Rodents and lagomorphs (Mammalia) from the Hemphillian (late Miocene) of Utah

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1 Journal of Vertebrate Paleontology ISSN: (Print) (Online) Journal homepage: Rodents and lagomorphs (Mammalia) from the Hemphillian (late Miocene) of Utah William W. Korth & Donald D. De Blieux To cite this article: William W. Korth & Donald D. De Blieux (2010) Rodents and lagomorphs (Mammalia) from the Hemphillian (late Miocene) of Utah, Journal of Vertebrate Paleontology, 30:1, , DOI: / To link to this article: Published online: 28 Jan Submit your article to this journal Article views: 272 Citing articles: 3 View citing articles Full Terms & Conditions of access and use can be found at

2 Journal of Vertebrate Paleontology 30(1): , January by the Society of Vertebrate Paleontology ARTICLE RODENTS AND LAGOMORPHS (MAMMALIA) FROM THE HEMPHILLIAN (LATE MIOCENE) OF UTAH WILLIAM W. KORTH,1 and DONALD D. DE BLIEUX 2 1 Rochester Institute of Vertebrate Paleontology, 265 Carling Road, Rochester, New York 14610, U.S.A, wwkorth@frontiernet.net; 2 Utah Geological Survey, P.O. Box , Salt Lake City, Utah 84114, U.S.A ABSTRACT Four species of rodents (two heteromyids and two cricetids) and one lagomorph are identified from the late Tertiary Sevier River Formation of Utah. The heteromyids include a new genus and species of heteromyine, Metaliomys sevierensis, which is intermediate in morphology between the Clarendonian and early Hemphillian Diprionomys Kellogg and the extant genera Liomys and Heteromys. A single specimen is referred to Diprionomys sp., cf. D. minimus (Kellogg). The cricetid Paronychomys lemredfieldi Jacobs is known from the Hemphillian of Arizona. The second cricetid is referred to a new genus Basirepomys. Peromyscus pliocenicus Wilson from the Hemphillian of California is designated as the type species of the new genus, to which the new species B. robertsi from Utah is referred. Basirepomys is viewed as intermediate between Peromyscus and the basal neotomyine Repomys May from the late Hemphillian and Blancan. The only lagomorph in the fauna is Hypolagus vetus (Kellogg). Four of the taxa recognized from the Sevier River Formation (Diprionomys, Paronychomys lemredfieldi, Basirepomys, and Hypolagus vetus) are elsewhere known from the Hemphillian of North America. However, it is not possible at this time to determine whether the fauna is early or late Hemphillian. INTRODUCTION The fossils described here were found in the Sevier River Formation of central Utah and are the first vertebrate fossils to be described from this formation. In addition to the well-preserved rodent and lagomorph fossils, other mammal fossils have been collected from this site, including camelids, felids, mustelids, and gomphotheres (DeBlieux et al., 2002). Miocene fossil sites are rare in Utah so these fossils fill an important geographic gap in the Miocene fossil record of the western U.S. The nearest Miocene sites are located approximately 240 km to the west in the late Hemphillian to early Blancan Panaca Formation of eastern Nevada (Reynolds and Lindsay, 1999; Carrasco et al., 2005). The only Miocene fossils reported to date from Utah are those of the late Hemingforidan to middle Clarendonian Salt Lake Formation in Box Elder County in the northwestern corner of the state (Tedrow and Robison, 1999), and an isolated camel jaw from the Hemingfordian of the Moroni Formation of central Utah (Constenius and Dawson, 2008). To the east, the nearest Miocene fossil bearing rocks are those of the Barstovian Browns Park Formation of northwestern Colorado (Honey and Izett, 1988). Locality 42Sv066v is located on U.S. Forest Service land in a gulley northwest of the town of Sevier, Utah. The fossils occur in several horizons within a narrow band (<10 m) in a tan tuffaceous siltstone. The fossils described here come from two locations (Fig. 1, areas A and C) separated laterally by approximately 40 m. We suspect that these are at the same stratigraphic level but have not yet been able to determine this conclusively because of minor local faulting. The site is located in the upper part of the Sevier River Formation, which is finer grained than the lower part of the formation. In 1996, this site was brought to the attention of then state paleontologist David Gillette by Jeff and Denise Roberts of Annabella, Utah. A small surface collection was made at this time. A team from the Utah Geological Survey (UGS) returned to this site during the spring of 2002 and found bone occurring * Corresponding author. in several horizons. We received an excavation permit from the U.S. Forest Service in the summer of Teams from the UGS led by one of us (D.D.) have been