Two new pocket mice (Mammalia, Rodentia, ) from the Miocene of Nebraska and New Mexico and the early evolution of the subfamily Perognathinae

William W. KORTH Rochester Institute of Vertebrate Paleontology, 265 Carling Rd., Rochester, New York 14610 (USA) [email protected]

Korth W. W. 2008. — Two new pocket mice (Mammalia, Rodentia, Heteromyidae) from the Miocene of Nebraska and New Mexico and the early evolution of the subfamily Perogna- thinae. Geodiversitas 30 (3) : 593-609.

ABSTRACT Two new genera and species of heteromyid are described: Eochaeto dipus asulcatus n. gen., n. sp. from the late Arikareean (earliest Miocene) of Nebraska and Mioperognathus willardi n. gen., n. sp. from the Barstovian (middle Mio- cene) of New Mexico. Eochaetodipus asulcatus n. gen., n. sp. is based on a nearly complete skull with associated mandibles and some postcranial material. Th is specimen is the earliest recognized member of the subfamily Perognathinae based on shared cranial and skeletal features with extant perognathines (mas- toid infl ation; reduction of incisive foramina; separation of the buccinator and masticatory foramina; more gracile skeleton). Eochaetodipus n. gen. is viewed as more primitive than other perognathines because it lacks a number of derived features of the latter. Th e cranium of Mioperognathus n. gen. was previously described as “Perognathus minutus”. It diff ers from that of Eochaeto dipus in a KEY WORDS number of features that are considered derived for perognathines (loss of the Mammalia, Rodentia, accessory foramen ovale; greater infl ation of the bulla and mastoid; reduction Heteromyidae, of the squamosal dorsal to the external acoustic meatus to a thin bar; presence Perognathinae, cranial foramina, of an unossifed area on the orbital wall; grooved upper incisors), but is distinct Barstovian, from extant perognathines in several characters interpreted as primitive (presence Arikareean, of temporal foramen; less infl ated bulla; longer temporalis scar). A phylogenetic Miocene new genera, analysis shows that the perognathine clade arose from a mioheteromyine-like new species. ancestor separate from the Heteromyinae.

GEODIVERSITAS • 2008 • 30 (3) © Publications Scientifi ques du Muséum national d’Histoire naturelle, Paris. www.geodiversitas.com 593 Korth W. W.

RÉSUMÉ Deux nouvelles souris à poches (Mammalia, Rodentia, Heteromyidae) du Nebraska et du Nouveau-Mexique du Miocène et évolution primitive de la sous-famille Perognathinae. Deux nouveaux genres et espèces de rongeurs Heteromyidae sont décrits : Eochaeto- dipus asulcatus n. gen., n. sp. de l’ancien Arikarain (lointain Miocène) du Nebraska et Mioperognathus willardi n. gen., n. sp. du Barstovian (du milieu du Miocène) du Nouveau-Mexique. Eochaetodipus asulcatus n. gen., n. sp. est basé sur un crâne presque complet avec les mâchoires associées et de la matière postcrânienne. Ce spécimen est le plus ancien membre reconnu de la sous-famille Perognathinae d’après les caractéristiques du crâne et du squelette qu’il partage avec les perogna- thines actuels (infl ation mastoïde ; réduction des incisives foraminées ; séparation du buccinateur et des masticatrices foraminés ; squelette plus gracile). Eochaetodipus n. gen. est considéré comme plus primitif que d’autres perognathines parce qu’il lui manque un certain nombre de caractéristiques dérivées de ce dernier. Le crâne du Mioperognathus n. gen. fut préalablement décrit comme « Perognathus minutus ». Il MOTS CLÉS diff ère de celui d’Eochaetodipus n. gen. par certains traits qui sont considérés dérivés Mammalia, Rodentia, pour les perognathines (perte du foramen ovale accessoire ; plus grande infl ation Heteromyidae, de la bulle et du mastoïde ; réduction du squamosal à une fi ne barre ; présence Perognathinae, d’une région non ossifi ée du mur orbital ; incisives supérieures cannelées), mais trous crâniens, Barstovian, est diff érent des perognathines actuels par plusieurs caractéristiques interprétées Arikareean, comme primitives (présence de foramen temporaire ; bulle moins enfl ée ; cicatrice Miocène, genres nouveaux, temporale plus longue). Il est considéré que le groupe perognathine est issu d’un espèces nouvelles. ancêtre semblable aux Mioheteromynae, distinct des Heteromyinae.

INTRODUCTION the criteria for separating the extant taxa into sub- families could not be used; only dental characters Th e systematics of the Heteromyidae have been in were used to put the fossil taxa into the subfamilies fl ux since Wood (1935) proposed the fi rst detailed of the extant heteromyids. Wood (1935) primarily classifi cation of the family, which included all known used the morphology of the premolars to assign the extant and fossil taxa. Th e extant genera are eas- fossil taxa to subfamilies. Th is has been the standard ily divided into three subfamilies, each of which for classifi cation of the fossil heteromyids since that contains two recognized genera: Heteromyinae time (see Korth 1997: table 1, for list all of the pre- Gray, 1868 (Liomys Merriam, 1902, viously published classifi cations of heteromyids that Desmarest, 1817); Perognathinae Coues, 1875 included Tertiary taxa). Some other subfamilies have (Perognathus Wied-Neuwied, 1839, Chaetodipus been named that only included fossil heteromyids. Merriam, 1889); and Gervais, 1853 In each case, it was because more complete cranial (Dipodomys Gray, 1841, Microdipodops Merriam, material was available. Wood (1936) named the 1891; Wilson & Reeder 1993). Th ese subfamilies Florentiamyinae as a subfamily of heteromyids, but it are easily distinguishable based on drastically dif- was later recognized as a distinct family of geomyoids ferent morphologies of the skull, dentition and (Wahlert 1983). Wahlert (1991) named the subfamily postcranial skeleton (Hafner & Hafner 1983; Wil- Harrymyinae for the nominal genus based on cranial liams et al. 1993). as well as dental features, again due to the recovery Since the majority of the Tertiary fossil record of a nearly complete skull. Korth (1997) named a of heteromyids is limited to teeth and jaws, all of new subfamily, Mioheteromyinae, which included

