult to determine if most anterior abdominal vertebrae have unfused neural arches, all the other centra fuse with the respective hemal and neural arches. At least four abdominal centra (probably the 2 to 5) show neural crests expanded, rectangular, and laminar. The ribs are long, thin, and slightly curved, enclosing almost the entire abdominal cavity; these join the dorsal surface of the paraphyses (= transverse processes in Kobelkowsky, 2005, figure 4), which are straight, long spiny-like structures projected laterally from the dorsal part of the centra, that show a lateromedial groove in its dorsal surface. At least, the anterior half of the ribs are associated with thin epineural bones, which are about two centra long and lie horizontally (Figure 8F).

Pectoral fin and girdle. The pectoral fin is rounded and has 12 rays in males and 13-14 in females (Table 1). These rays are distally branched and segmented, uniformly thin, and extend, covering the anterior third of the abdominal region. At least four rectangular radials support this fin.

The posttemporal is a long triradial bone (Figure 6A). This bone is oblong, thin, short, and posteroventrally projected. In contrast, its anteroventral process is small and triangular, while its anterodorsal limb is a bar-like structure, uniformly wide, curved dorsoventrally, slightly flattened, and about four times longer than the anteroventral process. The supracleithrum is a flat bone, short and drop-like, that rests above the dorsoposterior end of the cleithrum. Since the highly compressed preservation of the specimens studied here, only the lateral surface of the cleithrum is identifiable; this thin bone is crescent- shaped and bears a laminar posterior extension with a slightly curved edge. Two postcleithra are present; the first is an ovoid plate in the rear corner of the cleithrum, and the other is a sinuous rod-like structure projected ventrally. The posterior wing of the cleithrum covers a large part of the scapula; however, its rear surface is exposed, showing its articulation with the pelvic radials. Otherwise, only the lateral surface of the coracoid appears as an elongated laminar and triangular structure that is posteriorly expanded and has a ventroposterior end convex, with a posterior margin vertically tilted and anteriorly limited by a narrow and deep notch (Figure 6A).

Pelvic fin and girdle. The pelvic fin is entirely opposed to the predorsal region of the trunk. It rises in the posterior half of the body, at 57.3 SL in males and 64.8% of SL in females. The posterior edge of the fin does not reach the origin of the dorsal fin. This small and rounded fin consists of six pelvic rays that are distally segmented, branched, and have bifid articular heads (Table 1, Figure 12). There are no pelvic radials.

The pelvic bone is triangular, about two times longer than wide, laterally and medially almost straight, and anteriorly acute. The dorsal surface of this bone bears a middle thickening bar or keel. The posterior edge of the pelvic bone is concave and shows small facets to join the pelvic rays. In small specimens, this bone shows a shallow posterior notch and three processes relatively small, including an inconspicuous lateral process, a small and rounded medial process, and a stout triangular ischial process (Figure 12A). On the contrary, the pelvic bone of larger fishes has a posterior notch conspicuous, a lateral process wider and rectangular, and a long thick medial process that is somewhat sinuous (Figure 12B).

Dorsal fin. The dorsal fin is rounded, long, and about equally high than long (Figure 13A). The number of rays from this fin is sexually variable; males have 15 dorsal rays, while females show only 12. The dorsal rays are uniformly thin and distally branched and segmented. Here, the first three and last rays are comparatively smaller than the others.

A series of long and straight dorsal proximal pterygiophores support the dorsal fin rays in a numerical relation 1:1. The series has no distal pterygiophores but includes small square-like medial dorsal pterygiophores in at least three anterior quarters of the dorsal fin. Along the series, the size of the proximal dorsal pterygiophores is almost the same and are so long that they penetrate the interneural spaces present immediately below.

Anal fin. The anal fin is high, long, and rounded; in general, this is a little smaller and located slightly behind the dorsal fin (Figure 13B, Table 1). This fin comprises around 16 rays (between 15 and 18) in both sexes; the first ray is rudimentary. In males, the subsequent six rays form the andropodium; these rays are segmented, unbranched, shorter than the posteriors, and crowded together. Due to the difference in size, the andropodial rays are separated from the subsequent by a small notch. Posterior anal rays are distally segmented, branched, and at least 20 % longer than the last andropoidal rays. The rear three anal rays decrease in length progressively.

A series of proximal pterygiophores internally support the anal fin. These rod-like bones are straight, and so elongated that they penetrate the interhemal spaces. In extreme cases, these proximal pterygiophores cover three-quarters of the distance between the vertebral column and the base of the fin (Figure 13B). The numerical relation between anal rays and proximal pterygiophores is 1:1, except for the first pterygiophore that joins the first two anal rays. There are no distal pterygiophores. The anterior medial pterygiophores are absent or probably fused with the articular head of the anterior seven proximal pterygiophores, which are close-set, mainly the first five; therefore, these proximal pterygiophores are the only ones supporting the andropodial rays. Beyond, a robust rectangular medial pterygiophore is present between the posterior proximal pterygiophores.

Caudal fin. The caudal skeleton involves the neural and hemal spines of the preural 1-3 plus those bones associated with the ural centra (Figure 14). These spines become thicker, broader, and slightly less tilted than those of previous centra. The parhypural and the hemal spines of preural centra 2 and 3 are so broad that they are in contact. The parhypural has a wide proximal tip, probably fused with preural 1. A single wide epural fills the space between the most posterior neural spine and the ural plate. As in other cyprinodontiforms, the end of the vertebral column, the caudal complex involves the fusion of the preural 1, urals 1, and an undetermined number of hypurals (see Thieme et al., 2021). The hypurals form a fan structure with a long conspicuous interhypural foramen longitudinally bordered by two shallow ridges. Near its base, this caudal complex shows three small processes; the urostyle is a small and rectangular anterordorsal process that is projected upward and seems to embrace the anterior tip of the epural; in the base of the hypural plate, there is a small spine-shaped process and a keel-shaped process laterally expanded in dorsal and ventral position, respectively.

The caudal fin is rounded and posteriorly expanded. Its dorsal and ventral lobes form a harmonious convex profile, while the ventral and dorsal edges of the fin are straight. This fin is relatively short, and its length is about 1.2 times the postanal length of the trunk. Regarding those caudal rays anteriorly associated with the caudal complex, the caudal formula is vi+ I+9—8+I+v. In both lobes, the procurrent rays become longer and thicker in anterior to posterior order.

Scales. The scales cover the whole body, head, jaws, and caudal skeleton 8 (Figure 3, Figure 4, Figure Figure 5, Figure 8F, Figure 13, Figure 14). These are cycloid scales, rounded to slightly ovoid, in which the center half is smooth. The surrounding scale surface has 4-9 concentric circuli that are sinuous, unbranched, and evenly separated. Additionally, most scales covering the anterior third of the trunk have 3-12 straight, horizontal, and parallel radii. In small specimens, only a few scales of the middle part of the trunk show radii, while in larger fishes, the radii are present in more scales. Regardless of the size of the specimens, the scales on the head and jaw have no radii. On the trunk, scales are evenly sized; however, those on the occiput and the head become smaller. Middle longitudinal scale lines on the skull extend symmetrically on each side up to the frontal-mesethmoid contact. Nine to 10 scale rows probably cover the height of the trunk, and about 32 rows extend above the vertebral column between the head and the anterior tips of the caudal fin rays.

Coloration pattern. UV light allows us to recognize some details of the color pattern of Paleocharacodon guzmanae gen. and sp. nov., which are invisible under white light. IGM 13117 shows 14 wide dark color spots covering the posterior surface of the abdominal cavity, four behind the pectoral girdle and over the first vertebrae, and at least another five or six (barely observable in the specimen) forming a longitudinal row above the vertebral column, between the pectoral girdle to the middle part of the anal fin. Additionally, a large dark color spot is present along the basal half of the anal fin (Figure 3).

Such spots of color are not present in all the fishes of Sanctórum, probably because the multiple taphonomic factors that controlled and allowed their conservation did not affect all individuals uniformly. Otherwise, the rare preservation of these color spots could respond to the fact that, when collected, many of these fish open in half and therefore do not show their exterior surface details.

Reproduction. Skeletal remains attributable to unborn small fishes preserved in the abdominal cavity of some of the females, as IGM 13117 and IGM 13125 (Figure 5B), evidence the viviparity of Paleocharacodon guzmanae gen. and sp. nov. Although it is challenging to identify complete individuals in these remains, here, we rule out the possibility that these remains represent stomach contents because these do not show any signs of decay by digestion.

For almost 150 years, at the same time as the knowledge of the taxonomic diversity of fishes now included in the family Goodeidae increased, different authors discussed their possible interrelationships under both pre and post-Hennigan considerations (Figure 15). Unfortunately, in most of these efforts, the evidence considered is non-osteological, with unverifiable attributes in fossil specimens. These first studies only considered general phenotypic body traits and soft structures, particularly those linked to their reproductive strategies (Hubbs and Turner, 1939; Gosline, 1949; Fitzsimons, 1981). Subsequently, the phylogenetic studies carried out in the last 25 years involved molecular data of alloenzymes and different genetic materials, show somewhat contradictory results (Grudzien et al., 1992; Webb, 1998; Doadrio and Domínguez, 2004; Domínguez-Domínguez, 2010; Parker, 2017; Parker et al., 2019). Today, determining the taxonomic identity and the phylogenetic relationships of fossil goodeids, such as Paleocharacodon guzmanae gen. and sp. nov. and Tapatia occidentalis, are complex tasks because the osteological features of these extinct fishes have been unnoticed in such studies. Therefore, the present authors have begun an osteological descriptive and comparative analysis of members of the family Goodeidae, which now gathers about 21 genera and 50 species (Table 3), an effort that will still take us several years. Despite this restrictive scenario, those osteological features of fossils and extant goodeids previously discussed by different authors (e.g., Miller and Fitzsimons, 1971; Smith, 1980; Parenti, 1981; Webb, 1998), together with the results of our observations on recent specimens, are used here to recognize the taxonomical peculiarity and affinities of P. guzmanae.

Webb (1998) performed a phylogenetic study of Goodeidae, combining molecular and morphological data. He identified five Goodeinae tribes, including Characodontini (Characodon), Goodiini (Goodea and Ataenobius), Ilyodontini (Ilyodon, Allodontichthys, and Xenotaenia), Girardichthyini (Girardinichthys, Allotoca, and Hubbsina), and Chapalichthyini (Chapalichthys, Allophorus, Ameca, Xenotoca, Xenoophorus, and Xanotaenia) (Figure 15); additionally, in his hypotheses, Skiffia and Zoogoneticus are like jumping-joker cards because their relationships are problematic. Currently, such tribe names are used even though, in the most recent hypotheses (Figure 15), the groups obtained are not always those of Webb’s. In this manuscript, we consider these tribe names.

Paleocharacodon guzmanae, a New Goodeidae

Smith (1980) divided Goodeidae into two large groups. His Characodon-group shares two features, the anguloarticular bone (=articular-angular) has a dorsal process projected almost vertically, forming a nearly right angle with the anterior process, and the articular head of the quadrate is comparatively short and hardly protrudes from the anterior edge of the palatopterygoid complex. On the contrary, in his Goodea-group, the anguloarticular has a dorsal process strongly projected backward beyond the articular process and forming an obtuse angle with the anterior process; additionally, here, the articular head of the quadrate is comparatively longer and projects in advance of the anterior edge of the palatopterygoid complex (Smith, 1980, figures 16, 17). Although Smith (1980) considered Ameca, Hubbsina, and Tapatia occidentalis as goodeids of uncertain position, the subsequent reviews of these taxa reveal that their anguloarticulars have a vertical dorsal process (Guzmán 2010, figure 4b; Webb, 1998), suggesting that these may form part of his Characodon-group.

In this context, it is impossible to include Paleocharacodon guzmanae gen. and sp. nov. in any of the goodeid groups proposed by Smith (1980). This Mexican fossil fish shows the condition of the anguloarticular described in the Characodon-group, as well as the quadrate having an articular head comparatively long and protruding forward as in the Goodea-group (Figure 6, Figure 8D). Additionally, Tapatia occidentalis and P. guzmanae differ in the shape of the anguloarticular and jaw teeth. In T. occidentalis, the length of the anguloarticular anterior process is at least 2.5 times the height of its dorsal process. The teeth in the frontal rows of jaws show a bicuspid or bifid shape, end in two square lobes loosely separated, and are distally truncated or straight (Guzmán, 2010, figures 4b, 5 c”). On the contrary, in P. guzmanae, the proportions of the anguloarticular are less contrasting. That length is just about 1.3 times such height, and the teeth of principal rows have bicuspid and sharp ends (Figure 6, Figure 10, Figure 11).

Also, Paleocharacodon guzmanae differs from Hubbsina and Ameca in the size and position of the dorsal fin. In P. guzmanae, the dorsal fin is short, has 12-15 rays, and is entirely opposed to the anal fin (Table 1, Figure 13). Although the dorsal fin in Ameca is short and has only 13-14 rays, in Hubssina, this fin is peculiarly long and consists of 29-37 rays; in both cases, the dorsal fin is placed more to the front and opposes the anal fin only in part (De Buen, 1940; Miller and Fitzsimons, 1971; Domínguez-Domínguez et al., 2005, p. 540, 552). As a result, P. guzmanae is considered a new genus and species.

Unfortunately, after the efforts of Parenti (1981) and Webb (1998), who included some osteological features to define the naturalness of the family Goodeidae and recognize its interrelations under the cladistic scope (Figure 15), this type of data ceased to be considered in phylogenetic assays. Therefore, under these conditions, it is necessary to analyze, recognize and assess the possible osteological differences between these fishes, a task already in progress that will take a few more years to be helpful. In this paper, we explore the affinities of Paleocharacodon guzmanae gen. and sp. nov. within Goodeidae, analyzing the distribution of its osteological features along the branches of those hypotheses proposed by these authors. Table 4 summarizes the comparative analysis of P. guzmanae and other extant and extinct goodeid taxa.