continuing excavations at this site and have now collected several hundred vertebrate fossils. In addition to the cranial and dental remains described here, numerous rodent and lagomorph postcrania have been collected. Further investigation of the geology and taphonomy of the site is currently underway. Dental nomenclature for heteromyid rodents follows that of Korth and Branciforte (2007); for cricetids follows that of Wood and Wilson (1936); and for lagomorphs follows that of Dawson (1958) and White (1987). Upper teeth are designated by capital letters, lower teeth by lowercase letters. Institutional Abbreviations UCMP, University of California Museum of Paleontology; UMNH VP, Utah Museum of Natural History. GEOLOGY The study area lies in the Marysvale volcanic field. Structurally, this area lies in a transition zone between the relatively undeformed Colorado Plateau to the east and the complexly deformed Basin and Range to the west (Rowley et al., 2002). Volcanic rocks in this region range from 32 Ma (Oligocene) to 0.5 Ma (Pleistocene). The Sevier River Formation consists of moderately indurated sandstone, pebbly to bouldery conglomerate, mudstone, and siltstone of fluvial and locally lacustrine origin (Callaghan, 1938). The thickness of the exposed portion of the formation is estimated to be 100 m but may be several hundred meters thick (Rowley et al., 2002). This formation was deposited in basins that are thought to have formed prior to the main episode of Basinand-Range faulting (Rowley, 1998). Fission track dates from airfall tuff beds in the vicinity of the study area range from 14 to 7 Ma (Stevens et al., 1979). Basalt flows that intertongue with Sevier River Formation just west of the study area have K-Ar dates of 9 to 7 Ma (Best et al., 1980). The formation is cut by Miocene- Quaternary Basin-and-Range faults (Rowley et al., 2002). 226 Published online 28 Jan 2010

3 KORTH AND DE BLIEUX HEMPHILLIAN OF UTAH 227 TABLE 1. Dental measurements of Metaliomys sevierensis. Measurements in mm. Abbreviations: L, length (anteroposterior); W, width (transverse). FIGURE 1. Overview of locality UGS 42Sv066v showing the three areas from which fossils have been recovered. Rodent and lagomorph specimens are from quarries A and C. UMNH VP no i1 L i1 W dp4 L 1.62 dp4 W 0.97 p4 L P4 L 1.72 p4 W P4 W 1.64 m1 L M1 L 0.97 m1 W M1 W 1.45 m2 L M2 L 0.71 m2 W M2 W 1.28 m3 L M3 L 0.65 m3 W M3 W 0.89 p4 m3 L P4 M3 L 4.10 Geologists studying this region have focused primarily on the volcanic rocks so a great deal remains to be learned about this formation. SYSTEMATIC PALEONTOLOGY Order RODENTIA Bowdich, 1821 Family HETEROMYIDAE Gray, 1868 Subfamily HETEROMYINAE Gray, 1868 METALIOMYS, n. gen. Type and Only Species Metaliomys sevierensis n. sp. Occurrence Hemphillian (late Miocene) of Utah. Diagnosis Small heteromyine, near size of Liomys; cheek teeth mesodont, higher crowned than perognathines but lower crowned than species of Liomys and Heteromys; cusps of molars remain distinct after occlusion of the premolars (cusps indistinguishable in Liomys and Heteromys before occlusion of the premolars); metalophid of p4 narrower than hypolophid and consists of two major cusps (protostylid, metaconid) with small, central, compressed protoconid (less complex than in Liomys and Heteromys); metalophid does not fuse with hypolophid on p4, leaving deep transverse central valley; lingual stylar cusps on M2 and M3 fuse together in early wear blocking the central transverse valley (lophs remain unfused lingually and valley is continuous in Liomys and Heteromys); ridgeon mandiblemarkinganteriorextent of masseteric scar ends anteriorly well posterior to mental foramen (even with mental foramen in Liomys and Heteromys); ascending ramus of the mandible originates more posteriorly than in Liomys and Heteromys. Etymology Greek, meta, near;andliomys, closely related genus of Recent heteromyine. METALIOMYS SEVIERENSIS, n.sp. (Fig. 2; Table 1) Type Specimen UMNH VP 18748, left mandible with incisor and p4 m3. Referred Specimens UMNH VP 18746, left mandible with incisor and dp4 m1; UMNH VP 18753, partial left mandible with incisor and p4 m1; UMNH VP 19408, maxilla with P4 M3; UMNH VP 19409, left mandible with incisor and p4 m3. Horizon and Locality Hemphillian (late Miocene), Utah Geological Survey site (UGS) 42Sv066v, Sevier River Formation, Sevier County, Utah. Diagnosis Only species of the genus. FIGURE 2. Dentition and mandible of Metaliomys sevierensis. A, UMNH VP 19408, left P4 M3. B C, UMNH VP (holotype). B, occlusal view left p4 m3. C, lingual view. D, UMNH VP 18753, left p4 m1 (part). E, UMNH VP 18746, left dp4 m1. F, UMNH VP (holotype), lateral view of mandible. Scale bars equal 1 mm.