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the majority of the fossil genera that previously had the fossil record is so incomplete, the diagnostic been included in diff erent subfamilies by diff erent morphologies of each of the genera and families authors. Th e diagnosis of the Mioheteromyinae could only be determined by direct comparison included a number of cranial features based on with more complete material. newly described cranial material. It is apparent that FOSSIL SPECIMENS. — Eochaetodipus asulatus n. gen., the diversity among heteromyids is better refl ected n. sp.: UNSM 130000, skull with associated mandibles in the features of the skull and postcranial skeleton and several postcranial bones from late Arikareean (earli- than it is in the dentition alone. est Miocene) UNSM locality Sh-112, Antelope Creek A newly discovered specimen of a heteromyid Formation, Sheridan County, Nebraska. from the late Arikareean of Nebraska includes a Mioperognathus willardi n. gen., n. sp.: FAM 129674, nearly complete cranium with incisors and right M1 nearly complete skull and jaws, and some associated (partial)-M3 from late Barstovian (middle Miocene) postcranial bones. Th is specimen and a previously Lower Pojoaque Bluff s, Pojoaque Member, Tesuque described nearly complete skull (referred to Perog- Formation, New Mexico. nathus minutus by Korth 1998) are compared to Recent heteromyids. Because of the completeness EXTANT SPECIMENS. — Liomys pictus (Th omas, 1893): AMNH 190257, 190263, 190265-190267, 190269, of these fossil specimens, it is possible to better 190276. reconstruct the phylogeny of the heteromyids, and Liomys irroratus (Gray, 1868): AMNH 172451, 172454, better defi ne the characters of the subfamilies of the 172456, 172458. Heteromyidae as they apply to fossil taxa. Liomys salvini (Th omas, 1893): AMNH 126313- 126319, 126321, 126323, 126324. Heteromys anomalis (Th ompson, 1815): AMNH 69679- ABBREVIATIONS 69686, 69688, 69689. AMNH Department of , American Museum Heteromys desnarestianus Gray, 1868: AMNH 79239, of Natural History, New York; 79241, 74542, 79244, 79246, 79248. CM Section of Mammals, Carnegie Museum of Heteromys australis Th omas, 1901: AMNH 64678, Natural History, Pittsburgh; 64680, 64681, 64689, 64690, 64696, 64863, 64866. FAM Frick Collection, American Museum of Chaetodipus hispidus Baird, 1858: CM 75174, 93588, Natural History, New York; 89207, 89208, 48912 UNSM University of Nebraska State Museum, Lin- Chaetodipus californicus Merriam, 1889: CM 71380, coln (Nebraska). 71390, 71385. Chaetodipus baileyi Merriam, 1894: CM 7517, 108271, METHODS AND MATERIALS 108272, 46366, 46367. Perognathus fasciatus Wied-Neuwied, 1839: CM 46417- 46419, 21187, 21189. TERMINOLOGY Perognathus amplus Osgood, 1900: CM 91004- Dental terminology for heteromyids follows Korth 91008. (1997: fi g. 1), and terminology for cranial foramina Perognathus parvus (Peale, 1848): CM 65351-65353, follows that of Wahlert (1974, 1985). Upper teeth 65365, 65366. are designated by capital letters, lower teeth by lower case letters. SYSTEMATIC PALEONTOLOGY

SPECIMENS EXAMINED It was necessary to compare of the fossil specimens Order RODENTIA Bowdich, 1821 with Recent species of heteromyids for several rea- Family HETEROMYIDAE Gray, 1868 sons. First, the morphologies that defi ne the dif- ferent subfamilies of the Heteromyidae are based Subfamily PEROGNATHINAE Coues, 1875 on those of the extant genera. Second, it was also necessary to determine whether the morphologies INCLUDED GENERA. — Perognathus Wied-Neuwied, 1839; of the fossil species were distinct or part of a range Chaetodipus Merriam, 1889; Oregonomys Martin, 1984; of variation within a living species. Finally, because Eochaetodipus n. gen., and Mioperognathus n. gen.

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TABLE 1. — Cranial measurements (in mm) of the holotype of skull and skeleton and the presence of a rostral Eochaetodipus asulcatus n. sp. (UNSM 13000) and Miopero- gnathus willardi n. sp. (FAM 129674). *, actual length slightly perforation anterior to the infraorbital foramen greater, anterior end of nasals missing). (diagnostic for heteromyids). It is separable from geomyids, entoptychines, and fl oreniamyids by thinner more delicate bones of the skull. It also UNSM FAM 13000 129674 lacks the cranial specializations of these groups Total length 30.2* 26.05 (see Wahlert 1983, 1985; Wahlert & Sousa 1988). Maximum rostral width 7.6 4.64 Florentiamyids also lack the lingual stylar cusps Maximum rostral depth 9.3 6.27 on the upper molars present on Eochaetodipus Length upper diastema 7.19 6.83 Minimum width, postorbital 5.9 5.15 n. gen., and have teeth that are generally more constriction robust. Greateast width of skull 13.6 11.67 Eochaetodipus n. gen. diff ers from the contem- (parietals) poraneous geomyoid Tenudomys Rensberger, 1973, Posterior width 12.2 10.39 Depth of skull at M2 10.2 7.55 again, in having a more gracile skull that is not as P4-M3 (alveolar) 5.0 3.51 deep. Th e foramina of the medial orbital wall of Tenudomys are positioned more posteriorly than in Eochaeto dipus n. gen. (Korth 1993) and the cheek Genus Eochaeotodipus n. gen. teeth of the former are generally more hypsodont and lophate (Rensberger 1973; Korth 1993). Th e TYPE SPECIES. — Eochaetodipus asulcatus n. sp. upper molars of Eochaetodipus n. gen. diff er from those of Tenudomys by having non-continuous lin- RANGE. — Late Arikareean of Nebraska (earliest Mio- cene). gual cingula. In Tenudomys, the central transverse valley of the upper molars is blocked lingually by the DIAGNOSIS. — Primitive heteromyid features: premolars lingual cingulum, whereas in Eochaetodipus n. gen. (upper and lower) simple, four-cusped, with very weak development of lophodonty; cheek teeth brachydont; upper the transverse valley is continuous and two distinct incisor asulcate; rostral perforation anterior to infraorbital fo- cusps are present along the cingulum (protostyle ramen. Primitive characters shared with mioheteromyines not and hypostyle). present in heteromyines, perogna thines and dipodomyines: Eochaetodipus n. gen. diff ers from the late Ari- no bony fl ange dorsal to orbit; large temporal foramen on kareean or early Hemingfordian Trogomys Reeder, skull; accessory foramen ovale retained (enclosed posterior border); premaxillary-maxillary suture crosses midline of pal- 1960 from southern California by its larger size, ate anterior to the posterior margin of the incisive foramina. slightly lower crowned and less lophate cheek teeth, Derived characters shared with heteromyines, perognath- and morphology of the lower premolar. In Trogo- ines, and dipodomyines, not present in mioheteromyines: mys, the cusps of the metalophid of p4 are joined length of incisive foramina less than 15% total length of anteriorly by a loph connecting their apices, giving the upper diastema; interparietal bone oval (transversely elongated); parapterygoid fossae shallower than in extant the loph an anteriorly curved shape. In Eochaeto- perogna thines, but deeper than in mioheteromyines; limb dipus n. gen., the metaconid cusps are not joined bones thinner and skull less robust. Derived features shared by a loph and will probably not fuse until a much with perognathines and dipodomyines: rudimentary infl a- later stage of wear when the bases of the cusps fuse. tion of the bulla and mastoid; masticatory and buccinator Trogomys also has a distinct supraorbital fl ange foramina separate on alisphenoid. Apomorphic features: (Reeder 1960) as in extant perognathines that is posterior palatine foramina multiple. lacking in Eochaeto dipus n. gen. ETYMOLOGY. — Greek, eos, dawn and Chaetodipus, extant Eochaetodipus n. gen. diff ers from harrymyines genus of perognathine. in lacking the specialized occlusal pattern of the cheek teeth of the latter (V-shaped hypolophid that COMPARISONS unites with the metalophid via anterior ridge on Eochaetodipus n. gen. is clearly referable to the lower cheek teeth) and the nature of the infl ation Heteromyidae because of its generally small of the auditory bullae (Wahlert 1991).

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TABLE 2. — Dental measurements (in mm) of the holotype of Eochaetodipus asulcatus n. sp. (UNSM 130000). Abbreviations: a-p, antero- posterior length; tr, maximum transverse width. Upper teeth are designated by capital letters, lower teeth by lower case letters.