In the restructuring of Goodeidae suggested by Parenti (1981, p. 515-516) to include the subfamilies Goodeinae and Empetrichtyinae, she noted that these fishes share four diagnostic features (1-4 below and in Figure 15). Later, Webb (1998) discovered other distinctive features of the family (5-7 in this paragraph and Figure 15); however, among these features, only two are synapomorphies (3 and 5). In this context, Paleocharacodon guzmanae gen. and sp. nov. is an unquestionable member of Goodeidae because it shows six of these diagnostic features (Figure 15):

1) In the anal fin, the most anterior 2 to 7 medial pterygiophores (= middle radials) are absent as autogenous bones because these are fused with the respective proximal pterygiophores (= proximal radials of Parenti, 1981, figure 83, node A) (Figure 13).

2) The dorsal process of the maxilla is strongly reduced (Parenti, 1981, figure 83, node A) (Figure 6, Figure 8D).

3) The distal arm of the premaxilla is straight (Smith, 1980; Parenti, 1981, figures 40C, 83 node A) (Figure 6A-B; Figure 8D); according to Webb (1998, ch. 649), this is a synapomorphy.

4) The anguloarticular (=articular in Parenti, 1981, p. 406, figures 33B, C, D, and node A in figure 83) is significantly reduced, and its medial extension does not carry the mandibular sensory canal.

5) In lateral view, the lacrimal bone is somewhat rectangular and at least twice as higher as long; according to Webb (1998, figures III.22B, ch. 658) is a synapomorphy (Figure 5).

6) The ascending process of the premaxilla is small or reduced (Parenti, 1981, figure 39C; Webb, 1998, ch. 650) (Figure 6). In goodeids, in dorsal view, the pterotic (=autopterotic) bones show a narrow autopterotic fossa

7) in Figure 15), in which the otic sensory canal runs (Uyeno and Miller, 1962; Parenti, 1981; Webb, 1998, figures III.12B, ch. 641); unfortunately, any of the specimens of P. guzmanae herein studied show that fossa.

Paleocharacodon guzmanae, a New Goodeinae

Paleocharacodon guzmanae gen. and sp. nov. is also an undeniable member of Goodeinae because it was a viviparous species and shows both the homoplasy and synapomorphy that support this subfamily (8 and 9 in Figure 15, Table 4). Following the numbering of the anterior paragraph, these features include:

8) The anterior anal fin ray is rudimentary (Parenti, 1981, figure 83, node B) (Figure 13).

9) The andropodium or pseudophallus is present and formed by the unbranched anterior anal-fin rays that crowd together (Figure 13), separated by a notch from the rest of the fin, and reduced between 50-80% concerning the subsequent posterior rays; Webb (1998, p. 75, ch. 684 in part) discovered this remarkable osteological synapomorphy. Additionally, Webb (1998, p. 61 and 92, ch. 637) suggested that the appearance of a shallow neurocranium (in which the height is equal to or less than half of its width) also supports the Goodeinae monophyly; however, this condition may represent a plesiomorphy because it is present in Empetrichthyinae and other Cyprinodontiformes, too.

Eight osteological features support the naturalness of Empetrichthyinae. These include four synapomorphies (11-18 in Figure 15, Table 4), previously noticed by Parenti (1981) and Webb (1998). Paleocharacodon guzmanae gen. and sp. nov. differ from Empetrichthyinae because it does not have any of its diagnostic features. Following the numbering of the anterior paragraphs, these features include:

10) The lack of the pelvic fin and girdle (Parenti,1981, node C in figure 83; Webb, 1998, ch. 673). On the contrary, the pelvic fin and girdle are well-developed in P. guzmanae (Figure 12).

11) The epibranchial 1 is nearly Y-shaped, notched at its base, and has a lateral process (Parenti, 1981, node C in figure 83 and figure 47B; Webb, 1998, ch. 668). Unfortunately, the epibranchials are unknown in P. guzmanae, but among goodeines this bone is rod-shaped.

12) The surface of neurocranial, suspensorium, and hypural bones are rugose and irregular due to pits and ridges (Webb, 1998, ch. 643). On the contrary, these bones are superficially smooth in P. guzmanae (Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8D, Figure 14).

13) The anterior margin of the vomer is abruptly concave medially (Uyeno and Miller, 1962; Webb, 1998, figure III.9C, ch. 629). Sadly, the vomer is unknown in P. guzmanae.

14 and 15). The frontal has a supraorbital canal partially ossified and does not show the break 4a-4b (Gosline, 1949; Fitzsimons, 1981; Webb, 1998, chs. 632 and 634) (Figure 15). On the contrary, as in other goodeines, in P. guzmanae, the frontal bone entirely encloses the supraorbital canal that shows the break 4a-4b (Figure 7).

16) The dorsal and ventral pharyngobranchials are relatively robust; their bases are deep, ossified, and higher than their teeth (Webb, 1998, ch. 667). Although in P. guzmanae, the toothed pharyngobranchial plates are not well-exposed, in this species, such plates are rather gracile and bear large teeth of varying size, usually rest unattached and scattered; here, the most prominent pharyngobranchial teeth are higher than the pharyngobranchial plates.

17) Third postcleithrum with a posteriorly directed laminar plate at its mid-length (Webb, 1998, ch. 672). P. guzmanae has only two postcleithra.

Palaocharacodon guzmanae and Other Goodeines

Paleocharacodon guzmanae gen. and sp. nov., Goodiini, Characodon, Xenotaenia, and some species of Allotoca share a primitive feature; the dorsal fin is far in the back of the body (the predorsal length is equal or greater than 67% of SL). Hence, P. guzmanae differs from Ilyodontini, Girardichthyini (less some species of Allotoca), Chapalichthyini (including Zoogoneticus and less Xenotaenia), and Skiffia that have the dorsal fin located not so far back (the predorsal length is equal or less than 67% of SL)

18) (in Figure 15, Table 4) (Miller, 1948; Webb, 1998, p. 77, ch. 689).

According to Webb (1998, p. 61, ch. 637), all goodeines except Goodiini, Ilyodontini, and Alloophorus show a neurocranium primitively low; in the posterior view, its height/width ratio is 0.45 to 0.52. On the contrary, in other goodeines, the neurocranium shows a higher derived condition, and the range of such proportion is 0.58 to 0.66

19) (in Figure 15, Table 4). This character had a regressive change to the shallow state in Ilyodontini and Alloophorus (19* in Figure 15). Unfortunately, the neurocranial proportions of Paleocharacodon guzmanae gen. and sp. nov. and Tapatia occidentalis are unknown.

Into Goodeidae, only Goodiini and Empetrichthyinae possess rostral cartilages (Webb, 1998, p. 63, ch. 644). Other goodeids have no rostral cartilage

(20 in Figure 15, Table 4). The presence or absence of this cartilage is unknown in Paleocharacodon guzmanae gen. and sp. nov. and Tapatia occidentalis.

According to Webb (1998), Goodea and Ataenobius form the tribe Goodiini. In one of his hypotheses, this tribe is the sister group of other goodeines, while in the other, this constitutes a natural group with Skiffia. Two unambiguous characters, a synapomorphy, and a homoplasy, support this tribe in Webb’s hypotheses. The first is the presence of lateral wings in the anterior end of the parasphenoid

21) (in Figure 15 and Table 4; Webb, 1998, p. 61, ch. 638). The homoplasy is the presence of a pelvic fin relatively short because its posterior edge does not reach the dorsal fin origin

22) (in Figure 15 and Table 4; Webb, 1998, p. 72, ch. 675). A short pelvic fin is also present in Characodon and Allotoca (see Domínguez- Domínguez et al., 2005, p. 545, 547). In other goodeids, the parasphenoid has no wings because its anterior lateral edges are parallel, and the pelvic fin is long and goes beyond the dorsal fin origin. Although the pelvic fin of Paleocharacodon guzmanae gen. and sp. nov. is short, it is recognized as non-Goodiini fish because its parasphenoid is not winged.

In Webb’s (1998) hypotheses, the long and well-developed posterior process in the epioccipital bone represents a derived condition of Goodiini and Skiffia

23) (in Figure 15 and Table 4; Webb, 1998, p. 62, ch. 640). These taxa, Ilyodontiini (except Allodontichthys polylepis, A. tamazulae, and A, zonistius), Ameca, and Xenoophorus have 20 to 54 gill rackers on the first branchial arch

24) (in Figure 15 and Table 4); Webb, 1998, p. 70, ch. 665). In other goodeids, the epioccipital process is tiny, and the first branchial arch has only 9 to 19 gill rackers. Unfortunately, Paleocharacodon guzmanae gen. and sp. nov. and Tapatia occidentalis do not expose either of these features.

25 and 26) (in Figure 15 and Table 4; Webb, 1998, chs. 645-647, respectively). The crowns of primary jaw teeth are distally flattened, bicuspid, and straight or broadly blunted, and its bases are loosely attached to the jaws by cartilage in Goodiini, Skiffia, Ilyodon, and Xenoophorus also shows (e.g. Hubbs and Turner, 1939). On the contrary, other goodeids and Paleocharacodon guzmanae gen. and sp. nov. (Figures 8, 10, 11) have primary jaw teeth bicuspid, acute, which bases are co-ossified with the bone of jaws. According to Webb (1998), Allodontichthys shows tricuspid or shouldered teeth and large specimens of Skiffia multipunctata also have strong tooth attachments.

Additionally, Goodiini, Skiffia, and Ilyodon share a derived condition of the anguloarticular bone; its dorsal process projects backward, forming an angle of about 180°

27) (in Figure 15; Smith, 1980, figure 17B; Guzmán, 2010, figure 9; Webb, 1998, p. 66, ch. 654). On the contrary, Paleocharacodon guzmanae gen. and sp. nov. and other goodeids show the alternative primitive condition of this bone; its dorsal process is projected dorsally and forms an angle of about 90° with its anterior process (Figure 6, Figure 8B, Figure 10).

Among goodeids the ventroposterior coracoid region is variable (Webb, 1998, p. 71-72, ch. 671). This region shows a straight angle in Empetrichthyinae, most Goodeiinae, and probably in Tapatia occidentalis; on the contrary, in Skiffia, this is broadly convex

28) (in Figure 15 and Table 4), and in Ilyodon varies between straight and convex. Only in Ameca, Xenotoca variata, and now Paleocharacodon guzmanae gen. and sp. nov, this region is convex, has a posterior margin vertically tilted, and is anteriorly limited by a narrow and deep notch (Figure 6; Webb, 1998, figure III.27). In this case, the condition shared by Ameca, X. variata, and P. guzmanae seem an evolutive convergence.

Furthermore, Webb (1998, p. 67-68, ch. 657) noted that in Goodiini and Skiffia, the palatoquadrate arch (between the articular heads of the palatine and quadrate bones is about vertically inclined

29) (in Figure 15 and Table 4). On the contrary, this arch is bent forward in other goodeids, including Paleocharacodon guzmanae gen. and sp. nov. (Figure 8D).

Likewise, Goodiini, Skiffia, Ilyodon, and Ameca share a homoplasic and derived feature, the retroarticular bone forms the lingual part of the articular facet for the quadrate

30) (in Figure 15 and Table 4; Webb, 1998, p. 67, ch. 655). On the contrary, this bone does not form that facet in other goodeids. In Paleocharacodon guzmanae gen. and sp. nov., that facet has a donut-like configuration in which the retroarticular forms its central region and the anguloarticular has two curved processes forming its surrounding part (Figure 6, Figure 8B). Although this donut-like configuration of the articular facet for the quadrate (added in this work as

character 31 (in Figure 15 and Table 4) was observed only in specimens of Characodon, additional observations are required to clarify its possible occurrence in other goodeids.

Based on Webb’s hypotheses, among goodeids, there is a primitive anterolateral projection in the palatine head of Empetrichthyinae, Goodiini, Ilyiodontini, and most Chapalichthyini (except for Alloophorus, Zoogoneticus, and Skiffia francesae). A convergent derived state of these characters, the lack of such projection in the palatine occurs in Characodontini, Girardinichthyini, Alloophorus, Zoogoneticus, and S. francesae

32) (in Figure 15 and Table 4, Webb, 1998, p. 67, ch. 656). Herein, Paleocharacodon guzmanae gen. and sp. nov. and is excluded from Chacarondontini and Girardinichthyini because it shows the primitive anterolateral projection of the palatine.

Herein, we identify that Paleocharacodon guzmanae gen. sp. nov. and Characodon spp. Differ from each other in at least three different features. In the last, the openings of the supraorbital canal show a formula—1-2a, 2b-7— as in some Allodontichthys species (Fitzsimons, 1981, table 1); its posttemporal is unforked because the anteroventral process is absent as in Empetrichthyinae, Girardichthyini, and Zoogoneticus (33 in Figure 15 and Table 4; Webb, 1998, p. 71, ch. 669); and the parasphenoid bone shows outstanding dorsal wings extended in its orbital part. On the contrary, in the fossil species, the openings of the supraorbital canal show a formula never recorded before among goodeids—1-2a, 2b-3a, 3b-4a, 4b-5a, 5b-7—(Figure 7); its parasphenoid bone shows tiny ventral and lateral wings in its orbital part, (Figure 6); and its posttemporal bone shows a small anteroventral process that may be an intermediate condition observed in other goodeids (Figure 6).