4 228 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 1, 2010 Etymology Latin suffix, -ensis denoting place; and Sevier in reference to the Sevier River Formation. Description The upper cheek teeth decrease in size from P4 to M3. The upper cheek teeth are similar in crown-height to the lower cheek teeth. Also, as in the lower cheek teeth, even though P4 shows signs of early wear, the cusps on the molars are still distinguishable. P4 is the largest of the upper cheek teeth. The protoloph and metaloph are separated by a very deep valley. The protoloph consists mainly of a large protocone that is transversely elongated. Near the apex of the protocone is a minute cuspule that will likely disappear after slightly more wear. Along the buccal slope of the protocone is another minute cuspule about half way to the base of the cusp. On the lingual side is yet another cuspule that is about one-third of the way down the side of the cusp from the occlusal surface. It appears that as the tooth wears towards its base, the protocone (protoloph) will widen, similar to the condition in Recent Liomys. The metaloph consists of three cusps (metacone, hypocone, entostyle) that form a loph that is gently concave anteriorly. The hypocone is the largest of the cusps and is central to the loph. The metacone is more closely positioned to the hypocone than the entostyle. The entostyle is slightly larger than the metacone and is obliquely compressed. M1 consists of the typical heteromyid morphology of two rows of three cusps each. The tooth is nearly 1 1/2 times wider than long. All of the cusps are clearly distinguishable. The protoloph cusps form a straight, transverse line, whereas the cusps of the metaloph form a slightly curved (anteriorly concave) loph. The central transverse valley is very deep but is blocked lingually. The protocone and hypocone are the largest cusps of the tooth and are central. The lingual styles and buccal cusps are nearly equal in size. M2 is much smaller than M1 and is oval in occlusal outline. The occlusal morphology of M2 is similar to that of M1 except that the lingual styles have fused into a single anteroposteriorly elongated cusp that blocks the central transverse valley lingually. The other cusps are distinguishable. M3 is the smallest of the upper cheek teeth and nearly circular in occlusal outline, being slightly wider than long. The cusps of the protoloph are more reduced than in M1 and M2, but are distinguishable. Only the metacone can be recognized on the metaloph. The central transverse valley present on the more anterior molars is reduced to a central pit on M3. The lophs are united both lingually and buccally forming a ring around the central valley. The mandible is slender, typical of heteromyids. The diastema is shallow, equal in length to approximately three-fourths the length of the tooth row. The mental foramen is single and small, aligned with the center of the diastema, at mid-depth of the mandible. The masseteric scar is marked by a faint ridge along the base of the mandible and rises to a point just anterior to the anterior margin of p4, where it forms a small ridge well below the alveolar margin, posterior and slightly dorsal to the mental foramen. The ascending ramus rises dorsally, starting at a point posterior to the tooth row, so all cheek teeth are visible in lateral view. A small coronoid process is present on UMNH VP 18746; it forms a stout hook that extends posteriorly, but is not laterally deflected. Below the coronoid process, at mid-depth of the mandible is a small swelling for the base of the incisor. The angle of the jaw is not completely preserved on any of the specimens, but enough of the posterior margin of the mandible is present to preserve a shallow emargination ventral to the mandibular condyle. The incisor is small and longer than wide. In cross-section, it is flattened medially and rounded laterally, and narrower anteriorly than posteriorly. Enamel extends just over half the lateral side of the incisor. The enamel surface is smooth with no ornamentation. Dp4 is preserved on UMNH VP It is much longer and narrower than any other cheek tooth and heavily worn. The tooth is widest posteriorly and tapers anteriorly. A small anteroconid is present on the anterolingual corner of the tooth and there are three larger cusps along the lingual side, and four smaller cusps along the buccal side. All of the cusps fuse centrally to one another. The cheek teeth are relatively high crowned, higher crowned than in Perognathus or Dipronomys but slightly lower crowned than in Recent heteromyines. The cusps of the molars of Metaliomys remain distinct even after the wear of p4, whereas in specimens of Heteromys and Liomys the cusps are elminated and preplaced by lophs even