P4 M1 M2 M3 I1 P4-M3 a-p tr a-p tr a-p tr a-p tr a-p tr 1.51 1.81 1.33 1.74 1.22 1.68 1.00 1.37 1.65 0.91 5.00 (left) – – 1.27 1.77 1.11 1.61 0.98 1.24 1.62 0.90 (right) p4 m1 m2 m3 i1 p4-m3 a-p tr a-p tr a-p tr a-p tr a-p tr 1.23 1.20 1.31 – 1.18 2.04 1.04 1.32 – – 4.84 (left) 1.27 1.20 1.28 1.42 1.19 1.58 1.11 1.34 1.68 0.70 4.76 (right)

Among the other subfamilies of heteromyids Eochaetodipus asulcatus n. sp. (Mioheteromyinae Korth, 1997, Perognathinae, (Figs 1-3; Tables 1; 2) Heteromyinae, Dipodomyinae), Eochaetodipus n. gen. has a mosaic of derived and primitive mor- HOLOTYPE AND ONLY SPECIMEN. — UNSM 130000, skull with associated mandibles and several postcranial phologies. Th e skull of Eochaetodipus n. gen. shares bones. the following primitive features of the skull with mioheteromyines: 1) presence of a large temporal HORIZON AND LOCALITY. — UNSM locality Sh-112, Ante- foramen; 2) position of the maxillary-premaxillary lope Creek Formation, Sheridan County, Nebraska. suture relative to the incisive foramina (crosses AGE. — Late Arikareean (earliest Miocene). fora mina anterior to posterior margin); 3) presence of an accessory foramen ovale on the alisphenoid DIAGNOSIS. — Only species of the genus. that is enclosed posteriorly; 4) lack of a bony fl ange ETYMOLOGY. — Latin, a- prefi x meaning without; and dorsal to the orbits; and 5) morphology of the sulcatus, furrow; in reference to the ungrooved upper temporalis scar on the skull (extends posteriorly incisor of this species. to occipital). Th e derived characters of Eochaetodipus n. gen. DESCRIPTION that are shared with heteromyines, perognath- Th e skull is nearly complete, lacking only the zygo- ines and dipodomyines include shorter incisive matic arches and the anterior end of the rostrum foramina (less than 15% the length of the di- (Fig. 1). Some damage has removed most of the bone astema), deeper parapterygoid fossa (not as deep from the orbital wall. Th e skull is similar in overall as in extant heteromyids, but deeper than in proportions and size to the extant perognathine spe- mioheteromyines); and more gracile limb bones. cies Chaetodipus hispidus Baird, 1858, but lacks the Eochaetodipus n. gen. also shares some derived degree of infl ation of the mastoids present in the characters of the skull with perognathines (infl a- latter. In dorsal view, the snout broadens anteriorly tion of bulla and mastoid). Th e arrangement of rather than tapering as in Chaetodipus Merriam, the foramina on the lateral alisphenoid in Eocha- 1889. Th is may be aff ected by the breakage and etodipus n. gen. is unique among heteromyids. In dorsoventral crushing of the anterior part of the Eochaetodipus n. gen. the accessory foramen ovale rostrum. Th e nasal bones end posteriorly anterior is large, and completely surrounded by bone, to the anterior margin of the orbits. Th e premaxil- and the buccinator and masticatory foramina laries extend slightly farther posteriorly, level with are separate from one another. Th is condition is the anterior margin of the orbits. Th ere is no fl ange known only elsewhere within the geomyoids in on the frontals dorsal to the orbits, which is a char- the entoptychines, a group clearly not closely al- acteristic of extant heteromyids (Wahlert 1985). Th e lied with Eochaetodipus n. gen. crest formed by the temporalis is similar to that of

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A

tfreth

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foa rp msc spv bu mbf vf in C

ppl pom fo

FIG. 1. — Photographs (left) and line diagrams (right) of the skull of Eochaetodipus asulcatus n. sp. based on the holotype UNSM 130000: A, dorsal view; B, lateral view (zygomatic arch removed); C, ventral view. Dashed lines indicate outlines of broken or covered areas; patterned area indicates missing bones. Abbreviations: bu, buccinator foramen; eth, ethmoid foramen; fo, foramen ovale; foa, accessory foramen ovale; fr, nutritive foramen in frontal; in, incisive foramen; mbf, fi ssure medial to bulla; msc, masticatory fora- men; spv, sphenofrontal vacuity; pom, posterior maxillary foramen; ppl, posterior palatine foramen; t, temporal foramen; rp, rostral perforation (including infraorbital foramen); vf, venous foramen. Scale bar: 1 cm. extant Heteromys Desmarest, 1817 (Wahlert 1985: diameter) is present along the squamosal-temporal fi g. 2), mioheteromyines (Korth 1997: fi g. 8), and suture, level with the base of the zygomatic root. Harrymys Munthe, 1988, originating above the Th e mastoids are slightly swollen, not as much as orbits and extending posterodorsally to the nuchal in extant perognathines, but are infl ated enough crest (Wahlert 1991: fi g. 1). Th e two ridges mark- to project posteriorly, producing low, broad ridges ing the attachment of the temporalis do not meet, along the lateral sides of the occiput. Although there and are separated by the width of the interparietal is breakage on the mastoids, matrix has fi lled the (6.35 mm). Th e interparietal is oval in shape and broken areas, and it is not possible to determine wider than the postorbital constriction, a condition if there is any cancellous bone present as in extant in extant Chaetodipus and other heteromyids, that perognathines. diff ers from extant Perognathus Wied-Neuwied, Damage to the rostrum has obliterated the pattern 1839 and dipodomyines where the interparietal of the premaxillary-maxillary suture on the lateral is greatly reduced in size to accommodate bullar sides. Along the ventral margin of the rostrum, the infl ation. A large temporal foramen (0.75 mm in premaxillary-maxillary suture appears anterior to

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the rostral perforation and extends posteriorly along A the ventral boundary of the infraorbital foramen before crossing the palatal surface. Th e infraorbital foramen is large with an associated rostral perforation (typical of heteromyids) that is situated low on the rostrum, near the ventral border. A small swelling of bone is ventral to the infraorbital foramen. As stated above, little of the morphology of the orbital wall is preserved, but there are three recognizable foramina preserved on the right side of the skull. A small, crescentic ethmoid foramen is present dorsal to M2, just above the center of the orbital wall. A B small frontal foramen is also present along the dorsal border of the orbit, well posterior to the tooth row. Th e opening for the sphenopalatine vacuity is just dorsal to the tooth row and just posterior to M3. Although there is damage to the orbital wall, the contact between the orbitosphenoid and frontal is present on one side of the skull. In species of perognathines and dipodomyines there is an un- C ossifi ed area (Wahlert 1985; Korth 1998). Th is unossifi ed area is clearly not present on UNSM 130000. Th e alisphenoid extends dorsally only as high as the glenoid fossa. Th ere is no distinct muscle attachment on the dorsal alisphenoid as in geomyids, but ventral to the anterior margin of the zygomatic root on the squamosal is a bony FIG. 2. — Mandible and cheek teeth of Eochaetodipus asulcatus n. sp. (UNSM 130000): A, lateral view of mandible; B, right p4- knob. Th is knob of bone is slightly enlarged by m3 (anterior to right); C, left P4-M3 (anterior to left). Scale bars: distortion of the skull, but is similar to a recurved A, 5 mm; B, C, 1 mm. ridge present in perognathines along the anterior margin of the glenoid fossa. On the posterolateral portion of the alisphenoid are three foramina. Th e heteromyines (Korth 1997). Th e palatal surface accessory foramen ovale is the largest (0.5 mm), is smooth and slightly concave ventrally with no most ventral, and most posterior. It is circular in grooves or ridges. Th e maxillary-palatine suture shape. Th e other two foramina are the mastica- extends anteriorly on the palate to the level of the tory and buccinator. Th e masticatory foramen is posterior margin of P4. Th ere are three pairs of dorsal and slightly posterior to the buccinator. It is posterior palatine foramina medial to the molars. crescentic in shape and opens anterodorsally. Th e Th e posterior maxillary foramen is an elongated oval buccinator is a small, nearly horizontal slit, just along the maxillary-palatine suture posteromedial posterior to the tooth row. to M3. Th e parapterygoid fossa is shallower than in Th e incisive foramen is small and tear-drop shaped. Chaetodipus but deeper than in mioheteromyines Its length (1.0 mm) is approximately 14% that of with a large opening for the sphenofrontal canal the total length of the upper diastema, well within in the center of the anterior margin of the fossa. the range of extant heteromyids (Wahlert 1985). Posterior and slightly lateral is the foramen ovale, Th e premaxillary-maxillary suture crosses the mid- along the posterolateral margin of the fossa. line of the palate just anterior to the posterior end None of the auditory bullae is fully preserved, of the incisive foramen as in Harrymys and mio- but an anteroventral portion is preserved on both