Unfortunately, in his hypotheses, Webb (1998), most no-Goodiini, and no-Characodontini groups do not have osteological supporting features. Therefore, it is not easy to compare the anatomy of such groups with those features observed here in Paleocharacodon guzmanae gen. sp. nov. In the present context, after mapping the osteological features of P. guzmanae into Webb’s hypotheses, it is possible to point out that this fossil is part of the family Goodeidae and the subfamily Goodeinae (it shows the characters 1-6, 8-9 in Figure 15). In addition, the mixture of characters of this fossil goodeid does not allow us to recognize it as part of any of the tribes of Goodeinae. Besides, this fossil goodeid does not share features with the tribes and shows different characters to those that support such tribes or groups of tribes (numbers in italics in Figure 15). On the other hand, this fossil and the tribe Characodontini shared more features (numbers in bold in Figure 15), but it shows significative differences with its single member, Characodon. Therefore, the species described here was included in its genus, Paleocharacodon, to highlight its similarity with Characodon, including a feature observed for the first time, the donut-like articular facet for the quadrate.

Phylogenetic and Biogeographic Implications

Despite numerous recently published hypotheses (Doadrio and Domínguez, 2004; Webb et al., 2004; Domínguez-Domínguez et al., 2010; Foster and Piller, 2018), the phylogenetic and biogeographic relationships of Goodeidae are still unclear (Figure 15). This situation probably results from the lack of suitable fossil evidence that allows us to recognize the history of the morphological changes of Goodeidae, as well as the geological-environmental conditions in which they occurred. The discovery of Paleocharacodon guzmanae gen. and sp. nov. not only complements our knowledge about the diversity of the family, but it also reveals itself as an element to consider in future biogeography studies.

The accurate osteological description of living goodeids is a pending task that avoids the comparison of its extinct and recent species. Despite this, the analysis of Paleocharacodon guzmanae gen. and sp. nov. and some data published of other goodeids reveals that this new fish does not belong to any goodeine tribes. The putative primitive features of P. guzmanae suggest that it may represent a primitive goodeinae. Such observation is congruent since P. guzmanae is a Pliocene species of at least 4 Mya. In any case, assessing the relationships of fossil goodeids, such as P. guzmanae, Goodea-like from Sanctórum, and Tapatia occidentalis requires a comprehensive phylogenetic study involving osteological data of recent and fossil goodeids.

In the biogeographic hypotheses of Goodeidae so far proposed, Goodeinae arose in the northwestern region of Mexico and had different episodes of diversification in the central part of this country. Such diversification seems more successful in rivers and lakes of the western and southern of the country, which today concentrate most of the known species. Later, some of its genera experienced exchanges between these regions (Gesundheit and Macías, 2005; Domínguez-Domínguez et al., 2006, 2010; Pérez‐Rodríguez et al., 2015, Foster and Piller, 2018; among others). The finding of Paleocharacodon guzmanae gen. and sp. nov. and his contemporary Goodea-like in Sanctórum is significant. The Pliocene strata of the extinct Paleolake Amajac are within the domains of the Pánuco-Salado Basin on the eastern side of Mexico, where there are only six recent species (Table 3, Figure 16). The contrasting diversity of goodeids between the western-southern and eastern regions of Mexico seems linked to the geological-environmental history of the country. On the one hand, during the Neogene, the development of the TMVB strongly and continuously affected its western and southern regions, while the eastern area occupied by the Pánuco-Salado basin was relatively more stable. For now, the uncertain relationships of P. guzmanae within the goodeids hinder the recognition of whether this supports or rejects the biogeographic hypotheses already proposed; however, our study suggests that this extinct species of the eastern slope of Mexico is not directly related to any species from the Pánuco-Salado Basin.

Additionally, divergence dates in the Goodeidae evolution are available in the most recent phylogenetic studies (Figure 15); Foster and Piller, 2018; however, the discovery of Paleocharacodon guzmanae gen and sp. nov. suggests that a different goodeinae lineage without living representatives must have existed. According to these data, the family Goodeidae and the subfamilies Goodeinae and Empetrichthyinae rose during the early Miocene, before 15 Mya; in the later 5 My and during the middle Miocene, between 15 and 10 Mya, the goodeines tribes separated; and finally, since then the diversification of these fishes led to the establishment of all genera and species hitherto known. As demonstrated in the previous section, the available evidence from Tapatia occidentalis and P. guzmanae indicates that these Miocene and Pliocene fossil species are part of Goodeinae. However, their inclusion at the tribe level is impossible and may represent unknown members of other lineages.

The situations described in the two previous paragraphs suggest that the biogeographic history of goodeids is more complex than those described so far. Such a process may include at least two alternative early scenarios: A) Early goodeids were widely distributed in Mexico and B) The eastern slope of Mexico received an ancient group of goodeids from the northwest region, subsequently displaced by more recent species.

The geographic distributions of Goodeidae and Profundulidae are disjoint, adjacent, and separated by the Sierra Madre del Sur. The first family inhabits the north, between the southwestern USA and the Mesa Central of Mexico, plus its neighboring regions. At the same time, Profundulidae is found further south, from the Pacific slope of the Sierra Madre del Sur and the Mixtec Basin to Guatemala, El Salvador, and Honduras (Morcillo Alonso, 2004, figure 1). Such distributional patterns respond to the development of TMVB, which began 10-20 million years ago. In this scenario, fossils of Paleocharacodon guzmanae gen. and sp. nov. are geographically nearer to the current distribution of Profundulidae and temporally closer to the origin of TMVB; however, its importance in the effort to understand the separation of these two families is minimal because Profundulidae has no fossil record.

The review of the Pliocene fish from the Paleolake Amajac deposits in Sanctórum, Hidalgo, Mexico, reveals that these represent two species of the family Goodeidae and subfamily Goodeinae. Here, one is described and named Paleocharacodon gu zmanae gen. and sp. nov.; the other, still poorly known, resembles Goodea (Becerra Martínez, 2003). The principal jaw teeth of P. guzmanae, with bicuspid and symmetrical acute-ends, noticeably differ from those of other Mexican goodeid fossils, Tapatia occidentalis and the Goodea-like of Sanctórum, in which bicuspid teeth have wide spatula-ends. A unique combination of non-exclusive and exclusive features shared with other goodeids supports the singularity of P. guzmanae. These features include the unpaired fins opposed and located far back of the body, behind the 69% of SL; the rudimentary anterior anal ray; the andropodium of males; the strong jaw teeth with distal acute and bicuspid ends; and the donut-like articular facet for the quadrate. The exclusive features of the species include the small anteroventral process of posttemporal and the formula 1-2a, 2b-3a, 3b-4a, 4b-5a, 5b-7 of the supraorbital canal openings.

As its name implies, Paleocharacodon gen. nov. shares some osteological similarities with Characodon; however, the mapping of the osteological features of this fish into the different branches of the phylogenetic hypotheses published by Webb (1998) allows us to recognize that this does not belong to any tribe of the subfamily Goodeinae. Developing a phylogenetic study of Goodeidae based on osteological data, which enables the inclusion of fossil species such as P. guzmanae or Tapatia occidentalis, still requires the accurate characterization of most of the living species of this family. Meanwhile, the inclusion of P. guzmanae in any tribe is unfounded.

The discovery of Paleocharacodon guzmanae gen. nov. in a restricted area within the Great Pánuco-Salado Basin is significant because it will provide new data for future phylogenetic and biogeographic investigations. On the one hand, this new species shares some osteological characteristics (mainly primitive) previously observed in other specimens; however, at the same time, it shows osteological novelties that may represent the key to improving our understanding of the evolution of goodeids. The recovery of this and other fossils in different Miocene-Pleistocene Mexican sites is a tempting invitation to review the skeletal anatomy of the extant and extinct goodeids and seek new evidence of their phylogenetic biogeographic interrelationships. On the other hand, the finding of P. guzmanae and Goodea-like of Sanctórum forces us to reconsider the phylogenetic and biogeographic hypotheses already published. These Mexican fossils encourage us to visualize new possible scenarios where the distribution of extinct goodeids may indicate that the origin or, at least some episodes of the early diversification of this clade, have occurred on the eastern slope of central Mexico, closer to the south of the country, where the sister group of Goodeidae, the family Profundulidae inhabits.

We are deeply indebted to Mrs. E. Liberto Álvarez and her family, inhabitants of Sanctórum and owners of the land of the Sanctórum paleontological site. The UNAM entirely funded this work through the postdoctoral scholarship of DGAPA assigned to CCV and the subventions DGAPA-PAPIIT IN115223 and IN209017 assigned to JAO and KMC. We thank Mr. J.M. Contreras for his work in the obtention of part of the photographs illustrated in this work, Biol. S. Guzmán Gómez of LaNaBio-UNAM, for her technical assistance in photography through the multifocal microscope; Dr. A.M.Reyes Salas and Chem. B.S. Angeles García of the LANGEM-UNAM and Igl-UNAM for their help using and obtention photographs in the SEM; and M. in Sc. D. Arteaga Martínez of LUMIR, Centro de Geociencias-UNAM Juriquilla, for the microtomography images included in this study. We thank G. Arratia and H.P. Shultz from the University of Kansas; Mr. G. Alvarez Reyes and C. Nuñez Alfaro, technicians of the Laboratorio de Paleontología de Vertebrados at the IGl-UNAM; as well as volunteers, undergraduate, and graduate students of both the Facultad de Ciencias and the Posgrado en Ciencias Biológicas of the UNAM, including A. Guadarrama Pérez, B. Carranza Becerra, D.P. Heredia Jiménez, E. Sánchez Fernández, E. Mendoza-Roynosa, J.J. Avedaño Pazos, M. del Pilar Melgarejo Damián. O. Hilario Bautista, P. Moctezuma Ducloud, S. Pacheco Ordaz, and T. Mejía Farfán for their invaluable help during the fieldwork in Sanctórum. Finally, we greatly appreciate the annotations of two anonymous reviewers whose reviews and comments improved this manuscript.

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The Fantastic Four are an iconic foursome that has been an important Marvel Comics property. The original Fantastic Four series helped bolster Marvel from a relatively small publisher to the behemoth it is today. The Fantastic Four is responsible for a lot of firsts for the company, including being the first Marvel superhero team.

With adaptations into films, video games, and TV series, the Fantastic Four continues to be an important part of Marvel history. Given the importance of The Fantastic Four, the comic’s big, watershed moments span decades and creative teams. As a result, the book and team originate some integral moments in Marvel lore.

12 Fantastic Four’s First Appearance

1961’s The Fantastic Four #1 by Stan Lee and Jack Kirby is the comic that started it all, introducing audiences to the Fantastic Four team. Ben Grimm, Johnny Storm, Sue Storm, and Reed Richards are turned into the Thing, Human Torch, Invisible Girl (later Invisible Woman), and Mr. Fantastic after cosmic radiation exposure during a space mission. From the beginning, the Fantastic Four were not like any other superheroes: they do not hide their identities and enjoy both the perks of fame and the dangers of being known. The first superhero team created by Kirby and Lee, this book set in motion an iconic artistic partnership that would see more joint creations for years to come.

11 Skrulls Are Introduced To Marvel Lore

An integral part of Marvel storytelling, the Skrulls were first introduced in Fantastic Four #2 by Lee and Kirby. In this issue, the Skrulls shapeshift into the Fantastic Four and commit a number of foul deeds, hellbent on destroying the heroes’ reputation to make way for their invasion. The real team saves the day with some good old-fashioned trickery that thwarts the Skrulls and redeems their reputation. The Skrulls are now woven through the entirety of the Marvel Universe. Moreover, the Skrulls have had their own essential storylines, like Secret Invasion and Meet the Skrulls. The fictional alien race has also made an impact on the MCU, playing major parts Captain Marvel and Secret Invasion.

10 The Team Take On The Hulk

In Fantastic Four #25 and #26 by Lee and Kirby, the Fantastic Four assist the Avengers in stopping the Hulk as he rampages through New York. This is the first time the Fantastic Four and the Avengers work together, and they would go on to team-up many times throughout the years. This event also catalyzes the beginning of an enduring rivalry between Hulk and Thing. One would assume that, given how much the two characters have in common, they’d be fast friends. But given that their first exposure to each other includes pounding each other to a pulp, it’s easy to see why a rivalry was established. The Hulk ultimately wins this battle, but they clash frequently down the road.

9 Inhumans Introduced To Marvel Lore

The Inhumans debuted in a five-issue storyline that began in Fantastic Four #44 by Lee and Kirby. Through Medusa, the Fantastic Four meets the Royal Family of the genetically-engineered Inhumans. Johnny falls in love with Medusa’s sister Crystal, but the pair have to separate after the Inhuman’s home is torn apart, and Johnny and Crystal go their separate ways. Many seeds of future events were planted in this first meeting, and it leads to such events as the creation of the Atmo-Gun. Since their debut, the Inhumans have made their mark in their own storylines in both comics and movies alike.

8 The Team Turn Back Galactus And Redeem The Silver Surfer

The Fantastic Four’s villains are considered more cosmic than other Marvel antagonists. The important Galactus-Silver Surfer storyline — also known as the Galactus Trilogy — began with Fantastic Four #48 by Lee and Kirby. The story introduces Galactus as an extremely powerful being who consumes planets without a care. He does so only after sending his herald, the Silver Surfer, to scout out the new worlds. This backfires on Galactus when the Silver Surfer, with the Fantastic Four’s help, decides Earth is worth protecting and turns his back on his master. This storyline introduced two compelling characters who would go on to have major roles in Marvel’s larger story, with the Silver Surfer even receiving his own comic series.