while the dp4 is still functional (Wood, 1935:fig. 136). The unworn p4 on the type specimen has just come into occlusion (minimal wear on the cusps). The metalophid is much narrower than the hypolophid. The metalophid is dominated by two major cusps, metaconid and protostylid, that are of equal size. The protostylid is anteroposteriorly elongated, whereas the metaconid is circular in occlusal outline. A minute protoconid is present between the two metalophid cusps. It is much smaller than the other cusps and is fused to the buccal side of the metaconid, being separated from the protostylid by a narrow, shallow valley. The hypolophid consists of a widely spaced entoconid (lingual) and hypoconid (buccal). Both cusps are anteroposteriorly compressed. There is a minute hypostylid on the buccal slope of the hypoconid that will likely disappear after only moderate wear. The p4 is heavily worn on UMNH VP The proportions of the tooth and general occlusal outline are the same as in the unworn p4 of the holotype. All cusps have been eliminated on UMNH VP and the two lophs are fused buccally with a deep emargination along the lingual side. The m1 has the typical heteromyid pattern of two transverse rows of three cusps each. On the holotype, there is a minute cuspule at the anterobuccal corner of the tooth that is separated from both the protoconid and the protostylid. On m1 of UMNH VP 18746, there is a short cingulum running anteriorly from the protostylid, ending anteriorly at the same spot as the cuspule on the holotype. The protostylid is nearly as large as the other metalophid cusps (metaconid, protoconid), whereas the hypostylid is much smaller than the cusps of the hypolophid (entoconid, hypoconid). The cusps of the hypolophid are anteroposteriorly compressed. The transverse valley separating the lophs is deep and wide. The second lower molar is similar in occlusal morphology to m1 but smaller in all dimensions. The hypostylid is minute, much smaller than on m1, and the transverse valley is blocked buccally by a low ridge connecting the stylids. The m3 is the smallest of the molars and similar in occlusal pattern. However, the protostylid is reduced to a short ridge at the anterobuccal corner of the tooth (cingulum) and the hypolophid is only two-cusped, the hypostylid being completely absent. Discussion Metaliomys seveierensis is referable to the Heteromyinae as defined by Wood (1935) based on the morphology of p4, where there is no central union of the transverse lophs. It is distinct from the late Clarendonian to early Hemphillian heteromyine Diprionomys in having slightly higher crowned cheek teeth (see Kellogg, 1910; Hall, 1930; Shotwell, 1967b). Metaliomys differs from the extant heteromyines in having slightly lower crowned cheek teeth. In the Recent Heteromys and Liomys, the cusps of the molars are incorporated in the transverse lophs and indistinguishable at a very early age, even when the deciduous premolar is still functional. In Metaliomys, the cusps of the molars are distinct even after the permanent premolar shows wear. The lower premolar of Metaliomys also differs from Recent genera in having a fairly simple metalophid that is narrower (buccolingually) than the hypolophid. In Recent heteromyines, the metalophid is more

5 KORTH AND DE BLIEUX HEMPHILLIAN OF UTAH 229 complex (at least three subequal cusps) and is as wide as or wider than the hypolophid. The central transverse valley of the upper molars remains open at both ends in Liomys and Heteromys until very late wear stages. In Metaliomys, the transverse valley is blocked lingually on all upper molars even at very early stages of wear, and the lingual stylar cusps are fused to one another on both M2 and M3. The mandible of Metaliomys also differs from Recent heteromyines. The masseteric scar on the mandible of M. sevierensis ends anteriorly posterior and slightly dorsal to the mental foramen. In both Recent genera, the masseteric scar ends directly dorsal to the mental foramen, and there is a small ridge running posteriorly from it marking the dorsal limit of the masseteric scar. This latter ridge is lacking in Metaliomys. The ascending ramus in Metaliomys rises from the horizontal ramus more posteriorly than in Recent heteromyines. In Metaliomys all of the molarsare visible in lateral view, but in Recent heteromyines the ascending ramus blocks m3 from lateral view. Among Tertiary species, M. sevierensis is closest in morphology to Diprionomys from the Clarendonian and early Hemphillian. Both species of Diprionomys, D. parvus and D. minimus, have lower-crowned cheek teeth than Metaliomys, and occur earlier. The species of Diprionomys also have the heteromyine-like morphology of the premolar (Kellogg, 1910; Hall, 1930; Wood, 1935, 1936; Shotwell, 