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sides. Where exposed, the bullar wall is a single Th e cheek teeth are brachydont as in species of lamina of bone. Th e bullae are slightly infl ated and perognathines. P4 is only preserved on the left end anteroventrally in a point (directed antero- side. It has a simple geomyoid pattern of four cusps medially), but do not reach the center-line of the (Fig. 2A). Th e protocone is the only cusp on the skull. Th ere is a small, slit-like opening along the protoloph and is round in occlusal outline. Th ere is medial border of the bulla that appears to be the a minute swelling on the buccal slope of the proto- same as that identifi ed by Wahlert (1985: fi g. 2) as cone (?paracone). Th e protocone is isolated, not the “fi ssure medial to bulla” in extant Heteromys. No connected to any of the cusps of the metaloph. Th e other foramina are recognizable in the basicranial three cusps of the metaloph (hypostyle, hypocone, area due to breakage. and metacone) are separated from one another by No cranial foramina are recognizable on the narrow valleys. Th e valley separating the hypocone back of the skull except the foramen magnum, and metacone is shallower, suggesting that the two again due to breakage. Th e nuchal crest is very cusps will fuse after moderate wear. Th e cusps of low (not extending dorsal to the parietal bones) the metaloph form a curved loph that is concave and has a small V at its center at the highest point anteriorly in occlusal outline. on the skull. A low, rounded ridge runs ventrally M1 and M2 are nearly identical, M2 being slightly from the apex of the occipital toward the foramen shorter (anteroposteriorly). Th ese molars are the magnum. Laterally, the two ridges formed by the typical six-cusped, bilophate molars of heteromyids. infl ated mastoids are approximately as distinct as Th e central cusps (protocone, hypocone) are the the central ridge of the occipital. largest and the lingual styles (protostyle, hypostyle) Th e mandible is slender, typical for heteromyids are the smallest cusps. Th ere is a narrow valley (depth below m1 = 4.1 mm and 4.0 mm: Fig. 2C). separating the styles, and a deeper valley that con- Th e diastema is nearly as long as the tooth row tinues buccally, separating the rest of the protoloph (4.1 mm) and shallow. Th e mental foramen is just and metaloph cusps. Th e anterior cingulum on above mid-depth of the mandible and just behind M1 and M2 originates at the protostyle and runs the center of the diastema. Th e masseteric fossa is buccally, anterior to the protocone, ending at the shallow with only a ventral ridge. Th e ventral ridge anterolingual corner of the paracone. Th e valley runs anteriorly from the angle along the ventral between the anterior cingulum and protoloph is border of the mandible, then angles anterodorsally narrow (narrower on M2) and will probably fuse from a point below p4 and ends at the posteroven- with the protoloph after moderate wear. tral border of the mental foramen. M3 is the smallest molar and oval in occlusal Th e ascending ramus originates lateral to m2 outline. Th e protoloph is the same as in the ante- and blocks m3 from lateral view. Th e angle of the rior molars with three recognizable cusps. However, mandible has a sharp point posteriorly, similar the posterior half of the tooth is reduced. Th ere to Chaetodipus, but does not fl are laterally as in is no hypostyle present. A lingual cingulum runs the former, it is in the same plane as the condyle. posteriorly from the protostyle, then fuses with the Anterior to the condyle is a rounded swelling for hypocone posteriorly. Th ere is no valley along the the base of the incisor. Th e coronoid process is not lingual border of the tooth as in the anterior molars. preserved on either of the mandibles, but the base Th e metacone is reduced to a minute swelling at of the process is recognizable, and very small, sug- the buccal end of the metaloph. gesting a minute process. Th ere is no indication as Th e proportions of the lower incisor are similar to to whether it was laterally defl ected. those of the upper incisor, but the anterior enamel Th e upper incisors are separated from the skull, but surface is more strongly convex with no indica- both are present. In cross-section, they are longer (an- tion of fl attening. Th e lower premolar is simple. It teroposteriorly) than wide with a gently convex (nearly consists of four rounded, subequal cusps, with no fl at) anterior enamel surface that extends about one- indication of the development of lophodonty. Th e fourth the height of the tooth on the lateral side. cusps of the metalophid (metaconid, protostylid)

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C E

D

FIG. 3. — Postcranial elements and mandible of Eochaetodipus asulcatus n. sp. (UNSM 130000): A, ulna (distal end missing); B, tibiofi bula (proximal end and fi bula broken); C, humerus (proximal end missing); D, calcanium; E, lateral view of right mandible. Scale bar: 5 mm. are closer together than the cusps of the hypolophid metaconid. Th e cusps of the hypolophid join by (hypoconid, entoconid). Th is makes the tooth nar- fusing at their anterior margins. rower anteriorly than posteriorly (Fig. 2B). Th ere is Th e last lower molar is smaller than the anterior no indication that the anterior and posterior pairs molars, but with basically the same occlusal pattern. of cusps will unite at the center of the tooth as in Th e hypolophid is slightly reduced by the reduction Perognathus and Chaetodipus. Instead, it appears in the hypostylid and entoconid (similar to M3). that each of the cusps of the metalophid will unite Among the postcranial fragments associated with the hypolophid independently. Th e only other with UNSM 130000 are: humerus lacking proxi- cuspule present on p4 is a minute hypoconulid mal end; two tibia-fi bulas lacking both ends; two between the hypolophid cusps along the posterior calcanea (one broken); several vertebral fragments border of the tooth. and phalanges (Fig. 3). Comparison of these bones Th e fi rst and second lower molars, as with their with those of an equivalent-sized specimen of Cha- upper counterparts, are bilophate and six-cusped. etodipus hispidus shows very little diff erence in size Th e buccal stylids (protostylid, hypostylid) are the and proportions. Korth (1997) stated that the smallest cusps; the remainder are subequal in size. limb bones of mioheteromyines were slightly more A deep valley runs transversely across the occlusal robust than those of extant heteromyids, but the surface of the teeth separating the metalophid and bones associated with UNSM 130000 are equally hypolophid cusps. Th e only cingulum present is one proportioned with those of Chaetodipus. that originates buccally at the anterior margin of the protostylid and wraps around the anterobuccal DISCUSSION corner of the tooth, ending at the center of the an- Eochaetodipus n. gen. has several primitive characters terior margin of the tooth. Both the metaconid and that are shared with the mioheteromyines and extant protoconid extend small arms to unite anteriorly with heteromyines. Th e general shape of the mandible of the cingulum. Th e arm is directed anterolingually Eochaetodipus n. gen. is similar to that of miohetero- from the protoconid and anterobuccally from the myines and heteromyines with a deep emargination

GEODIVERSITAS • 2008 • 30 (3) 601 Korth W. W.