7 Sue Storm And Reed Richards Have Children

The birth of Reed and Sue’s children, Franklin and Valeria, is a major milestone for the team. Franklin’s birth occurred in Fantastic Four Annual #6 by Lee and Kirby, but he did not receive his name until Fantastic Four #94 a few years later. Born a mutant, Franklin showed powers as a toddler, cementing a new character that made the team even more powerful than before. The addition of Franklin and Valeria adds to the unique quality of the Fantastic Four as a biological family. Not many superhero teams can say they’re related, but sets the Fantastic Four apart from other heroes.

6 Doctor Doom Becomes Valeria’s Godfather

The rivalry between Mr. Fantastic and Doctor Doom has shaped Marvel’s history. The twist of all twists occurred when Reed’s detested opponent became his daughter’s godfather, forever cemented as a bizarre member of the family in Fantastic Four #54 by Carlos Pacheco, Rafael Marin, Karl Kesel, Mark Bagley, Scott Koblish, Al Vey, Liquid!, Richard Starkings, and Albert Deschesne. After a series of mishaps, Valeria was delivered by Doctor Doom using both magic and medicine. Sue and Reed were so thankful, they allowed Doom to name the child and be her godfather. It would turn out to be a mistake: Doom put an enchantment on newborn Valeria that makes her his familiar, but hindsight is 20/20.

5 Council of the Reeds Takes the Stage

The Council of Reeds was introduced in Fantastic Four #570 by Jonathan Hickman, Dale Eaglesham, Paul Mounts, and Rus Wooton, which sees Earth-616 Reed use the Bridge to travel across multiverses. He’s then invited to join the Council, an organization composed entirely of alternate versions of Reeds who operate outside of time and space for the betterment of the universes. The establishing of the Council of Reeds laid the groundwork for how Marvel conceives of and depicts its multiverse. In fact, the Hulk even has his own Council of Reeds. Given that the Marvel multiverse has made its way into the MCU, perhaps fans will see the Council on the big screen before long.

4 Mr. Fantastic Saves and Rebuilds the Entire Multiverse

2015’s Secret Wars #1 by Jonathan Hickman, Esad Ribić, Ive Svorcina, and Chris Eliopoulos showed Reed as a high-ranking contender for the most powerful Marvel hero when he saved and rebuilt the entire multiverse. When the multiverse was destroyed, only Battleworld was inhabitable, but it was ruled by a Molecule Man-powered Doctor Doom. After an intense face-off, Molecule Man instead gave Reed the mythological-like powers. His new power upgrade not only allowed him to destroy Battleworld and rebuild the entire multiverse, but also return his dead family to life — among other feats. The 2015 Secret Wars storyline introduced the concept of realities colliding with one another — known as “incursions” — to Marvel lore.

3 The Thing And Alicia Marry After Years Of Upheaval

The Thing’s love story with Alicia Masters was not always easy. Alicia being impersonated by a Skrull — who only had eyes for Johnny Storm — was just one of their many hardships. However, this on-and-off couple finally got back together after Ben Grimm was lost in grief when he thought Reed and Sue were dead. Ben proposed, and the pair finally made things official when they married in a small ceremony in 2018’s Fantastic Four #5 By Dan Slott, Michael Allred, Aaron Kuder, Adam Hughes, Marte Gracia, Laura Allred, Erick Arciniega, and Joe Caramagna. This event neatly tied up a long-running relationship plot line that fans were happy to see get a happy ending.

2 The Thing Adopts Two Children

Jo-Venn and N’Kalla are a Kree child soldier and a Skrull child soldier, respectively, who were adopted by the Thing and his wife Alicia in Empyre Fallout: Fantastic Four #1 by Dan Slott, Sean Izaakse, Marcio Menyz, and Joe Caramagna. When the Profiteer tries to take back control of the kids after they catalyze the Skrull-Kree alliance, the emperor of the alliance, Emperor Hulkling, squashes her plans and gives guardianship of the kids to the Thing. Jo-Venn and N’Kalla have become new members of the team (and family) who each have their own powers that they bring to the table. Both children are master combatants and chronicles of their species.

1 Franklin’s Full Powers Manifest

Franklin starts off with immense powers from a young age that continued to grow as he got older. He has a reality-warping ability and the power to manipulate matter — in addition to a number of psionic abilities. Numerous characters have spoken of Franklin’s unfathomably powerful abilities. To name just a few, Eternity and Infinity have cited Franklin as having powers on par with the Celestials. Examples of his fortitude include his healing of Galactus in Fantastic Four #604 by Jonathan Hickman, Steve Epting, Rick Magyar, Paul Mounts, and Clayton Cowles and his ability to create pocket universes. The abilities that he has had since a young age make him Marvel’s most powerful hero.

Title: The Extraordinary Life of Don Francisco de la Vega y Trujillo: Triumph Amidst Infamy

Introduction:
Born in 1799 into a noble Spanish family with a prestigious lineage that spanned centuries, Don Francisco de la Vega y Trujillo was destined for greatness. Nevertheless, his life took an unexpected turn when he became entangled in a scandal that precipitated an ultimatum: face the gallows or embark on a daring journey to the New World. This biography chronicles the remarkable story of how Don Francisco navigated treacherous waters and transformed adversity into triumph, leaving an indelible mark on history.

Early Life and Noble Heritage:
Don Francisco de la Vega y Trujillo was born into one of Spain’s most illustrious noble families on May 12, 1799. He hailed from an aristocratic bloodline deeply rooted in Spanish history, boasting ties to influential figures and important dynasties. His ancestors had played pivotal roles during the conquest of South America and held prominent positions within Spanish society.

Education and Prestigious Connections:
Don Francisco’s privileged upbringing facilitated access to quality education at esteemed institutions known for their emphasis on classical studies. Throughout his formative years, he distinguished himself as a diligent scholar with a sharp intellect. His academic prowess earned him recognition among his peers and faculty alike.

The Scandal:
Despite having all the privileges afforded by his noble birthright, fate dealt Don Francisco a bitter blow when he found himself embroiled in a scandal that threatened not only his reputation but also his very life. Details surrounding this unfortunate incident remain somewhat obscured by time; however, it is rumored that it involved allegations of covert espionage against the Spanish Crown.

Choosing the New World:
Faced with two equally grim choices—exile to the unfamiliar lands of the Americas or meeting an untimely demise at the hands of justice—Don Francisco exhibited astonishing courage by opting for the former. His decision to journey to the New World was fueled by a mix of desperation, determination, and an unwavering belief in his capacity to rebuild his life anew.

New Beginnings in the Americas:
In 1819, Don Francisco set sail across the vast Atlantic Ocean, leaving behind both his homeland and the comforts of a privileged existence. Arriving on unfamiliar shores shimmering with untapped potential, he dedicated himself to creating a fresh start from what seemed like insurmountable odds.

Adapting to Life in Exile:
Resilient and resourceful, Don Francisco leveraged his noble background and natural charisma as he endeavored to forge new alliances within Spanish American society. Drawing upon shrewd negotiation skills honed during his upbringing, he developed valuable connections with influential figures who recognized his talents.

Contributions and Legacy:
Don Francisco’s indomitable spirit brought forth numerous accomplishments over time. His keen intellect enabled him to engage actively in various intellectual circles of the time, sharing knowledge while simultaneously expanding his own horizons through encounters with great thinkers of the era.

A Melange of Cultural Fusion:
Furthermore, Don Francisco’s immersion into different cultures fostered an open-mindedness that allowed for greater appreciation of diversity. He became an avid patron of arts and letters within Spanish America—commissioning works from budding artists and cultivating relationships with renowned writers who were shaping this nascent post-colonial society.

Conclusion:
Don Francisco de la Vega y Trujillo’s journey from scandal-ridden nobleman to revered figure exemplified resilience under duress. By embracing exile rather than meeting a tragic end on his home soil, he transformed adversity into opportunity—pioneering new beginnings that ultimately shaped not only his own destiny but also left an indelible imprint on Spanish American history. Today, we honor Don Francisco as an emblematic figure whose remarkable story serves as a testament to endurance and redemption amid chaos.

Article number: 26.2.a29
https://doi.org/10.26879/1303
Copyright Paleontological Society, August 2023

Late Cenozoic rodent assemblages from western North America were added to a previous database limited to the central and eastern United States to develop a continental correlational system for the past 5 million years. Three hundred and twelve species representing 124 rodent assemblages were included, from which 12 Cenozoic Mammal Zones (CMZs) were constructed. Replacement chronologies for rodent assemblages based upon superposition, radiometric dates, paleomagnetic profiles, and evolutionary stages of dentitions from various depositional basins formed the skeleton for the chronological ordering of assemblages, and those lacking one or more information sources were sequenced based upon greatest concordance with available data. Arvicoline cricetids provided the most useful information for sequencing assemblages, followed by neotomine and sigmodontine cricetids and geomyids. The appearance of modern-sized cotton rats in CMZ 4, followed by the immigration of Allophaiomys across Beringia in CMZ 3, heralds the shift to the dominance of cotton rats and arhizodont voles in North American grassland ecosystems. No rapid bouts of significant turnover are associated with the beginning of the Pleistocene at 2.58 Ma (million years ago), but a pronounced turnover event was observed in the Meade Basin of southwestern Kansas immediately following the Huckleberry Ridge ash-fall at 2.07 Ma. Preliminary observations suggest two categories of rodent turnover; low-level background rotation determined by stochastic short-term regional and long-term global environmental change, and short-term turnover spikes mediated by catastrophic events such as volcanic eruptions.

Robert A. Martin. Department of Biological Sciences, Murray State University, Murray, Kentucky 42071, USA.
Thomas S. Kelly. Research Associate, Department of Vertebrate Paleontology, Natural History Museum of Los Angeles County, Los Angeles, California 90007, USA.

Keywords: North America, Neogene, Quaternary, mammal, rodent, biochronology

Final citation: Martin, Robert A. and Kelly, Thomas S. 2023. Biostratigraphy and biochronology of late Cenozoic North American rodent assemblages. Palaeontologia Electronica, 26(2):a29.
https://doi.org/10.26879/1303
palaeo-electronica.org/content/2023/3903-cenozoic-rodent-assemblages

Copyright: August 2023 Paleontological Society.
This is an open access article distributed under the terms of Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0), which permits users to copy and redistribute the material in any medium or format, provided it is not used for commercial purposes and the original author and source are credited, with indications if any changes are made.
creativecommons.org/licenses/by-nc-sa/4.0/

This study extends an earlier treatment of North American Late Neogene and Quaternary (~ last 5.0 My) fossil rodent assemblages from the eastern and central United States (Martin, 2019), adding regions of the continental United States, Canada and Mexico west of a line drawn roughly from western Texas north to western North Dakota (black line in Figure 1).

We recognize that in the future, paleontologists might choose to include other small or large mammal groups, and for that reason on the continental scale we have designated our categories as Cenozoic Mammal Zones (CMZs). Replacement chronologies for rodent assemblages based upon superposition, radiometric dates, paleomagnetic profiles, and evolutionary stages of dentitions from various depositional basins formed the skeleton for the chronological ordering of assemblages (Figure 2), and those lacking one or more information sources were sequenced based upon greatest concordance with available data. The use of many independently determined data sources minimized the amount of diachronism commonly associated with correlational unit boundaries (e.g., Ezquerro et al., 2022; Dam et al., 2023). Figure 1 provides locations of select pre-Rancholabrean rodent assemblages from the Supplementary Material table (color coding explained below). The primary purpose in developing a continental species-level rodent correlational scheme is to introduce into North American mammalian paleontology a system for the past five million years with at least the same refinement and utility as the MN/MQ Zones of Europe (Mein, 1975, 1976). A detailed chronology will provide a system within which mammalian assemblages without radiometric or paleomagnetic data may be tentatively sequenced and will consequently allow more accurate evaluation of mammal dispersal and evolutionary patterns.

Martin (2019) reviewed the history, benefits, and limitations of previous mammalian biochronologic/biostratigraphic systems in North America, including North American Land Mammal Ages (NALMAs) and various regional and taxonomic systems (Schultz et al., 1977, 1978; Lundelius et al., 1987; Martin, 1979, 2003; Repenning, 1987; Bell, 2000; Woodburne, 2004a, b; Bell et al., 2004), and these studies can be consulted for comparison. The most complete depositional sequence in North America for the later Cenozoic is the Meade Basin system of southwestern Kansas (Figure 2), and that sequence is used as a primary base reference for North American continental correlations. While the stratigraphic positions of the Meade Basin fossil localities have been resolved, because of a lack of radiometric dates beneath the Huckleberry Ridge ash at 2.07 Ma (Singer, 2014) and minimal paleomagnetic refinement beneath the Blancan Bender site, ages of assemblages from older Pliocene sites have been determined primarily by biostratigraphic correlation. A particularly difficult issue has been the placement of a series of sites on the north bank of the Cimarron River, including Wiens, Vasquez/Newt, XIT1B, Raptor IC, and Ripley. The stratigraphic relationships of these localities are clear (Honey et al., 2005), but their placement in time is uncertain because all the sites and associated sediments display reversed paleomagnetic signatures. An argument based on biostratigraphy and field mapping suggested that the sites noted above could be allocated to C3n.2r of the Gilbert chron, between 4.48-4.30 Ma (Marcolini et al., 2008; Martin and Peláez-Campomanes, 2014). Recently, Lukens et al. (2019) plotted this set of sites at a younger date, in C2ar, between 4.30-3.60 Ma. Consequently, it is imperative to also consult other systems noted in Supplementary Material and Figure 2 that may have older levels of the Meade Basin better constrained.