1967b), and are known only from Nevada and Oregon. This suggests that Recent heteromyines may have arisen from a lineage that began in the Clarendonian with Diprionomys, gone through a stage such as represented by Metaliomys in the Hemphillian, and finally attained the hypsodonty and premolar morphology of the extant genera. The earliest record of the Recent genera is Liomys from the Pleistocene of Mexico (Korth, 1994). DIPRIONOMYS Kellogg, 1910 DIPRIONOMYS sp., cf. D. MINIMUS (Kellogg, 1910) (Fig. 3) Entoptychus minimus Kellogg, 1910 Diprionomys minimus (Kellogg) Wood, 1936 Referred Specimen UMNH VP 19410, partial left mandible with incisor and p4 m1. Measurements i1: L = 0.90 mm, W = 0.54 mm; p4: L = 1.15 mm, W = 1.17 mm; m1: L = 1.11 mm, W = 1.14 mm. Horizon and Locality Referred specimen from Hemphillian (late Miocene), UGS site 42Sv066v, Sevier River Formation, Sevier County, Utah. Description The mandible is very slender and the diastema is long (3.3 mm) and extremely shallow, barely dipping below the alveolar margin of the molars. The mental foramen is just below the center of the diastema, closer to the dorsal margin of the diastema than the base of the mandible. The masseteric scar extends anteriorly well past the alveolus for p4 for about half the length of the diastema and ends just posterior to the mental foramen and just dorsal to it. The incisor is very narrow (transversely) and rounded along the anterior enamel surface. There is no ornamentation on the enamel. The cheek teeth of UMNH VP are heavily worn, so no individual cusps are recognizable. The lower premolar is nearly equidimensional. The metaloph consists of an obliquely oriented oval fossettid that nearly touches the hypolophid buccally, but the central transverse valley is continuous for the entire width of the tooth. The hypolophid is an anteroposteriorly compressed, transverse loph that is only slightly wider than the metalophid. The m1 is slightly smaller in dimensions than p4 and consists of two transverse lophs that are equal in size. The two lophs are united buccally as well as lingually, just buccal to the lingual ends of the lophs. This union of the lophs produces a minute, circular enamel lake in the center of the occlusal surface. Because the cheek teeth are heavily worn, there is very little enamel left on FIGURE 3. Dentition and mandible of Diprionomys sp., cf. D. minimus from the Sevier River Formation Utah, UMNH VP A, occlusal view of p4 m1. B, lateral view of mandible. Scale bars equal 1 mm. the lateral size of the teeth, but it is evident from the remaining enamel, that there are no enamel chevrons or dentine tracts present on the teeth. Discussion Diprionomys minimus is known only from the type specimen, UCMP 12569, from the early Hemphillian Thousand Creek fauna of Nevada. UMNH VP is tentatively referred to this species because it is similar in size (Wood, 1936:115), and has the distinctive heteromyine morphology of p4 where the metalophid remains unfused to the hypolophid. In Wood s (1936) emended diagnosis of the species, he notes that the premolar is nearly equal in size to the molars. This is also true for UMNH VP The morphology of the masseteric scar on Diprionomys parvus was figured by Shotwell (1967b:fig. 10D) and is more similar to that of UMNH VP than to that of M. sevierensis, but does not extend quite as far anteriorly as on UMNH VP UMNH VP cannot definitely be referred to D. minimus because the metalophid is narrower than on the type specimen, and there is no indication of a third metalophid cusp. UMNH VP is distinct from specimens of Metaliomys sevierensis in proportions of the cheek teeth and morphology of the mandible. The p4 and m1 of M. sevierensis are markedly shorter than wide, whereas those of UMNH VP are nearly equal in dimensions. The lower premolar of M. sevierensis is also clearly smaller than m1, whereas in UMNH VP 19410, p4 is nearly equal in size to m1, and even slightly larger. The diastema of UMNH VP is longer (3.3 mm) than that of the holotype of M. sevierensis (2.7 mm), even though the two specimens are similar in other dimensions of the mandible and dentition. The masseteric scar on the mandible of specimens of M. sevierensis ends anteriorly well short of the mental foramen, just anterior to the alveolus for p4. In UMNH VP 19410, the masseteric scar extends for nearly half the length of the diastema, and ends just short of the mental foramen, much farther anterior than in any specimens of M. sevierensis. The mental foramen on the mandible of M. sevierensis is situated at about mid-depth of the mandible, even with the center of the diastema (Fig. 2F). In UMNH VP 19410, the mental foramen is even with the center of the diastema, but very close to the dorsal margin of the diastema.