between the angle and the condyle, but the angle is of mioheteromyines and similar to those of extant not strongly defl ected laterally as in perognathines perogna thines and heteromyines. and dipodomyines. On the cranium, the muscle scar Th e cheek teeth of Eochaetodipus n. gen. are for the temporalis in Eochaetodipus n. gen. extends brachydont and have a primitive heteromyid oc- the full length of the parietals as in mioheteromyines clusal morphology. Th is bars Eochaetodipus n. gen. and extant heteromyines. In perognathines and dipo- from inclusion in the Dipodomyinae, which are domyines, this scar is greatly shortened posteriorly, distinguished by much higher crowned cheek teeth mainly due to the infl ation of the bullae. Th e bulla in (at least mesodont). perognathines and dipodomyines is greatly infl ated. Wood (1935) separated fossil species into the Th e primitive condition in extant heteromyines and Heteromyinae and Perognathinae, based on the mioheteromyines, is a small bulla with little or no union of the lophs of p4. In fossil perognathines, infl ation. Th e bulla and mastoid in Eochaetodipus the union was central and in heteromyines, the un- n. gen. is intermediate. It is only slightly enlarged ion was either buccal or lingual of the center of the and shows the beginnings of the infl ation of the tooth, leaving a central basin. However, this distinc- mastoid present in perognathines. tion appears to break down in the more primitive Eochaetodipus n. gen. has some derived features species. In early heteromyids like Proheteromys and that appear to ally it with the perognathines and Mookomys Wood 1931, the cheek teeth are fairly dipodo myines, but not the heteromyines. Th e primi- low-crowned and the cusps of the metalophid of p4 tive condition in geomyoids is that the buccinator do not form a distinct loph, but rather are isolated and masticatory foramina are fused; this is the case and circular in occlusal outline. Th e union of either in heteromyines and mioheteromyines (Korth 1997: of these metalophid cusps to the hypolophid is usu- fi g. 11). In perognathines and dipodomyines, the ally at the greatest anteroposterior diameter of the two foramina are separated. Th e latter condition cusp (even with the center), so the ultimate union is present in Eochaetodipus n. gen. However, the with the hypolophid is never central, but neither is primitive condition of the accessory foramen ovale it distinctly buccally or lingually placed to form a is a large, round foramen on the posteroventral central basin. Th is suggests that the central union of corner of the alisphenoid (Korth 1997). In the de- the lophs in the premolar of extant perognathines rived condition, the accessory foramen ovale is lost is a derived condition, but so is the development completely (perognathines and dipodomyines), or of a central basin due to the buccal and lingual fu- at least the posterior border is lost (heteromyines). sion of the lophs of the premolars in extant hetero- Th e condition in mioheteromyines and harrymyines myines. Th e premolars of Eochaetodipus n. gen. are is a complete accessory foramen ovale and fused brachydont and the cusps are simple and rounded, buccinator and masticatory foramina, believed as would be expected in the primitive condition for to be the primitive condition for heteromyids. In heteromyids. Th e fusion of the lophs of the lower Eochaetodipus n. gen., the entire accessory foramen premolar lacks the derived condition of either the ovale is retained as in mioheteromyines and harry- perognathines or heteromyines. Similarly, the lower myines (primitive) but the buccinator and masti- premolars of several of the genera included in the catory foramina are no longer fused similar to the Mioheteromyinae are not necessarily derived in the perognathines and dipodomyines (derived). Th e direction of extant heteromyines, but refl ect their condition in Eochaetodipus n. gen. appears to be primitive nature (see Korth 1997 for fi gures). transitional between the mioheteromyine condition It has also been the practice of authors to include and that of perognathines and dipodomyines but fossil taxa with low-crowned cheek teeth in the Pero- not with heteromyines. gnathinae because that is the condition in extant Korth (1997) noted that the postcranial bones Perognathus and Chaetodipus. However, it is just as of mioheteromyines were more robust than those likely that these fossil taxa are simply earlier, primi- of extant heteromyids. Th e postcranial bones of tive members of other subfamilies that have not yet Eochaetodipus n. gen. are more gracile than those modifi ed their dentition towards hypsodonty. It is

602 GEODIVERSITAS • 2008 • 30 (3) New Miocene Heteromyidae (Mammalia, Rodentia)

easy to exclude fossil species from the Perognathinae margin of the tooth (Sutton & Korth 1995). In by the presence of mesodont or hypsodont cheek the holotype of Eochaetodipus asulcatus n. sp., the teeth, but inclusion for the primitive morphology anterior cingulum of M2 is nearly as complete (brachydonty) is not justifi ed. as in M1, running nearly the entire width of the It appears that Eochaetodipus n. gen. represents tooth anteriorly, joining the protostyle lingually. a primitive perognathine based on skeletal and Th e only other species noted with this morphology dental features, diff ering only from extant genera was the specimens referred to “P. minutus” from the of the subfamily by the retention of several primi- Barstow Formation (Lindsay 1972: fi g. 22c) and tive heteromyid characters. P. ancenensis from Montana (Sutton & Korth 1995: Th ree Tertiary species previously referred to Pero- fi g. 9A, B). Th is feature was used to diagnose the gnathus may be referable to Eochaetodipus n. gen.: latter species. Unfortunately, M2 is unknown for Perogna thus trojectioansrum Korth, 1979 from the P. trojectioansrum (Korth, 1979). late Barstovian of Nebraska, P. ancenensis Sutton & Th e fi nal distinctive feature of these species is the Korth, 1995 from the early Barstovian of Montana, masseteric scar on the mandible. In all heteromyids, and specimens referred to P. minutus, James, 1963 the anterior extent of the masseteric scar is a small from the Barstovian of southern California (Lindsay shelf on the lateral side of the mandible that extends 1972). Th ere are several features that these species anterior to p4. In all Tertiary and Recent specimens share with Eochaetodipus n. gen. that are distinct of Perognathus and Chaetodipus, the anterior end from all other Tertiary and Recent species of Pero- of this shelf is dorsal to the mental foramen and g nathus (including Recent Chaetodipus). extends anteriorly to at least the anterior margin of Th e fi rst morphology is the occlusal pattern of the foramen. On the mandible of E. asulcatus n. sp. p4. On the holotype of P. minutus, UCMP 54575 this scar ends posterior to the mental foramen. Th is from the Clarendonian (James 1963: fi g. 45), the same condition is true for P. trojectioansrum (Korth anterior cusps (metaconid and protostylid) unite 1979: fi g. 3C). Th e mandible of P. ancenensis and posteriorly and form a short loph that runs poste- the referred Barstovian specimens of “P. minutus” riorly and joins the center of the hypolophid. Th is from Barstow are not known. loph is not present on the stratigraphically lower Th e similarities of these three species (“P. ” ancen- referred specimens of P. minutus from the Barstovian ensis, “P. ” trojectioansrum, and “P. minutus”) to of California (Lindsay 1972: fi g. 22i). It is also lack- E. asulcatus n. sp. suggest that they may be referable ing on the referred specimens of P. trojectioansrum to Eochaetodipus n. gen. However, all of these shared (Korth 1979: fi g. 3B) and P. ancenensis (Sutton & features appear to be primitive, so their presence in Korth 1995: fi g. 9C, D) which is the same morpho- these species may exclude them from Perognathus logy of the p4 of E. asulcatus n. sp. (Fig. 2B). Th is or Chaetodipus, but it does not automatically in- character does not appear to be variable. All Recent clude them in Eochaetodipus n. gen. Since all the specimens of Chaetodipus and Perognathus examined characters are not known for all of the species, it have this feature. In all other described Tertiary is impossible to include them in Eochaetodipus n. species of Perognathus, the loph connecting the gen. at this time. anterior cusps of p4 to the hypolophid is present. It appears likely that the specimens identifi ed by Lindsay (1972) as P. minutus are referable to a dif- Genus Mioperognathus n. gen. ferent species based on this character. Another feature that unites these species to Eochae- TYPE SPECIES. — Mioperognathus willardi n. sp. todipus n. gen. is the morphology of the anterior RANGE. — Middle Barstovian (middle Miocene) of cingulum of M2. On all other fi gured Tertiary New Mexico. species of Perognathus, the anterior cingulum is DIAGNOSIS. — Derived perognathine features shared with either absent or reduced to a minute cusp between Perognathus and Chaetodipus: mastoid and auditory bulla the paracone and protocone along the anterior infl ated; upper incisor grooved; accessory foramen ovale