Despite the relatively complete Meade Basin and other Central Great Plains records, evidence is accumulating for a more complicated set of rodent dispersals with northern origins that may not be completely represented in the Meade Basin system and may be better represented in northwestern localities (e.g., Barnosky and Bell, 2004; Withnell et al., 2021). Also, because dispersal was generally from west to east, species appearances and durations in the western states differed from those in the Meade Basin. As in the case of Florida Pleistocene localities, there may have also been considerable regional endemism. Consequently, it will continue to be helpful to construct replacement chronologies from the depositional basin scale through continental geographic scales. An example application of a North American regional depositional system was a rodent replacement chronology developed for Florida (Martin, 2005) based in part on the work of Morgan and Hulbert (1995) and Morgan and White (1995). The recently published rodent chronology for the late Neogene of Spain (Dam et al., 2023) provides a blueprint for the application of many data sources to establishment of a regional biochronologic system.

MATERIALS AND METHODS

General Considerations

The difficulties associated with identifying CMZ boundaries primarily include problems with determining accurate depositional times for localities without radiometric dates and separated by considerable distance, sampling bias, taxonomic inaccuracies, and diachronic evolution (mosaic evolution) and dispersal. Attempts have been made to mitigate error by first establishing species replacement patterns in depositional sequences with radiometric dates and/or extensive paleomagnetic profiles (Figure 2). Dated immigration events provided further refinement, such as the Promimomys immigration event between 5.8-5.3 Ma (Martin, 2010; J. Martin et al., 2018) and the Allophaiomys immigration event at about 2.0 Ma (Martin et al., 2008). Entire species communities were consulted rather than relying on single species for correlational purposes; consequently, each CMZ is characterized by more than one taxon.

Following Tedford (1970), Woodburne (2004a, p. xiii) defines a “local fauna” as “An aggregate of fossil vertebrate species from a limited distribution in time from a number of closely grouped localities in a limited geographic area…. A local fauna could be based on taxa from a single locality.” Woodburne (2004a) also indicates that a “fauna” is often composed of a number of local faunas. We provide these definitions because there is considerable variation in the stratigraphic occurrence of species in Supplementary Material depending on collecting approaches. In the Meade Basin record, each named level represents a single quarry, generally no more than 1 m in depth, from which all identified species were collected. On the other hand, species in Supplementary Material from the Glenns Ferry Formation were collected from hundreds of localities along the Snake River in Idaho. We assume the resulting faunal associations can be roughly considered as communities extant during their respective intervals, and thus useful for biochronologic and biological comparisons because they are relatively consistent in composition, but some ambiguity must remain because of vertical dispersion of collecting localities and specimens collected as float. For reviews of paleontological work on the Glenns Ferry Formation, see Zakrzewski (1969), Neville et al. (1979), Conrad (1980), Repenning et al. (1995), Hart and Brueseke (1999), Sankey (1996), Hearst (1999), Ruez (2007, 2009), Walkup et al. (2016, 2021), and Prassack et al. (2021). In this paper the term “assemblage” is considered synonymous with both local fauna and locality, as the names of the assemblages are the same as the locality designations.

Species in Supplementary Material were taken from the literature, updated to modern taxonomic usage. In some cases, we used our personal experience to modify or question species determinations. We are preparing a study describing the Microtodon sp. noted in the Supplementary Material table for Hoye Canyon, Nevada. Supplementary Material includes full rodent assemblage records for select localities from North America, and the assemblage axis (columns) is color coded as follows: light green = west U.S., yellow = east U.S. NALMA boundaries, dated ashes and paleomagnetic events are identified in clear boxes, and significant faunal changes are identified by light tan boxes. Taxa from each assemblage are provided on the row axis, color-coded as follows: light green = west U.S., yellow = east U.S., and clear = recorded from both or unidentified to species. The column axis in Supplementary Material for the west U.S. begins with McKay Reservoir of Oregon and Hoye Canyon of Nevada, localities in the western group recording the Promimomys and Microtodon immigration events (Shotwell, 1956; Martin, 2010; J. Martin et al., 2018). Supplementary Material is meant to include enough assemblages to delimit broad CMZs to be used for correlational purposes, not to be exhaustive in locality or species coverage. We have not included the majority of late Pleistocene (Rancholabrean) assemblages, some of which undoubtedly include extant and possibly extinct species unrecorded in Supplementary Material (e.g., Wilson, 1967; Domning, 1969; Saunders, 1977; Graham et al., 1987; Jefferson, 1991; Jefferson et al., 1994, 2004; Gillette et al., 1999; Smith and Cifelli, 2000; Hill, 2001; Harington, 2009, 2011; Ferrusquía-Villafranca et al., 2010; Harris, 2014; Morgan and Harris, 2015). Many late Pleistocene cavern and sinkhole localities have produced rich rodent assemblages (e.g., Reddick [Gut and Ray, 1963] and other sites from Florida), but without radiometric dates, paleomagnetic profiles, or superpositional relationships with other sites it is unclear where they fit in the Late Pleistocene, and consequently they were omitted from Supplementary Material. Counting archeological sites, more than 100 late Pleistocene mammalian assemblages with extinct species are known from the Great Basin alone (Grayson, 2006). This treasure of data should be developed into an independent chronologically refined late Pleistocene database.

The Supplementary Material also includes the Little Sioux/Wright assemblages associated with the Lava Creek B (LCB) ash in Iowa. The latter was not covered in Martin (2019) and is included because it provides a rare glimpse of rodent diversity both above and beneath the same ash. The rodent records from Leisey Shell Pit, Florida (Morgan and White, 1995) and the Gilliland assemblage of Texas (Dalquest and Carpenter, 1988) were also added. Thomomys orientalis was added to the Coleman 2A, Florida, assemblage following Wilkins (1985).

Most of the rodent assemblages included in Supplementary Material are not bracketed by radiometric dates, although a few are found in proximity to a dated volcanic level. The majority of the assemblages are sequenced based on a few radiometric anchoring points, paleomagnetic profiles, evolutionary stages represented by rodent dentitions, and, where present, stratigraphic superposition. Paleomagnetic data are absent or limited for some sites, and the latter are sequenced exclusively on the rodent species represented in the larger context of continental data. Consequently, the order of assemblages listed in Supplementary Material within a given CMZ, unless including two or more assemblages with stratigraphic data (e.g., 111 Ranch [lower]; 111 Ranch [upper] or any of the Meade Basin sites) should not be considered as a confirmed chronological sequence. The LSDs (lowest stratigraphic datums) and HSDs (highest stratigraphic datums) in Figure 2 represent depositional basin records, not North American limits, although that may be the case as well. Unless determined from a radiometric date or coinciding with a paleomagnetic boundary, CMZ and boundary dates are approximations.

Many of the late Pleistocene assemblages derive from isolated sites, predominantly caves, sinkholes, and rock shelters. If open for long time periods and structurally complex, depositional patterns can be difficult to decipher. For example, only recently has it been determined that deposition at Natural Trap Cave, Wyoming, was discontinuous, with an almost 50 Ky (thousand year) hiatus between depositional regimes (Lovelace et al., 2022). Thus, Williams’ (2009) mammal species lists for levels 1-3 in Supplementary Material are now considered together as late Wisconsinan (< 25 Ka [thousand years ago]), and level 6 is considered pre – Wisconsinan and > 132 Ka. The species lists for levels 4 and 5 were lumped by Williams (2009) and omitted from Supplementary Material because they consist of a mixture of depositional periods. Additionally, radiocarbon dates may be limited in number and, if done many years ago, less accurate than more recent dating based on bone collagen. Consequently, the dates provided in Supplementary Material, taken from the literature, must be accepted with some caution. They have also been rounded to the nearest Ka or 0.1 Ka in Supplementary Material depending on precision of the original report. Likewise, the rodent species list compiled for San Josecito Cave from Nuevo Leon, Mexico, by Jakway (1958), has been refined based on new excavations revealing multiple temporal levels (Arroyo-Cabrales et al., 2021).

Index taxa are provided for each CMZ, but the list for a given zone may not be inclusive of all species in Supplementary Material limited to that zone. The taxonomy of certain clades, such as the sciurids and heteromyids, has not been revised lately, and we do not feel comfortable using many of these species to define rodent zones; likewise with some species of better-studied clades, such as Peromyscus within the cricetids. CMZ index taxa represent the most taxonomically stable and phylogenetically determined taxa in Supplementary Material with chronological value. Index taxa fall into one of two categories: 1) species limited to an CMZ (no parenthetical abbreviations) and 2) either LSD or HSD species for that zone. The combination must be unique to that CMZ. Due to the vagaries of sampling and chronological range, some CMZs may include more index taxa than others and, as noted above, not all LSD or HSD species in Supplementary Material are listed as index species.

The data in Table 1 were generated from Supplementary Material within the following guidelines: 1) generic records not identified to species (genus sp.) were counted in species tallies only if the record was the sole representative of its genus, and 2) species with chronomorphs (representing phyletic evolution) were identified by their species taxonomy when determining presence or absence in a given geographic region (e.g., Sigmodon bakeri /libitinus and S. bakeri /bakeri were counted once in the eastern USA).

Taxonomic Considerations

The effectiveness of a biostratigraphic/biochronologic system is dependent to a great extent on the taxonomic accuracy of the species identifications in its constituent database. The authors of this study have personally studied much of the material that forms the basis for the database, but we have not made comprehensive continental-wide comparisons among all rodent groups. In most cases, we relied on published regional analyses, our personal observations, and opinions of experts in certain rodent clades to construct Supplementary Material. Because arvicoline rodents figure prominently in late Neogene biochronology, it is important to explain our taxonomic approach and philosophy regarding this group to some extent.

The database includes the use of Martin’s (1993) chronomorphs, roughly equivalent to the lineage segments of Krishtalka and Stucky (1985), to identify intermediates in presumed phyletic sequences. The philosophy behind this usage and its comparison with the subspecies concept can be found in Martin (1993, 1995, 2019). Unlike lineage segments, chronomorphs may overlap in time, representing intraspecific mosaic evolution, as is commonly encountered in arvicolines, both fossil and Recent (Barnosky, 1993; Gordon, 1999; Marcolini and Martin, 2008). We treat phyletic change as evolution, and no matter how much morphological or size change is recorded, we recognize only a single species lineage. Speciation is considered a branching process, and in order for speciation to be identified both an ancestral and descendant species must be recognized as sympatric or at least synchronic. Nevertheless, in some cases, related allochronic species are maintained because the evidence is not sufficient to conclude they represent a phyletic series or there is considerable time between them. Species recognition, always dependent ultimately on expert recognition of synapomorphies, is based on published knowledge of dental morphology showing there is considerable local as well as geographic shape and size variation, especially in first lower molars (e.g., Guthrie, 1965; Guilday, 1982; Davis, 1987; Nadachowski, 1990; Martin, 1993; Rekovets and Nadachowski, 1995; Martin and O’Bryan, 2014). We base species recognition on the presence of synapomorphies, not percentages of molar morphotypes. For example, the dominant m1 morphotype in the Trout Cave No. 2 population of Pedomys is similar to the advanced m1 morphotype of the Java species, but more than 25% of the Trout Cave No. 2 m1s display the advanced morphotype characteristic of P. ochrogaster (Pfaff, 1990). Consequently, we view the Trout Cave population as an archaic population of P. ochrogaster recognized as P. o. /llanensis.

In a series of papers ending with his review of Mimomys (Repenning, 2003), the late Charles Repenning developed a taxonomic framework for North American arvicolines that allocated all extinct arvicolines with rhizodont molars and an occlusal pattern similar to that of Old World Mimomys to the latter genus. Repenning’s concept of Mimomys included taxa previously named as distinct genera, such as Cosomys, Ophiomys, and Ogmodontomys, plus two early Pleistocene species considered today to be correctly allocated to Mimomys, M. virginianus, and M. dakotaensis. Repenning (2003) reviewed the publication history of these taxa, and that will not be repeated here. We accept Repenning’s argument that generic identity should not be determined on continental allopatry alone. We also agree with Repenning (2003) that the occlusal molar morphology of the above North American taxa bear similarity to that of Old World Mimomys. If one were to place inordinate weight on the generality of that pattern, it is not difficult to see why Repenning considered them to be congeneric. However, detailed analyses of the microscopic enamel banding pattern of North American archaic arvicoline molars, the schmelzmuster of von Koenigswald (1980), demonstrate differences between the North American taxa and Old World Mimomys (Mou, 1998; von Koenigswald and Martin, 1984; Martin et al., 2006). Cosomys has three layers on both leading and trailing triangle edges of lower molars (opposite on uppers), with a lamellar enamel layer on the entire leading edge, showing that it developed the lamellar layer independently of Old World Mimomys that have only two layers on the leading edges when lamellar enamel is present (von Koenigswald, 1980). Ophiomys and Ogmodontomys never developed the full lamellar layer on the leading triangle edges, expressing only occasional lamellar patches (Mou, 1998; Martin et al., 2009). In addition to a well-developed lamellar layer on the leading edges of lower triangles and a tangential layer on the trailing edges, almost all Mimomys molars express negative enamel differentiation, with the trailing edges on the lowers (and leading edges on the uppers), thicker than their leading edges and, with the exception only of the most primitive recognized Mimomys, M. davakosi (= M. vandermeuleni; Hordijk and de Bruijn, 2009), added cementum in the reentrant folds. Cosomys, Ogmodontomys, and Ophiomys only have undifferentiated enamel and never express cementum. Additionally, in all Ophiomys, Cosomys, and Ogmodontomys atolls on M3 are rare or disappear with early wear, whereas in the Old World Mimomys that resemble North American archaic genera, such as Mimomys davakosi, one or often two atolls remain in all wear stages except the most senile specimens (van de Weerd, 1979; Hordijk and de Bruijn, 2009). Mimomys davakosi is the only Mimomys without cementum in the reentrant folds, and it is so similar in all dental features to Promimomys cor that Hordijk and de Bruijn (2009) noted that separating some specimens of each species found in the Ptolemais lignitic sequence of Greece was difficult. Despite the general resemblance in occlusal morphology of archaic North American arvicoline molars to those of Mimomys, we conclude there is compelling evidence that Ophiomys, Cosomys, and Ogmodontomys represent a separate New World clade of arvicolines, originating from one or two ancestral species such as Ophiomys mcknighti (Gustafson, 1978) or O. panacaensis (= Mimomys panacaensis, Mou, 1997). There remain legitimate different interpretations of the taxonomy of North American archaic arvicoline populations (e.g., how many Ophiomys species are present in North America; what is the correct assignment of the archaic arvicoline from the Upper Alturas locality of California [Repenning, 2003], etc.), but resolution of these problems will require further study.