6 230 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 1, 2010 FIGURE 4. Dentition and mandible of Paronychomys lemredfieldi from the Sevier River Formation, Utah. A, UMNH VP 18750, right M1 M3. B C, UMNHVP B, occlusal view, right m1 m3. C, medial view of mandible. Scale bars equal 1 mm. The fusion of the lophs of the cheek teeth on UMNH VP also differs from those of M. sevierensis. Even though the cheek teeth of UMNH VP are very heavily worn, the two lophs remain distinct on p4, whereas in worn specimens of M. sevierensis the lophs fuse buccally. The m1 of UMNH VP retains a small enamel lake at the center of the occlusal surface, the transverse lophs having united both lingually and buccally, similar to worn molars of D. parvus (Shotwell, 1967b):fig. A). In the heavily worn molars of M. sevierensis, the lophs are united for their entire length. CRICETIDAE Fischer de Waldheim, 1817 PARONYCHOMYS Jacobs, 1977 PARONYCHOMYS LEMREDFIELDI Jacobs, 1977 (Fig.4;Table2) Referred Specimens UMNH VP 1847, mandible with incisor and m1 m3; UMNH VP 18765, isolated m2; UMNH VP 1854, 1850, maxillae with M1 M3. Horizon and Locality Referred specimens from Hemphillian (late Miocene), UGS site 42Sv066v, Sevier River Formation, Sevier County, Utah. Description Both maxillae present have little to moderately worn cheek teeth, so it is evident that the cusps of the teeth are higher than those of P. woodburnei (Martin, 2008), but lower than thoseof P. alticuspis (Baskin, 1979). M1 is much longer than the other upper molars. The cusps are alternating (paracone directly connected to hypocone) and there are no accessory lophs or cuspules in the valleys separating the major cusps. The lingual cusps (protocone, hypocone) are crescentic in shape and the buccal cusps (paracone, metacone) are oval and obliquely oriented, anterobuccally to posterolingually. The anterocone is on the buccal half of the tooth and similar in shape to the other buccal cusps. There is a low ridge descending from the lingual side of the anterocone that wears to a small notch between it and the protocone. M2 is similar to M1 in occlusal morphology but is much shorter. The anterocone is replaced by a short anterior cingulum on M2 that originates near the center of the anterior margin of the tooth but does not quite reach the buccal margin. Lingually, the anterior cingulum also has a ridge running buccally as does the anterocone on M1. M3 is much smaller than M2 and nearly circular in occlusal outline. The anterior cingulum and protocone are as in M2, but the paracone attaches via a short loph anteriorly to the junction of the anterior arm of the protocone and base of the anterior cingulum, and posteriorly to the hypocone. The paracone is circular rather than oval in outline. The hypocone is greatly reduced in size, appearing as a small swelling on the posterolingual corner of the tooth. A short posterior cingulum originates from the hypocone and wraps around the posterobuccal corner of the tooth, ending anteriorly along the buccal border just posterior to the paracone. There is no evidence of a metacone. The medial side of the mandible is preserved on UMNH VP The mandible is slender and the diastema is shallow but long, being nearly equal in length to the tooth row. There is a broad valley separating the tooth row from the ascending ramus. The lower incisor is delicate and much longer than wide. The enamel surface of the incisor is smooth. The m1 is the longest of the lower molars. As in the upper molars, the cusps are high and alternating (protoconid continuous with the entoconid). The buccal cusps (protoconid, hypoconid) are crescentic and the lingual cusps (metconid, entoconid) are oval and obliquely oriented anterobuccal to posterolingual. As in the upper molars, there are no lophids or cuspules in the deep valleys that separate the cusps. The anteroconid is mainly on the buccal side of the tooth and closely appressed to the metaconid, separated from it by a small enamel lake. There is a small notch separating the buccal end of the anteroconid from the protoconid. A short posterior cingulum arises from the hypconid and extends lingually, ending well sort of the lingual margin of the tooth. The m2 is shorter than m1 and the major cusps are of a similar morphology. The anteroconid is lacking on m2, but a short anterior cingulum runs buccally from the anterior arm of the protoconid along the anterior margin of the tooth. The m3 is the smallest of the molars. It is wider anteriorly than posteriorly. The metaconid and protoconid are joined anteriorly along the anterior margin of the tooth. Posteriorly, the protoconid is continuous to entoconid on the lingual margin of the tooth. The entoconid is greatly reduced in size. The hypoconid is TABLE 2. Dental measurements of Paronychomys lemredfieldi from the Sevier River Formation, Utah. Measurements in mm. Abbreviations as in Table 1. UMNH VP no. M1 L M1 W M2 L M2 W M3 L M3 W M1 M3 L m1 L m1 W m2 L m2 W m3 L m3 W m1 m3 L