GEODIVERSITAS • 2008 • 30 (3) 603 Korth W. W.

absent; unossifi ed area present on medial orbital wall; of Mioperognathus n. gen. is believed to be more premaxillary-maxillary suture crosses palate at posterior primitive because these features are similar to those end of incisive foramina; buccinator and masticatory foramina separate; optic foramen greater than 1 mm in of mioheteromyines and other geomyoids. diameter. Primitive perognathine features: cheek teeth brachydont and bilophate; stapedial foramen present in bulla. Retained primitive heteromyid features lost in Mioperognathus willardi n. sp. Perognathus and Chaetodipus: length of incisive foramina (Fig. 4; Table 1) more than 15% of that of upper diastema; temporal foramen present on skull; scar for temporalis muscle Perognathus minutus – Korth, 1998 (in part). extends onto parietal bones; mastoid and bulla infl ated, but less than in Chaetodipus; no bony fl ange above orbits. HOLOTYPE. — FAM 129674, nearly complete cranium Autapomorphic features: molars greatly decrease in size with incisors and right M1 (partial)-M3. from M1 to M3; M3 markedly smaller than M2 and circular in occlusal outline. OCCURRENCE. — Lower Pojoaque Bluff s, Pojoaque Member, Tesuque Formation, New Mexico. ETYMOLOGY. — Th e name is intended to refl ect the age of occurrence (Miocene) and the close systematic AGE. — Late Barstovian (middle Miocene). relationship to Perognathus. DIAGNOSIS. — Only species of the genus.

DISCUSSION ETYMOLOGY. — Patronym for Willard Korth for his Mioperognathus n. gen. is clearly referable to the physical and moral support of my research. Perognathinae based on the cranial characters used DENTAL MEASUREMENTS. — M1, tr = 1.00 mm; M2, by Wahlert (1985: 14) to distinguish the three ex- a-p = 0.69 mm, tr = 0.89 mm; M3, a-p = 0.43 mm, tant subfamilies of the Heteromyidae (large optic tr = 0.55 mm (from Korth 1998: table 1). Abbrevia- foramen, non-ossifi cation on orbital wall including tions as in Table 2. ethmoid foramen, infl ated auditory bullae with anteroventral processes approaching each other DESCRIPTION and touching basisphenoid, squamosal bone ex- Th e cranium and upper molars of Mioperognathus tending as thin process posteriorly above acoustic n. gen., FAM 129674, have been previously de- meatus, upper incisors grooved). In addition, the scribed in detail as those of Perognathus minutus brachydont cheek teeth of Mioperognathus n. gen. (Korth 1998: 133). Since there is no additional are similar to that of perognathines, and do not at- material available, nothing will be added to the tain the mesodonty or hypsodonty of hetermyines original description. or dipodomyines. Mioperognathus n. gen. diff ers from Perognathus DISCUSSION and Chaeto dipus in lacking a number of derived Korth (1998) originally referred FAM 129674 to character states (shorter incisive foramina; loss of Perognathus minutus James, 1963 because of its temporal foramen; scar for temporalis limited to similar size and time equivalent occurrence to the frontal bone; marked mastoid and bulla infl ation; species from southern California (Lindsay 1972). bony fl ange above orbits). In Mioperognathus n. gen., However, based on dental measurements, the de- these character states are expressed as: a large, dis- scribed specimen is distinctly smaller than the tinct temporal foramen; the length of the incisive Barstovian sample of “P. minutus” from California foramen is over 20% that of the upper diastema; the (Lindsay 1972: table 9; Korth 1998: table 1). Th e scar for the temporalis muscle extends posteriorly only described Tertiary species of Perognathus that for nearly the entire length of the parietal bones; is similar in size is “P. ” trojectioansrum from the there is some bullar and mastoid infl ation, but much Barstovian of the northern Great Plains. less than in Chaetodipus (the extant perognathine In addition to overall size, there is another fea- with the least amount of infl ation of this area); and ture that separates FAM 129674 from specimens there is no fl ange of bone above the orbits. Th e skull of P. minutus; the relative sizes of the upper molars

604 GEODIVERSITAS • 2008 • 30 (3) New Miocene Heteromyidae (Mammalia, Rodentia)

A

B sty fo vf in ju ppl

fm

spt pom st mbf uaf t uml C

bu spl rp msc op spv

D

FIG. 4. — Cranium and upper molars of Mioperognathus willari n. sp. (FAM 129674) (holotype): A-C, photographs (left) and line diagrams of the cranium; A, dorsal view; B, ventral view; C, right lateral view (zygomatic arch removed); D, right M1(broken)-M3 (stereo pair; anterior toward top). Abbreviations: bu, buccinator foramen; fm, foramen magnum; fo, foramen ovale; in, incisive foramen; ju, jugular foramen; mbf, fi ssure medial to bulla; msc, masticatory foramen; op, optic foramen; pom, posterior maxillary foramen; ppl, posterior palatine foramen; spl, sphenopalatine foramen; spt, spheopterygoid canal; spv, sphenofrontal vacuity; rp, rostral perforation (including infraorbital foramen); st, stapedial foramen; sty, stylomastoid foramen; t, temporal foramen; uaf, unossifi ed area between alisphenoid and frontal bones; uml, unossifi ed area between maxillary and lacrimal bones; vf, venous foramen. Scale bars: A-C, 1 cm, D, 1 mm.

GEODIVERSITAS • 2008 • 30 (3) 605 Korth W. W.

TABLE 3. — List of character states used in PAUP analysis.

1. Bony fl ange above orbit: absent (0), present (1). 2. Length of incisive foramen compared to total length of upper diastema: >23% (0), between 23 and 15% (1), <15% (2). 3. Infl ation of auditory bulla and mastoid: absent (0), present (1). 4. Unossifi ed area on orbital wall: absent (0), present (1). 5. More gracile limb bones: absent (0), present (1). 6. Size of optic foramen: <1mm in diameter (0), >1mm in diameter (1). 7. Groove on upper incisor: absent (0), present (1). 8. Stapedial foramen (artery): present (0), absent (1). 9. Loph of p4 united by central loph: absent (0), present (1). 10. Central basin formed on p4: absent (0), present (1). 11. Where premaxillary-maxillary suture crosses the midline of the palate: anterior to the posterior margin of the incisive foramen (0), at the posterior end of the incisive foramen (1). 12. Crown-height of cheek teeth: brachydont (0), mesodont (1). 13. Buccinator and mastecatory foramina: fused (0), separate (1). 14. Accessory foramen ovale on alisphenoid: present and complete (0), present but lacking posterior margin (1), absent (2). 15. Temporal foramen: present (0), absent (1). 16. Length of scar for temporalis muscle: complete to occipital (0), shortened (1). 17. Shape of interparietal bone: triangular (0), oval (1). 18. Depth of parapterygoid fossa: shallow (0), deeper (1), extremely deep (2). 19. Angle of the mandible: straight (0), defl ected (1). 20. Bone of the bulla: single lamina (0), trabeculate (1). 21. Squamosal reduced to thin bar posteriorly: absent (0), present (1).