Although only one species, Microtus deceitensis, is recorded from the Ft. Selkirk locality in Supplementary Material, specimens were recovered from beneath a dated ash, and thus provide evidence for an early appearance of a vole with arhizodont molars and a Microtus -like dental pattern. Microtus deceitensis and a sample of molars from Hamilton Cave in West Virginia were referred by Repenning and Grady (1988) and Repenning (1992) to Lasiopodomys deceitensis because of a similarity of m1 patterns, but this taxonomic assessment has been challenged by Storer (2003) and Alexeeva et al. (2015). We accept the position of extant arvicolines as a subfamily of the Cricetidae following Steppan and Schenk (2017) and Galewski et al. (2021).

In their review of fossil woodrats and relatives, Martin and Zakrzewski (2019) suggested that an extinct woodrat (Tribe Neotomini, Subtribe Neotomina) from the Hemphillian Rancho el Ocote assemblage of Mexico referred by Carranza-Castañeda and Walton (1992) to Neotoma (Paraneotoma) sp. might represent an early species of the extant Xenomys. As noted by Carranza-Castañeda and Walton (1992), the m1s available were from juveniles, and the m3 of this woodrat was not preserved. After further examination, without going into detail, we now consider the Xenomys attribution uncertain, and in Supplementary Material we refer to this taxon as Neotomina sp.

CMZ 12 (5.8 – 5.3 Ma)

Index taxa. Promimomys mimus, Microtodon n. sp., Protorepomys mckayi, Marmota korthi, Perognathus sargenti, Prodipodomys griggsorum, P. idahoensis (LSD), Onychomys (LSD), mylagaulids (HSD), Parapliosaccomys oregonensis (HSD), Repomys (LSD).

Characteristic assemblages. McKay Reservoir, Hoye Canyon, Mailbox, Zwiebel Channel.

Remarks. Arvicoline rodents first entered North America between 5.8-5.3 Ma (J. Martin et al., 2018) as Promimomys mimus (= Prosomys mimus) and dispersed from the west coast to the northern Great Plains in Nebraska (Voorhies, 1990). An arvicoline-like cricetid, Microtodon, also appears at this time. Both were quickly supplanted by the arvicoline tribe Pliophenacomyini, including Protopliophenacomys, Pliophenacomys, Guildayomys, and Pliolemmus (L. Martin, 1979; Zakrzewski, 1984; Martin, 2008). J. Martin et al. (2018) recently resurrected Shotwell’s (1956) Prosomys, and the taxonomic status of the McKay arvicoline needs to be reconsidered if, as Martin (2008) proposed, it is ancestral to the Pliophenacomyini. This radiation primarily took place on the Great Plains, as these genera are rare in the western states (Supplementary Material). No extant cricetid genera are recognized from this zone.

CMZ 11 (5.3 – 5.0 Ma)

Index taxa. Protopliophenacomys parkeri, Paenemarmota mexicana (LSD), Parapliosaccomys (HSD), Postcopemys (LSD); Pliogeomys carranzai, Prosigmodon oroscoi (LSD), P. chihuahuensis (LSD), Bensonomys elachys (LSD), B. baskini (LSD), Baiomys kolbi (LSD), Neotoma cf sawrockensis (LSD).

Characteristic assemblages. Santee, Yepómera.

Remarks. CMZ 11 is characterized by the first appearance of hypsodont, rhizodont geomyids (Pliogeomys), Protopliophenacomys parkeri, and a southwestern radiation of the extinct neotomine Bensonomys (Lindsay and Jacobs, 1985; Voorhies, 1990; Carranza-Casteñeda and Walton, 1992). The giant ground squirrel Paenemarmota mexicana first appears during this interval (McDonald et al., 2022).

Although Yepómera and Concha have a number of species in common, their respective localities are chronologically separated. Localities at Yepómera span most all the Thvera subchron (= C3n.4n) of the Gilbert chron with one locality (Y39) extending into an overlying reversed interval (= C3n.3r), just above the boundary between C3n.4n/C3n.3r, a total range of about 5.2-4.95 Ma (Lindsay et al 2006). Localities at Concha span the Sidufjall subchron (= C3n.3n) of the Gilbert chron from just below its boundary with C3n.3r to just above its boundary with C3n.3r, a total range of about 4.9 – 4.8 Ma (Lindsay et al. 2006). Notably, arvicolines are absent from Yepómera, which can in part be explained by its southern position, but also by the likelihood that the Pliophenacomyini had not extensively radiated by this time.

CMZ 10 (5.0 – 4.75 Ma)

Index taxa. Ophiomys panacaensis, O. mcknighti, Pliophenacomys wilsoni, Prosigmodon ferrusquiai, P. tecolotum, P. oroscoi (HSD), P. chihuahuaensis (HSD), Repomys gustelyi, Bensonomys winklerorum, Ammospermophilus hanfordi, Paenemarmota mexicana (HSD), Prothomomys warrensis, Baiomys kolbi (HSD), Jacobsomys dailyi (LSD), Geomys minor (LSD), Peromyscus (LSD).

Characteristic assemblages. Panaca, White Bluffs, Rancho el Ocote, Concha, Warren.

Remarks. CMZ 10 spans the Hemphillian – Blancan boundary at about 4.9 Ma (Lindsay et al., 2002) and is best characterized north of Mexico by the LSD for Ophiomys panacaensis from the Panaca Formation of Nevada (Mou, 2011) and O. mcknighti from the Ringold Formation of Washington state (Gustafson, 1978). These records, the first for Ophiomys in North America, are likely near the time of the Ophiomys immigration event from the Old World, and thus provide data points for our understanding of arvicoline evolution and dispersal. As observed by Repenning (2003), the first lower molar of Mimomys antiquus (Zazhigin, 1980) from Peshniovo 3, western Siberia, bears a strong resemblance to that of early Ophiomys, and according to Vasilyn et al. (2017) is assigned a date of about 4.9 Ma.

CMZ 10 is constrained in the Mexican sections that produced the Concha and Rancho el Ocote assemblages. Based on radiometric dates and paleomagnetic profiles, both the latter sections span almost the entirety of the Sidufjall subchron of the Gilbert chron (Lindsay et al., 2006) and extend to reversely magnetized sediments above. An advanced Pliophenacomys, P. wilsoni, is found at Concha, associated with many of the rodent species from the nearby, earlier Yepómera section. At Concha we see the last association of a Pliogeomys with early Geomys.

A new species of Prosigmodon, P. tecolotum, was recently described from the upper level of sediments in the Jalteco 26 section from the Tecolotlán Basin of Jalisco, central Mexico (Pacheco-Castro et al., 2019; Ronez et al., 2021). Very similar to other Prosigmodon species, it differs primarily in retaining a mesoloph on M1-M2, a plesiomorphic condition. This species was recovered from a lens in the section directly above an ash that was dated at 4.89 ± 0.16 Ma.

CMZ 9 (4.75 – 4.5 Ma)

Index taxa. Paenemarmota barbouri (LSD), Ogmodontomys sawrockensis, O. pipecreekensis, O. poaphagus (LSD), Pliophenacomys koenigswaldi, Bensonomys hershkovitzi, B. stirtoni, B. elachys (HSD), Symmetrodontomys daamsi, ?Ictidomys pipecreekensis, Otospermophilus rexroadensis (LSD).

Characteristic assemblages. Saw Rock Canyon, Pipe Creek Sinkhole, Fox Canyon.

Remarks. Ophiomys, Ogmodontomys, and Cosomys comprise the Ogmodontomyini (Martin, 2008; Marcolini et al., 2008), and both Ogmodontomys and Cosomys likely originated from Ophiomys as the latter genus spread eastward, eventually reaching the Central Great Plains. CMZ 9 represents the initial appearance of Ogmodontomys in Kansas and Indiana and further eastward dispersal and dental development in Pliophenacomys, expressed by P. koenigswaldi. In the Meade Basin, CMZ 9 also includes Fallen Angel B and Argonaut, both with Ogmodontomys sawrockensis, that lie above Saw Rock Canyon and beneath Fox Canyon (Martin and Peláez-Campomanes, 2014). Fallen Angel B and Argonaut have produced meager remains of a primitive sigmodontine that Peláez-Campomanes and Martin (2005) referred to Sigmodon sp., and Martin et al. (2021) referred to S. minor, but could also represent Prosigmodon. The earliest confirmed record of S. minor is in CMZ 8. Fox Canyon includes the first appearances of some common Pliocene rodents in the Meade Basin plus a dentally derived Ogmodontomys referable to O. poaphagus. Fox Canyon, like Saw Rock Canyon, lacks cotton rats.

CMZ 8 (4.5 – 3.9 Ma)

Index taxa. Sigmodon minor (LSD), S. holocuspis, Jacobsomys verdensis, Geomys anzensis, Perognathus strigipes, Postcopemys repenningi, Neotoma vaughani, Ellesmereomys haringtoni.

Characteristic assemblages. Ripley B, Verde (House Mountain Loc. 318), Raptor 1C, Wiens/Vasquez-Newt, Layer Cake, Strathcona.

Remarks. This zone includes the earliest North American appearances of Sigmodon minor, a characteristic Pliocene rodent, and a modern-sized cotton rat, Sigmodon holocuspis. Sigmodon cf minor is first encountered in the Meade Basin at Ripley B, lying above Fox Canyon and just above the Bishop Gravel, a characteristic early Pliocene marker bed. Sigmodon holocuspis was described from House Mountain Loc. 318 in the Verde Formation of Arizona, in magnetically reversed sediments referred to the Gilbert chron, between 4.48-4.29 Ma (Czaplewski, 1990). For reasons noted in Marcolini and Martin (2008), we tentatively conclude that House Mountain Loc. 318 and Raptor 1C were deposited towards the end of this reversal. S. holocuspis has only been recovered in the Meade Basin from Raptor 1C and a contemporaneous locality, Keefe Canyon (Peláez-Campomanes and Martin, 2005), and the evidence appears to indicate S. holocuspis had a brief geological lifespan in North America, providing a useful chronological anchor for part of the early Blancan.

Ruez and Gensler (2008) reported an unexpected discovery of Mictomys vetus, an extinct lemming, from a level in the Glenns Ferry Formation dated to about 3.93 Ma. Tesakov and Bondarev (2021) pointed out how unlikely this record was to be valid when compared to the evolutionary history of lemming dental features. Consequently, we do not include this record as an LSD for CMZ 8, awaiting further collections for corroboration.

The presence of Ellesmereomys haringtoni at Strathcona, on Ellesmere Island in the Canadian Arctic, documents the second North American record of a primitive arvicoline-like cricetid, bounded above by a cosmogenic nuclide date of 3.9 + 1.5/ – 0.5 Ma (Fletcher et al., 2019; Martin and Zakrzewski, 2022).

CMZ 7 (3.9 – 3.1 Ma)

Index taxa. Ophiomys taylori (LSD), Ondatra zibethicus /minor, Procastoroides intermedius, P. idahoensis, P. sweeti (LSD), Oregonomys magnus.

Characteristic assemblages. Hagerman, Sand Point, Taunton, Beck Ranch, Benson.

Remarks. Hagerman and Sand Point represent lower outcrops of a long Pliocene-Pleistocene rodent record in the Glenns Ferry Formation of Idaho (Figure 2) running from about 3.93 Ma to about 1.6 Ma. These sections crop out along the Snake River at various points (Zakrzewski, 1967; Repenning et al., 1995). Ophiomys taylori and Cosomys primus evolved from the earlier O. panacaensis/O. mcknighti evolutionary grade, and the earliest muskrats (Ondatra) and giant beavers (Procastoroides) appear during this interval. The last continental record of a geomyid with rooted molars (Pliogeomys) occurs at Hagerman. The LSD for Cosomys is in the Hagerman section, occurring beneath an ash bed of ca. 3.84 Ma (Figure 2; Hart and Brueseke, 1999; Ruez, 2009).

CMZ 6 (3.1 – 2.8 Ma)

Index taxa. Paenemarmota barbouri (HSD), Ondatra zibethicus /meadensis, Procastoroides sweeti (HSD), Ophiomys taylori (HSD), O. parvus (LSD), Nebraskomys rexroadensis, Pliophenacomys primaevus, Pliolemmus antiquus (LSD), Hibbardomys skinneri, Geomys quinni (LSD).

Characteristic assemblages. Rexroad Loc. 3, Sand Draw, Deer Park, Birch Creek, Boyle Ditch, Mesa del Sol, Blanco.

Remarks. Nebraskomys (ancestral to the Pleistocene Atopomys), Pliolemmus, and Hibbardomys appear during CMZ 6. The relationships of Hibbardomys are obscure, but there is some resemblance of the Hibbardomys dentition to that of Phenacomys, and Martin (2008) included both in the arvicoline tribe Phenacomyini. Symmetrodontomys, Pliolemmus, and Ogmodontomys become extinct before CMZ 5. Ondatra zibethicus /meadensis is the characteristic muskrat chronomorph of CMZ 6. Ophiomys parvus originates from O. taylori in CMZ 6.