7 KORTH AND DE BLIEUX HEMPHILLIAN OF UTAH 231 also minute, but remains crescentic in shape. The hypconid connects to the entoconid both anteriorly and posteriorly, forming a small lake. Discussion The specimens from the Sevier River Formation are nearly identical to the topotypic material of Paronychomys lemredfieldi described from Arizona (Jacobs, 1977). The only difference is that the anteroconid on the m1 of the Utah material is slightly closer to the metaconid than in the type material. This is viewed as a minor individual variation. P. lemredfieldi (including the type material and referred specimens from Utah) is smaller than P. tuttlei and P. woodburnei and larger than P. alticuspis (Jacobs, 1977:tables 6 and 8; Baskin, 1979:table 7; Martin, 2008:table 9), and the cheek teeth are higher-crowned than those of P. woodburnei, but lower-crowned than those of P. alticuspis. BASIREPOMYS,n.gen. Type Species Peromyscus pliocenicus Wilson, Referred Species B. robertsi,n.sp. Diagnosis Large cricetid rodent (larger than Peromyscus); mesodont cheek teeth (higher crowned than Peromyscus, lower crowned than Repomys); accessory cuspules and lophs absent or greatly reduced on cheek teeth; anterocone on M1 and anteroconid on m1 broad (buccolingually) or doubled; alternation of cusps complete on m1, but not complete on unworn M1 (hypocone not directly connected to paracone). Etymology Greek, basis, foundation or beginning; and Repomys, a closely related genus. Discussion Wilson (1937) first described Peromyscus pliocenicus from the early Hemphillian of California, distinguishing it from other species of Peromyscus by its larger size and higher-crowned cheek teeth. Since that time, a number of specimens have been referred to P. cf. pliocenicus from the early Hemphillian of Oregon (Shotwell, 1967a) and Nebraska (Korth, 2004) and the late Hemphillian of California (May, 1981; also see Lindsay, 2008). May (1981) noted the similarity of P. pliocenicus to the latest Hemphillian and Blancan primitive neotomyine Repomys, and suggested that it was the likely ancestor of the latter. Korth (1994) suggested that P. pliocenicus could be referred to a new genus based on the morphologies cited by Wilson (1937) and the probable relationships proposed by May (1981) but failed to do so. Here, Basirepomys is proposed as a genus to include P. pliocenicus and the additional specimens referred elsewhere to P. cf. pliocenicus. Basirepomys differs from contemporaneous cricetids and Peromyscus in its large size and greater crown-height of the cheek teeth. It also differs fromperomyscus and other Hemphillian and later cricetids in not having a direct connection of the hypocone to the paracone on M1. In other cricetids the anterior arm of the hypocone is obliquely oriented and directly continuous with the paracone, whereas in Basirepomys there is a slight wrinkle in the anterior arm of the hypocone that allows for the connection of the metacone before continuing anteriorly on to the paracone. This connection in species of Basirepomys is only evident in the early stages of wear. After moderate wear, the lophs broaden and the connection of the hypocone to paracone appears to be direct. BASIREPOMYS ROBERTSI,n.sp. (Fig. 5; Table 3) Type Specimen UMNH VP 18751, right mandible with incisor and m1 m2. Referred Specimens UMNH VP 18749, left maxilla with heavily worn M1 M3; UMNH VP 18761, fragmentary rostrum with right I1; 18762, left maxilla with M1 M2; UMNH VP 18763, maxillary fragment with partial left M1; UMNH VP 18752, two fused mandibles with incisors, right m1 m3 and left m1 m2; UMNH VP 18755, two fused mandibles with complete dentition (molars worn); UMNH VP 18764, left m1; UMNH VP 19411, right mandible with incisor and m1 m3; UMNH VP 19412; right partial mandible with incisor and m1 m2. Horizon and Locality Hemphillian (late Miocene), UGS site 42Sv066v, Sevier River Formation, Sevier County, Utah. Diagnosis Cheek teeth smaller and lower-crowned than in thetypespeciesb. pliocenicus; anterocone on M1 a single, broad cusp; anteroconid on m1 doubled. Etymology Patromym for Jeff and Denise Roberts who discovered site 42Sv066v and alerted David Gillette, Utah State Paleontologist, in Description UMNH VP preserves a small portion of the rostrum consisting of the right premaxillary bone and fragments of the maxilla and the right upper incisor. This specimen is referred to B. robertsi based on myomorphous zygomasseteric structure and size (largest species of cricetid). The premaxillarymaxillary suture runs irregularly down the side of the rostrum. The rostrum is clearly myomorphous because the infraorbital foramen is high on the side of the rostrum and limited ventrally, suggesting a relatively high zygomatic plate. The incisive foramen FIGURE 5. Dentition, mandible and rostrum of Basirepomys robertsi. A, UMNH VP 18749, left M1 M2. B, UMNH VP (holotype), right m1 m2. C, UMNH VP 18752, right m3. D, UMNH VP 18755, right m1 m2. E, UMNH VP 18761, lateral view of right rostral fragment with I1. F, UMNH VP (holotype), lateral view of mandible. Abbreviations: inf, incisive foramen; iof, infraorbital foramen. Scale bars equal 1 mm.