TABLE 4. — Character matrix of taxa used in PAUP analysis.

12 3 456 7 8 9 101112131415161718192021 Mioheteromyinae 0 0 0/1 0 0 0 0/1 0 0 0 0 0/1 00000000 0 Heteromys/Liomys 1200100 1010 1 01100200 0 Eochaetodipus 021?1?0 0000 0 10001100 0 Mioperognathus 0111?11 0001 0 12001100 0 Perognathus/ 1211111 0101 0 12111211 1 Chaetodipus

(Fig. 4D). In all described species of Perognathus, is similar in size, but it diff ers from M. willardi M1 and M2 are nearly identical in size, M2 be- n. sp. in lacking the diff erence in proportional size ing approximately 95% the width of M1. On the of the upper molars. Although no M2s or M3s of holotype of M. willardi n. sp., M2 is less than “P.” trojectioansrum were reported, measurements 90% the size of M1. Even more strikingly, M3 on taken from the fi gured maxilla with alveoli for these FAM 129674 is markedly smaller than M2 having teeth (UNSM 56313; Korth 1979: fi g. 3A) dem- a transverse width of only 62% that of M2 (Korth onstrate that the width of M2 is 98% that of M1, 1998: table 1). On all species of Perognathus, M3 M3 has 80% the width of M2, and M3 is wider is usually smaller than M2 but has over 80% the than long (oval in occlusal outline). transverse width of M2. Besides its smaller size, Mioperognathus n. gen. diff ers from Eochaetodipus M3 of M. willardi n. sp. is circular in occlusal n. gen. in several features of the skull that are shared outline, not oval as in species of Perognathus and with extant Perognathus: 1) loss of the accessory other perognathines. “Perognathus” trojectioansrum foramen ovale; 2) greater infl ation of the bulla and

606 GEODIVERSITAS • 2008 • 30 (3) New Miocene Heteromyidae (Mammalia, Rodentia)

ABMioheteromyinae

Mioheteromyinae

Heteromyinae Eochaetodipus 3

Eochaetodipus 1 Mioperognathus Mioperognathus 2 4 Perognathus Perognathus- 5 Chaetodipus 6 Dipodomyinae 7 Heteromys

FIG. 5. — Phylogenies of selected heteromyid taxa: A, Cladogram of relationships of heteromyids. Explanation of nodes: 1, Hetero- myidae; buccinator and masticatory foramen (fused) separated from accessory foramen ovale; rostral perforation associated with infraorbital foramen. 2, More gracile skeleton; incisive foramen less than 15% length of upper diastema. 3, Heteromyinae; bony fl ange above orbit; loss of stapedial foramen; mesodonty; central basin on lower premolar; deeper parapterygoid fossa; loss of posterior border of accessory foramen ovale. 4, beginnings of bullar and mastoid infl ation; buccinator and masticatory foramina separated; interparietal oval. 5, presence of unossifi ed area on medial orbital wall; loss of accessory foramen ovale; premaxillary-maxillary suture on palate crosses incisive foramina at their posterior end; greater infl ation of bulla and mastoid. 6, central union of lophs on p4; deeper parapterygoid fossa; loss of temporal foramen; bony fl ange above orbit; even greater infl ation of mastoid and bulla. 7, Dipodomyinae; bulla enormously infl ated; limb proportions for ricochetal locomotion; incisive foramina greatly enlarged; cheek teeth mesodont to hypsodont. B, Single most parsimonious tree based on PAUP analysis. Total length = 27 steps. Consistency index = 0.8889. Homo- plasy index = 0.1111. Retention index = 0.7500. Multiple derived states for characters 2, 14, and 18 are ordered. See Table 3 for list of character states. mastoid; 3) shorter posterior extent of the temporalis DISCUSSION muscle scar; 4) presence of an unossifi ed area on the orbital wall; 5) squamosal reduced to a thin bar of Eochaetodipus n. gen. is referred to the Pero gnathinae bone posteriorly; and 6) sulcate upper incisors. Th e based on several derived characters of the skull infl ation of the mastoid, extent of the temporalis and skeleton shared with extant perognathines. muscle scar, and width of the interparietal bone Eochaeto dipus n. gen. has a reduced incisive fo- in Mioperognathus n. gen., are not as derived as in ramen (length less than 15% that of upper di- Recent Perognathus or Chaetodipus. Mioperognathus astema). In mioheteromyines and harrymyines, n. gen. also retains the temporal foramen as in the ratio of the length of the incisive foramen to Eochaetodipus n. gen. In one cranial feature, the the total length of the upper diastema ranges from earlier and generally more primitive Eochaetodipus 24 to 46% (Korth 1997: table 5). Primitively, in n. gen. is more derived (closer to the morphology mioheteromyines and harrymyines, the buccinator of Perognathus) than Miopero gnathus n. gen. Th e and masticatory foramina are fused into a single relative length of the incisive foramina compared foramen. In Eochae todipus n. gen., these foramina to the length of the upper diastema in the latter are separated as in extant perognathines. Th e inter- is approximately 23%, whereas in Eochaetodipus parietal in harrymyines and mioheteromyines is n. gen. and extant perognathines, it is less than 15%. triangular in shape, similar to extant heteromyines. Mioperognathus willardi n. sp. is also much smaller In Eochaetodipus n. gen., the interparietal is oval in in size than E. asulcatus n. sp. Eochaetodipus n. gen. shape and very broad. Th is same broad, oval shape also lacks the marked reduction in size of the upper is also present in Perognathus and Chaetodipus. Th e molars present in Mioperognathus n. gen. bulla and mastoid of Eochaeto dipus n. gen. show

GEODIVERSITAS • 2008 • 30 (3) 607 Korth W. W.