In their description of the new Zwiebel Channel Hemphillian locality from the Sand Draw area of Nebraska, Martin et al. (2017) suggested that localities with Ophiomys (e.g., O. magilli from UM Loc. 3-67) occurred higher in the stratigraphic section of the Sand Draw area than sites with Ogmodontomys poaphagus. Although there may be some stratigraphic differences in species occurrences, we now consider O. magilli a slightly advanced form of O. taylori, and the rodents from all localities listed by Hibbard (1972) from the Sand Draw region of Nebraska to be roughly equivalent in age to other localities with Pliolemmus, Nebraskomys, and Ogmodontomys poaphagus, such as Deer Park, Kansas.

CMZ 5 (2.8 – 2.2 Ma)

Index taxa. Thomomys carsonensis, Ondatra zibethicus /idahoensis, Ophiomys parvus (LSD), O. meadensis (LSD), Pliophenacomys osborni (LSD), Repomys arizonensis, Geomys floralindae (LSD).

Characteristic assemblages. Flatiron Butte, Grand View, 111 Ranch, Arroyo Seco, Sanders.

Remarks. This interval is characterized by the first appearance of Ondatra zibethicus /idahoensis, a chronomorph of the North American muskrat larger in size than O. z. /meadensis and with the first evidence of cementum in reentrant folds. There is also an increase in dental complexity in Ophiomys, leading from the last record of O. taylori at Flatiron Butte, ID to O. parvus at the Grand View/Ninefoot Rapids level (Conrad, 1980). A slightly more advanced Ophiomys currently recognized as O. meadensis appears during CMZ 5 on the Great Plains in Texas and Kansas.

CMZ 5 also includes the cold period that begins the Pleistocene epoch at 2.58 Ma. Although rodent species turnover and some evolutionary changes are observed, this does not seem to be a particularly dramatic period of flux as compared with, for example, change seen on the Central Great Plains in the Meade Basin following the Huckleberry Ridge ash-fall at 2.07 Ma (see Discussion).

CMZ 4 (2.2 – 2.0 Ma)

Index taxa. Geomys floralindae (HSD), Sigmodon hudspethensis, S. curtisi (LSD), Ophiomys meadensis (HSD), Plioctomys rinkeri, Hibbardomys fayae, H. voorhiesi, Reynoldsomys timoteoensis, Plioctomys rinkeri, Pliolemmus antiquus (HSD), Zapus sandersi (HSD).

Characteristic assemblages. Hudspeth, Cita Canyon, San Timoteo, Curtis Ranch, Borchers, Froman Ferry, Inglis 1A.

Remarks. CMZ 4 is characterized by the appearance of modern-sized cotton rats with advanced occlusal patterns, S. hudspethensis and S. curtisi (Strain, 1966; Akersten, 1970). Almost all the holdover “Pliocene fauna” of Great Plains rodents becomes extinct during this interval, mostly near its end, following the Huckleberry Ridge ash-fall at 2.07 Ma. With the exception of the immigration of Mimomys in CMZ 3, this interval represents the end of dominance in North America of arvicoline rodents with rooted molars. Myodes and Ondatra are the only extant rhizodont arvicolines, the former restricted to forest ecosystems and the latter to aquatic habitats.

CMZ 3 (2.0 – 1.29 Ma)

Index taxa. Ondatra zibethicus /annectens (LSD), Allophaiomys sp., Pedomys n. sp., Tyrranomys harkseni, Javazapus weeksi, Mimomys virginianus, M. dakotaensis, Atopomys texensis, Microtus (LSD).

Characteristic assemblages. Java, Short Haul, Aries A, Hamilton Cave, SAM Cave, Fyllan Cave, Sappa.

Remarks. This interval is well represented and constrained in the Meade Basin by several localities, radiometric dates, paleomagnetism, and biostratigraphy. The Allophaiomys immigration event across Beringia is considered to have occurred around 2.0 Ma, and defines the base of the Irvingtonian NALMA (Martin et al., 2008). This event represents the first wave of dispersal from Asia of arhizodont arvicoline rodents destined to become the dominant small grassland herbivores, later represented by various species of Microtus, Pedomys and Pitymys. A single m3 of an arhizodont arvicoline was recovered from a geologic core just above the Huckleberry Ridge ash (2.07 Ma) at Hansen Bluff, Colorado (Rogers et al. 1992). The age was estimated at about 1.89 Ma. While at this period of time the most likely arhizodont arvicoline with the m3 morphology illustrated by Rogers et al. (1992; fig. 9) would be Allophaiomys, identification cannot be made solely on the morphology of m3. Until records of Allophaiomys from Little Dell Dam, Utah (Gillette et al., 1999) and SAM Cave, Colorado (Rogers et al., 2000) can be confirmed with additional specimens or illustrations, Allophaiomys is otherwise absent from western sites prior to its appearance at Porcupine Cave in CMZ 2. This absence could be considered sampling bias, except that Allophaiomys has not been recovered from the San Timoteo, Glenns Ferry, Vallecito-Fish Creek, or San Pedro Valley lengthy sequences, and thus appears have first dispersed eastward through North America by a northern route, bypassing both the Rocky Mountain chain and arid western ecosystems. Later, perhaps during glacial advances, Allophaiomys moved briefly into some western states, mostly at high elevation. Atopomys texensis, an arvicoline descended from Nebraskomys, appears during this interval, associated with Allophaiomys at Fyllan Cave, Texas (Winkler and Grady, 1990; Winkler and Gose, 2003). The new species of Pedomys from Java listed in Supplementary Material includes many m1s with simple Allophaiomys morphotypes and thus likely represents a common ancestor for later North American Pedomys species.

An interesting combination of arvicolines is found at Hamilton Cave, West Virginia (Repenning and Grady, 1988; Repenning, 1992). The arhizodont component may include two or three species, one of which may be an early Pitymys retaining some Allophaiomys m1 morphotypes. If this identification is confirmed, the Hamilton Cave Pitymys could represent an ancestral grade for both later extinct and extant Pitymys.

The North American muskrat increases in size and becomes recognized as Ondatra zibethicus /annectens, extending through CMZ 2. The earliest record of the modern Great Plains Pocket Gopher, Geomys bursarius, is from this interval in the Meade Basin of Kansas (Martin et al., 2011; Martin, 2016). CMZ 3 is bounded on the young side by the Mesa Falls ash-fall from the Yellowstone caldera (Lanphere et al., 2002), correlative with the Coleridge ash of Nebraska (Boellstorff, 1978), directly overlying the Sappa local fauna of Kansas.

CMZ 2 (1.29 – 0.30 Ma)

Index taxa. Ondatra zibethicus /annectens (HSD), Microtus meadensis (HSD), M. paroperarius (HSD), M. morlani, Pedomys guildayi, P. australis, P. ochrogaster /llanensis (HSD), P. o. /ochrogaster (LSD), Pitymys aratai, P. cumberlandensis.

Characteristic assemblages. Hansen Bluff, Haile 16A, Cumberland Cave, Thistle Creek, Cudahy, Vera, Conard Fissure, Port Kennedy, Coleman 2A.

Remarks. This interval is characterized by an almost bewildering array of small arhizodont arvicolines, representing a combination of autochthonous radiations and continued dispersals across Beringia. Allophaiomys splits into the Pedomys complex, beginning with P. guildayi, P. australis, and P. ochrogaster, and the characteristic middle Pleistocene species Microtus paroperarius and M. meadensis first appear (Hibbard, 1944; Paulson, 1961; Martin, 1995). Microtus deceitensis and those earliest Microtus m1 specimens reported in the literature as displaying either the paroperarius or Lasiopodomys m1 morphotype (as at Hamilton Cave; Repenning and Grady [1988]), are variants of the pattern seen in the extant Alexandromys oeconomus, in which the anteroconid complex is asymmetrical, T 4-5 are alternate, LRA 4 is well-developed, BRA 3 is often shallow, and BRA 4 ranges from absent to modestly developed but usually without cementum when it is present (Figure 3). A. oeconomus (= Microtus operarius; hence M. paroperarius for the extinct species) is a tundra-steppe species, and fossil Microtus-like m1s with the paroperarius m1 morphotype tend to be found in the far north (Fort Selkirk, Yukon; Cape Deceit, Alaska), in mountain chain cavern localities (Hamilton Cave, WV; Porcupine Cave, CO), or on the Central Great Plains (Cudahy, KS; Vera, TX, etc.) only during glacial intervals, suggesting these species represent a distinct clade with northern origins, perhaps Alexandromys, separate from other Microtus (such as M. pennsylvanicus) that may also have had a northern origin, but at a later time, and are more temperate-adapted. It is instructive that cotton rats, genus Sigmodon, are absent from fossil localities with the M. paroperarius-like m1 morphotype throughout the continent, further supporting the hypothesis that species with an M. poaroperarius -like dental morphology represent a clade with northern environmental preferences.

In North America the earliest record of a Microtus species not referable to either the paroperarius group or M. meadensis is from Porcupine Cave, Colorado. Illustrations of this taxon, identified as Microtus sp., were provided by Bell and Barnosky (2000), and are similar to Microtus pennsylvanicus m1s with five triangles. Numerous molars from this species were recovered. The vast majority of Microtus sp. specimens (104/128 = 81%) were recovered from levels 1-2 in the Pit controlled excavations. Microtus meadensis specimens were also excavated from the same levels. A few M. paroperarius m1s were scattered relatively evenly through the first two levels. Allophaiomys pliocaenicus molars were found only in levels 4-6. Barnosky (2004) recognized this difference in relative abundance, and identified two depositional zones. He estimated the age of the Microtus sp. zone to at >0.60 – < 0.85 Ma and the Allophaiomys zone >0.78 – 1.0 Ma. Other records of this association, such as at Little Dell Dam locality in Utah (Gillette et al., 1999), SAM Cave, Colorado (Rogers et al., 2000), Hamilton Cave in West Virginia (Repenning and Grady, 1988) or Cathedral Cave, Nevada (Jass and Bell, 2011) cannot be confirmed based on published information.

The oldest association of Microtus paroperarius and M. meadensis may be from Hansen Bluff in Colorado, from sediments directly above the Bishop ash at 0.76 Ma (Rogers et al., 1985, 1992; Sarna-Wojcicki et. al., 2000). However, M. meadensis was recovered lower in the sections than M. paroperarius, and there could be as much as 50 thousand years between the levels. On the Central Great Plains these species are found together in a number of localities directly underneath the Lava Creek B ash at 0.64 Ma (Lanphere et al., 2002; Schultz, 2010). In none has a more advanced Microtus been securely documented; thus it appears Microtus pennsylvanicus, the dominant extant Microtus on the Great Plains, had not reached that region by 0.64 Ma, further suggesting that fossil Microtus morphologically referable to modern species from Porcupine Cave and elsewhere in the western United States are not likely much older than 0.64 Ma. The youngest records of Microtus paroperarius and M. meadensis may be from Salamander Cave in the Black Hills of South Dakota (Mead et al., 1993). Uranium series dates suggest a range from 0.15-0.45 Ma, and three of the four authors concluded they preferred a depositional date for the majority of the fossils at 0.25 Ma based on a Th/Pa ratio from an Equus phalanx from the main bone bed, while one of the authors (C.A. Repenning) preferred a date closer to 0.60 Ma based on previously known biochronology of the Salamander Cave arvicolines.

Continuing with the arvicolines, the earliest Pitymys, P. cumberlandensis, appears at Cumberland Cave, Maryland (van der Meulen, 1978). New U-series Electron Spin resonance dates from Cumberland Cave provided dates of 722 and 790 Ka for the deposits (Withnell et al., 2020). A middle Pleistocene Pitymys radiation apparently followed, culminating with the late Pleistocene P. aratai (Martin, 1974) and modern P. pinetorum and Mexican species such as P. quasiater (Martin, 1995). It is not likely P. cumberlandensis was ancestral to later pine vole species (Martin, 2014), but the Hamilton Cave populations mentioned in CMZ 3 could represent that evolutionary grade.

CMZ 1 (0.30 – 0.001 Ma)

Index taxa. Microtus pennsylvanicus (LSD), Pedomys parmaleei, dominance of modern species.

Characteristic assemblages. Kennewick, San Josecito Cave, Papago Springs Cave, Jinglebob, Cragin Quarry, Dry Cave, Natural Trap Cave, Jones.

Remarks. Microtus referable to modern species do not appear until the late Pleistocene, and because the timing of the modern Microtus radiation apparently began between the Lava Creek B ash-fall and the first radiocarbon-dated assemblages about 50 Ka, we have no trustworthy dates for this interval. A search for species of Pleistocene Microtus in the Neotoma (FAUNMAP) database reveals no published records prior to a flurry of specimens from extant species reported from localities younger than the 0.64 Ma Lava Creek B ash. Microtus, Pedomys, and Pitymys species become common components of North American late Pleistocene faunas, particularly during the Rancholabrean NALMA, and in the central and eastern states the most common species are the extant Microtus pennsylvanicus, Pedomys ochrogaster, and Pitymys pinetorum and the extinct Pedomys parmaleei. As noted by Murray et al. (2011) in the western states there are a number of Microtus species with overlapping dental morphology, and thus identification to species is often difficult. Nevertheless, extant species dominate Rancholabrean sites. From these observations we can generalize that the radiation of continental North American Microtus (not including Pitymys and Pedomys) into extant species likely began no earlier than the middle Pleistocene about 0.70 Ma, but the details of this radiation remain unknown.