the beginnings of infl ation but it is not as marked these same relationships. Mioperognathus n. gen. is as in extant perognathines, but is clearly greater also temporally intermediate between Eochaetodipus than that in heteromyines. One mioheteromyine n. gen. and perognathines. shows similar infl ation of the mastoid and bulla, Th e morphocline for many cranial and dental Schizodontomys Rensberger 1973 (Korth et al. 1990). characters in perognathines goes from Eochaetodipus Th e harrymyine genus Harrymys also has an infl ated n. gen., to Mioperognathus n. gen., to Chaetodipus, bulla and mastoid (Wahlert 1991). It is suggested and fi nally to Perognathus. Th is sequence is also here that the bullar infl ation occurred separately refl ected in the fossil occurrence of these genera: in Schizodon tomys and Harrymys because of the Eochaetodipus n. gen. is late Arikareean; Mioperog- distinctive nature of their cheek teeth (increased nathus n. gen. is Barstovian; and all fossil species crown height, occlusal pattern) and lack of any of previously referred to Perognathus are Barstovian the other derived cranial characters of perognathines. and younger. Because other mioheteromyines, such as Balantiomys, Extant heteromyines have been generally grouped lack this infl ation (Gazin 1932; Wood 1935; Korth with the perognathines because of several derived char- 1997), it is not likely a primitive condition for that acters: fl ange above the orbit; reduced size of incisive subfamily or for the entire Heteromyidae. foramen; loss of the temporal foramen; more gracile Th e fi nal feature of Eochaetodipus n. gen. that is limb bones; deeper parapterygoid fossa; and loss of shared with extant perognathines is the slender- the accessory foramen ovale. With the recognition of ness of the limb bones. Th e bones of Eochaetodipus Eochaetodipus n. gen. and Mioperognathus n. gen., it n. gen. are more delicate than any known for a appears that several of these features were arrived at mioheteromyine. independently from the perognathines. Extant hetero- Eochaetodipus n. gen. cannot be referred to ei- myines retain an uninfl ated bulla and mastoid, and ther of the extant genera of perognathines because fusion of the buccinator and masticatory foramina. it lacks a number of derived features: 1) grooved Both these features are derived in both Eochaetodipus upper incisor; 2) loss of temporal foramen; 3) loss n. gen. and Mioperognathus n. gen., and shared with of accessory foramen ovale; 4) unossifi ed area on perognathines. Th e loss of the accessory foramen orbital wall; 5) reduced (shortened) temporalis ridge; ovale in heteromyines is also present in Miopero- 6) greater infl ation of mastoid and bulla; 7) angle of gnathus n. gen., suggesting a separate development mandible defl ected laterally; and 8) central union of of this feature. Th e only feature not present in either lophs on p4. Th e character state of all these features Eochaetodipus n. gen. or Mioperognathus n. gen. is the in Eochaetodipus n. gen. is primitive, and similar to bony fl ange above the orbits. Extant heteromyines that of mioheteromyines and harrymyines. also have lost the stapedial foramen, a derived feature Th e cranium of Mioperognathus n. gen. is markedly not present in any other heteromyids, extant or fossil similar to the skulls of modern perognathines but (unknown in Eochaetodipus n. gen.). retains a large temporal foramen, has less infl ation of Th e Perognathinae could have easily arisen from the mastoids, and has the primitive condition of the a primitive mioheteromyine ancestor during the temporalis muscle scar (continuous for full length of Arikareean. Th e earliest perognathine is Eochaeto- parietals). However, this skull has several features of dipus n. gen., which shares a number of the primitive extant perognathines that are lacking in Eochaetodipus cranial and dental features of the mioheteromyines. n. gen.: 1) greater infl ation of mastoid; 2) grooved Extant heteromyines represent a diff erent clade that upper incisor; 3) loss of accessory foramen ovale; and likely arose from a mioheteromyine ancestor as well, 4) unossifi ed area on orbital wall. Miopero gnathus but separately from the perognathines. n. gen. is clearly intermediate in morphology be- tween Eochaetodipus n. gen. and extant perognathines (Fig. 5A). PAUP analysis was run on the cranial and Acknowledgements dental features of the perognathines discussed (Ta- Th e UNSM specimen was collected by B. E. Bailey and bles 3, 4). Th e resulting phylogeny (Fig. 5B) shows fi eld crew as part of the Highway Salvage Paleontology

608 GEODIVERSITAS • 2008 • 30 (3) New Miocene Heteromyidae (Mammalia, Rodentia)

Program, sponsored by UNSM and the Nebraska Geomyoid rodents from the early Hemingfordian State Department of Roads. Th e FAM specimen was (Miocene) of Nebraska. Annals of Carnegie Museum graciously loaned by Dr J. Flynn of the American 59: 25-47. LINDSAY E. H. 1972. — Small fossils from the Museum of Natural History. Permission to study the Barstow Formation, California.University of California Recent mammal collections was granted by Drs J. Publications in Geological Sciences 93: 1-104. Wible (CM) and R. McPhee (American Museum REEDER W. G. 1960. — A new genus (family of Natural History, New York). Dr C. E. Mitchell of Heteromyidae) from the Tick Canyon Formation of the Geo logy Department SUNY at Buff alo provided California. Bulletin of the Southern California Academy of Sciences 50: 121-132. the camera-lucida for the illustrations and guided the RENSBERGER J. M. 1973. — Pleurolicine rodents (Geo- processing of the PAUP analysis. Dr W. Hallahan myoidea) of the John Day Formation, Oregon. Uni- of the Biology Department, Nazareth College of versity of California Publications in Geological Sciences Rochester provided equipment and assistance for 102: 1-95. the photographs in Figure 4. Dr C. Carrasco of the SUTTON J. F. & KORTH W. W. 1995. — Rodents (Mam- malia) from the Barstovian (Miocene) Anceney lo- Foreign Language Department, Nazareth College of cal fauna, Montana. Annals of Carnegie Museum 64: Rochester assisted in the translation of the title and 267-314. abstract. Photographs for Figures 1 and 3 were taken WAHLERT J. H. 1974. — Th e cranial foramina of protrogo- by G. Brown of UNSM in the Biodiversity Synthesis morphous rodents; an anatomical and phylogenetic Laboratory which was funded in part by National study. Bulletin of the Museum of Comparative Zoology, Harvard 146: 363-410. Science Foundation grant NSF-DBI 050076. Th is WAHLERT J. H. 1983. — Relationships of the Floren- manuscript was critically read by Drs J. H. Wahlert tiamyidae (Rodentia, ) based on cranial and T. S. Kelly. and dental morphology. American Museum Novitates 2769: 1-23. WAHLERT J. H. 1985. — Skull morphology and rela- tionships of geomyoid rodents. American Museum REFERENCES Novitates 2819: 1-20. WAHLERT J. H. 1991. — Th e Harrymyinae, a new hetero- GAZIN C. L. 1932. — A Miocene mammalian fauna from myid subfamily (Rodentia, Geomorpha) based on southeastern Oregon. Carnegie Institute of Washington cranial and dental morphology of Harrymys Munthe, Publications 418: 37-86. 1988. American Museum Novitates 3013: 1-23. HAFNER J. C. & HAFNER M. S. 1983. — Evolutionary WAHLERT J. H. & SOUSA R. A. 1988. — Skull morphology relationships of heteromyid rodents. Great Basin of Gregorymys and relationships of the Entoptychinae Naturalist Memoirs 7: 3-29. (Rodentia, Geomyidae). American Museum Novitates JAMES G. T. 1963. — Paleontology and nonmarine 2922: 1-13. stratigraphy of the Cuyama Valley badlands, Cali- WILLIAMS D. F., GENOWAYS H. H. & BRAUN J. K. 1993. — fornia. Part 1, Geology, faunal interpretations, and and systematics. Special Publication of the systematic descriptions of Chiroptera, Insectivora, American Society of Mammalogists 10: 38-196. and Rodentia. University of California Publications WILSON D. E. AND REEDER D. M. 1993. — Mammal in Geological Sciences 45: 1-154. Species of the World: A Taxonomic and Geographic Ref- KORTH W. W. 1979. — Geomyoid rodents from the erence. Smithsonian Institution Press, Washington, Valentine Formation of Knox County, Nebraska. D.C., 1206 p. Annals of Carnegie Museum 48: 287-310. WOOD A. E. 1935. — Evolution and relationships of KORTH W. W. 1993. — Review of the Oligocene (Orel- the heteromyid rodents with new forms from the lan and Arikareean) genus Tenudomys Rensberger Tertiary of western North America. Annals of Carnegie (Rodentia: Geomyoidea). Journal of Vertebrate Paleon- Museum 24: 73-262. tology 13: 335-341. WOOD A. E. 1936. — A new subfamily of heteromyid KORTH W. W. 1997. — A new subfamily of primitive rodents from the Miocene of western United States. pocket mice (Heteromyidae, Rodentia) from the American Journal of Science 31: 41-49. middle Tertiary. Paludicola 1: 33-66. KORTH W. W. 1998. — Cranial morphology of two Tertiary pocket mice, Perognathus and Cupidinimus (Rodentia, Heteromyidae). Paludicola 1: 132-142. Submitted on 9 July 2007; KORTH W. W., BAILEY B. E. & HUNT R. M. 1990. — accepted on 26 October 2007.

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