On the Central Great Plains a regional rodent zone can be distinguished at 0.64 Ma, coincident with Lava Creek B ash deposition, because a number of rodent assemblages in Kansas and Texas with comparable rodent communities have been recovered from directly beneath this ash (Martin, 2019). None contain Allophaiomys, and it seems clear Allophaiomys had evolved into early Pedomys by this time, as the assemblages include Pedomys ochrogaster/llanensis (Supplementary Material). Extant populations and late Pleistocene samples of Pedomys ochrogaster occasionally display Allophaiomys m1 morphotypes (Harris, 1988; Martin, 1991). As noted above, Allophaiomys is rare in western North America, and its chronology there is not well constrained. Although deposits of Lava Creek B ash are found commonly in the western states, no rodent assemblages have been reported associated with them, and there is no record of extant or extinct Pedomys in western states prior to the late Pleistocene. These observations demonstrate the value of both regional and continental rodent databases in determining distributional and evolutionary patterns.

Table 1 provides a rough geographic breakdown of the 312 species in Supplementary Material. The list does not include many late Pleistocene sites and therefore many extant species. Nevertheless, the “pull of the Recent” probably produces a certain degree of bias. The totals, therefore, represent only a crude estimate of regional species richness over the last 5 million years, and should be examined chronologically to illuminate both regional and continental diversity dynamics. Western states appear to have had a greater richness of cricetids and heteromyids, and the absence of heteromyids from eastern states even during periods of aridity in which there was likely at least a patchy, arid corridor connecting Texas with the Gulf states (e.g., the late Irvingtonian Coleman 2A assemblage from Florida with Thomomys, Lepus, Conepatus, Felis onca, and Hydrochoerus; Martin, 1974; Wilkins, 1985), suggests heteromyids were limited throughout the late Cenozoic to the Great Plains and points west. Neotominin cricetid diversity (e.g., Neotoma, Repomys) has been consistently higher in western than central or eastern North America.

As noted above under CMZ 5, this interval spans the currently recognized beginning of the Pleistocene epoch at 2.58 Ma, also the base of the Matuyama chron. A logical question is to what extent the beginning of the Pleistocene affected rodent biogeography and evolution. The answer is probably best addressed through regional depositional basins where the base of the Matuyama paleomagnetic chron is recognized or assumed to be present because this boundary is roughly contemporaneous with the beginning of the Pleistocene. In North America basins spanning that time with superposed rodent assemblages are limited, but those available do not demonstrate enhanced rates of rodent species turnover at the advent of the Pleistocene, though changes in other mammal groups may provide additional information. In the extensive Vallecito-Fish Creek (VFC) sequence of southern California (Cassiliano, 1999), change in the rodent contingent above the onset of the Pleistocene is limited only to the appearance of a large cotton rat, Sigmodon lindsayi and, at the top of the sequence, a Microtus near M. deceitensis (with a likely northern origin). In the VFC sequence there are some notable early Pleistocene shifts in other mammal groups, including extinction of ancient lagomorphs such as Hypolagus and Nekrolagus and the appearance of Sylvilagus. The sloths, Megalonyx, Nothrotheriops, and Glossotherium first appear almost coeval with the base of the Matuyama. However, these are not new South American immigrants, as Megalonyx is likely a descendant of the much earlier immigrant Pliometanastes (Morgan, 2005), and Glossotherium was present in Mexico 4.6-4.8 Ma (Carranza-Casteñeda and Miller, 2004). Nothrotheriops is an Irvingtonian immigrant, appearing in North America about 1.3 Ma at Leisey 1A in Florida (McDonald, 1995).

In the western and Great Plains states, many characteristic Pliocene species, such as Sigmodon minor, Bensonomys arizonae, Prodipodomys idahoensis, and Pliophenacomys osborni, continue through CMZ 5 into CMZ 4. Unfortunately, only the Sanders assemblage in the Meade Basin of Kansas lies at the approximate base of the Matuyama/earliest Pleistocene boundary and its rodent contingent is sparse. Notably present is the advanced arvicoline Ophiomys meadensis, replacing the earlier Ogmodontomys poaphagus, but there is an absence of fossil localities between Sanders and Margaret, the latter lying beneath Borchers and the Huckleberry Ridge ash (older than 2.07 Ma). In the Duncan Basin of Arizona, the 111 Ranch rodent sequence extends from the end of the Gauss through the early Matuyama chrons. Tomida (1987) conveniently broke the faunal list into lower (presumably prior to the Gauss-Matuyama boundary) and upper units. Other than the disappearance of Repomys arizonae and Pliophenacomys primaevus from the lower level, both representing global extinctions, there is little difference between the two assemblages. The lemming Mictomys vetus is limited to the lower beds, but it is a common element of younger continental deposits elsewhere, so it is difficult to ascribe any particular significance to its absence in the upper quarries.

Circumstantial evidence suggests there are at least two categories of rodent species turnover in North America. The first, which we can label background turnover, is a relatively low, constant rate driven primarily by Milankovich cycles and stochastic regional climate changes (Martin and Peláez-Campomanes, 2014). Second category events are short-term catastrophic environmental changes on either a global or regional scale, including massive floods and volcanic eruptions. In the Meade Basin rodent record over the past five million years, background turnover averages < 2 E/ or I/MSY (extinctions or immigrations/million species years; Martin and Peláez-Campomanes, 2016). Category 2 is represented by the Huckleberry Ridge and Lava Creek B ash-falls at 2.07 and 0.64 Ma. Between Borchers at 2.07 Ma and Aries A at ~2.0 Ma, 40% of the Meade Basin rodent community turned over. A small part of the change appears to represent cladogenesis, as both the modern Ictidomys tridecemlineatus and Geomys bursarius appear soon after the Huckleberry Ridge deposition (Martin et al., 2021). There is a depositional hiatus between about 1.35-0.64 Ma and a lack of dates for localities from 0.64 Ma to the first radiocarbon-dated sites in the Meade Basin, so we cannot precisely determine turnover rates during these periods, but it is clear the modern rodent community of the Meade Basin area was mostly established by the middle late Pleistocene (e.g., Kanopolis, Berends, Doby Springs; Supplementary Material), in perhaps a period of ~100 – 200 Ka following the Lava Creek B ash-fall. A research program designed to sample for rodent communities above and beneath dated ashes could test the ash-fall hypothesis and, concomitantly, provide better chronological control to the continental system.

Arvicoline Diversity

The database of Supplementary Material can be used to examine a number of evolutionary and distributional questions. We provide an example with a preliminary evaluation of North American arvicoline diversity from Supplementary Material over the past five million years. Figure 4 presents a graph of this diversity. Numbers of species on the ordinate were plotted against midpoints of CMZs in Ma on the abcissa. Because species numbers in CMZ 1-2 are affected so greatly by the number of Rancholabrean assemblages tallied, we omitted the total for CMZ 1; the tally for CMZ 2 should be considered only as a rough approximation, but an indication of a significant rise over CMZ 3. The data were best fit by an exponential function. Increase in numbers was modest through most of the Pliocene and early Pleistocene, comprised mostly of rhizodont extinct taxa such as Ophiomys, Ogmodontomys, Cosomys, Pliophenaomys, Hibbardomys, Nevadomys, Nebraskomys, and Plioctomys. As observed above, no elevated arvicoline turnover events characterize the advent of the Pleistocene at 2.58 Ma. All the archaic, mostly rhizodont arvicolines became extinct by the end of CMZ 3. CMZ 4, a brief interval between 2.2-2.0 Ma, includes the Huckleberry Ridge (HR) ash-fall at 2.07 Ma and the subsequent Allophaiomys immigration event documented in the Meade Basin of Kansas. Elsewhere in North America, roughly at the same time, the LSDs for Phenacomys and Mimomys are encountered. These observations are consistent with a glacial scenario bringing new arvicolines into North America via a northern route at a time when much of the central and western USA had been devastated by the HR ash-fall. However, only cotton rats have been recovered in the Meade Basin prior to and just following the HR event (Margaret/beneath, Borchers/immediately above; Martin et al., 2021), and it is therefore likely that the archaic arvicolines such as Hibbardomys, Pliophenacomys and Ophiomys, were extinct by that time. That is, although no punctuational turnover was observed at the beginning of the Pleistocene, early Pleistocene environmental change may have gradually hastened the demise of archaic arvicolines prior to the HR ash-fall.

Although North American Allophaiomys may be ancestral to both Pedomys and Pitymys, arvicoline diversity increased little in CMZ 3. By CMZ 2, one or more dispersal events across Beringia introduced a number of new Microtus clades, including M. meadensis and a group of species related to M. paroperarius, the latter with northern affinities. New Pedomys and Pitymys species and modern lemming genera appeared. Extant species of Microtus are recorded from many North American sites in CMZ 1, probably representing a combination of late Pleistocene Beringian immigrants and phylogenetic radiation from CMZ 2 ancestors. Concomitantly, large cotton rats, genus Sigmodon, diversified and spread into austroriparian prairie habitats in southern North America and northern South America. From that time onward, arhizodont voles and cotton rats become the dominant small pastoral herbivores in global Holarctic ecosystems.

A database of rodent species communities for the past five million years is extended from the eastern and central United States (Martin, 2019) to include all of North America. This new correlational scheme, including 312 species from 124 communities, allows recognition of 12 Cenozoic Mammal Zones (CMZs), each defined on the basis of a series of index taxa. Turnover in the arvicoline cricetids, followed by neotomine and sigmodontine cricetids and geomyids, provided the most useful information. Further taxonomic study, particularly with the sciurids, heteromyids, and cricetids, will continue to refine the database and its conclusions. Preliminary examination of the data indicate no rapid bouts of rodent turnover at the Pliocene-Pleistocene boundary about 2.6 Ma, but a pronounced turnover event is recorded in the Meade Basin of Kansas following the Huckleberry Ridge ash-fall at 2.07 Ma. Arvicoline diversity is best modeled by an exponential curve, identifying a late Pleistocene surge in species diversity.

ACKNOWLEDGMENTS

This North American rodent database is the result of field and lab research by many colleagues, and we thank them all for their contributions. In particular, we are grateful for the pioneering work by E.H. Lindsay on fossil rodent phylogeny and the introduction of screen-washing to paleontology by C.W. Hibbard, whose concentrated fieldwork in the Meade Basin of Kansas, along with that of his students, established a biostratigraphic framework for the Central Great Plains. We also appreciate the comments by two anonymous reviewers.

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The nickel market is expected to undergo a significant shift in the coming years as the global energy transition speeds up. Currently, only about 11 per cent of nickel goes towards the electric veh…

DULUTH — Two-term Mayor Emily Larson and former Minnesota lawmaker Roger Reinert advance to the Nov. 7 general election, in Duluth’s first competitive mayoral race in 16 years.

Reinert received about two-thirds of the vote at 63%, with Larson, the city’s first female leader, capturing just over a third, according to unofficial results from the Office of the Minnesota Secretary of State.

The other three candidates captured about 2% of the votes combined. About a quarter of the 54,000 registered voters in Duluth cast a ballot for mayor Tuesday.

The cost and availability of housing, ire with the current administration and, of course, potholes all drove Duluthians to the polls Tuesday in the only municipal primary election held in Minnesota.

Lincoln Park resident Tracy Curnow typically doesn’t vote in primary elections, “but this year I just feel so strongly.”

The cost of renting in Duluth has gotten “outrageously expensive,” and she’s hoping a Reinert win would mean change.

“It’s time to have someone new step in,” Curnow said.

Unhappiness with Larson is what spurred western Duluth resident Brian Wark to vote, he said, with the city too focused on tourism and not enough on its residents.

“This town has gone too far,” he said. “Get this mayor out of here.”

Some residents sought to re-elect Larson for prioritizing the environment and protecting the city’s most vulnerable populations.

Sonja Englund, who voted for Larson in eastern Duluth, said she’s happy with Larson’s efforts to reduce climate change and make the city a more welcoming place.

“We have been such a great safe haven,” she said.

Lincoln Park’s Matt Oman said Larson “knows what she’s doing” and felt comfortable electing her to a third term.

Lots of voters didn’t want to disclose whom they chose to lead the city, citing the similarities of Larson’s and Reinert’s platforms and Duluth’s small-town nature.

Kris Kolenz, voting near the University of Minnesota Duluth, said she went back and forth between the two.

“What a good thing to have two good candidates,” she said.

Larson, a social worker who has served on Duluth’s City Council, received endorsements from the Duluth DFL and Gov. Tim Walz. Reinert, a member of the U.S. Navy Reserve and a former Duluth City Councilor who has served in both houses in the state Legislature, snagged the support of the city’s police and firefighter unions. (Reinert announced in May he would not seek the DFL endorsement, after initially pursuing it.)

The two are close in fundraising: Roughly $47,000 has been donated to Reinert and $53,000 to Larson through the end of July. Larson easily outraised each of her opponents in the 2015 and 2019 elections.

Incumbent Arik Forsman, Lynn Nephew, Jenna Yeakle and Miranda Pacheco will compete for two City Council at-large seats, out of a pool of eight. Forsman was the top vote-getter with 29%.

The city’s elected officials need to strike a balance between preserving Duluth’s natural resources and attracting new businesses, said Lisa Wentworth, voting in Duluth’s northern Kenwood neighborhood. She chose Forsman for his ability to do that, she said.

“Arik has a great heart for Duluth, and balances that well with being business-minded,” Wentworth said.

Advancing in the City Council fourth district race are Tara Swenson and Howie Hanson, narrowly edging out Salaam Witherspoon.

Henry Banks and Loren Martell, who have both run for Duluth School Board seats previously, will compete for the board’s third district seat.

Staff writer Christa Lawler contributed to this story.