8 232 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 1, 2010 TABLE 3. Dental measurements of Basirepomys robertsi. Abbreviations as in Table 1. Statistical abbreviations: M, mean; SD, standard deviation; CV, coefficient of variation. Measurements in mm. UMNH VP no. M1 L M1 W M2 L M2 W M3 L M3 W M1 M3 L m1 L m1 W m2 L m2 W m3 L m3 W m1 m3 L (left) (right) (left) (right) M SD CV is preserved on the ventral side posterior to the incisor. It is not greatly enlarged or reduced. The incisor is broadest anteriorly and nearly flat on the enamel surface. Enamel extends onto only about one-fourth the lateral side of the tooth. The cheek teeth are mesodont, but higher crowned than in species of Peromyscus. A ratio of the height of the protoconid versus the length of m1 of unworn or little worn specimens was used for comparison of crown height. In species of Recent Peromyscus (P. maniculatus, P. leucopus, P. guatamalensis)thisratio ranged from 0.29 to 0.50 with an average of In the holotype of the Hemphillian P. antiquus, contemporaneous with Basirepomys, the ratio is Specimens of Basirepomys (including topotypic material of B. pliocenicus) ranged from 0.50 to The height of the cheek teeth is also evident in worn specimens of Basirepomys because of the nearly vertical sides of the molar. In species of Peromyscus the sides of the molars always taper toward the occlusal surface. M1 is the largest of the upper molars. The anterocone is large and situated on the buccal side of the tooth. It is a single cusp, but there is a minute groove along the anterolingual surface of the tooth that makes the cusp look doubled in early wear. It is evident that this groove will disappear after moderate wear. The lingual cusps (protocone, hypocone) are crescentic in occlusal outline, and the buccal cusps (paracone, metacone) are round to slightly oval in outline. The alternation of cusps is not complete on the upper molars at early stages of wear. On M1, the paracone and protocone are even with one another and the posterior arm of the paracone meets the posterior arm of the protocone anterior to the center of the tooth, rather than the posterior arm of the paracone running directly to the hypocone, as in cricetids, which have completely alternating cusps. In the central transverse valley ofthetypeofb. robertsi is a low mesoloph that runs to the buccal edge of the tooth, ending in a minute mesostyle. The metacone is completely isolated from the other cusps. The posterior cingulum runs along the posterior border of the tooth from the hypocone, ending buccally on the posterobuccal corner of the metacone. M2 is similar in morphology to M1, but the enlarged anterocone is replaced by a minute anterocone along the anterior margin of the tooth, continuous with an anterior cingulum that wraps around the anterobuccal corner of the tooth. The mesoloph on M2 does not reach the buccal margin of the tooth as in M1, but there is a distinct mesostyle present. There is no specimen that preserves M3, but the two roots of M3 are present on UMNH VP M3 is markedly smaller than the anterior molars and is roughly triangular in shape. The mandible is best preserved in the type specimen. It is generally slender in shape. The diastema dips well below the alveolar margin and is approximately half the length of the tooth row. The mental foramen is high on the mandible, just below the dorsal margin of the diastema, just anterior to the anterior root of m1. There is a slight digastric process ventral to the mental foramen. The masseteric scar is V-shaped and ends anteriorly below the center of m1, just above mid-depth of the mandible. The ascending ramus rises gradually posteriorly, blocking only m3 from lateral view. The coronoid process is a small hook that is not deflected medially or laterally. There is a low ridge of bone running from a point below the coronoid process posterodorsally to the mandibular condyle. The angle of the mandible is not preserved on any specimens. The lower incisor is flattened medially and rounded laterally, giving the cross-section a D-shape. It is wider near the anterior end of the cross-section than posteriorly. Smooth enamel reaches about one-third the lateral side of the tooth. The m1 is the largest of the lower molars. The anteroconid is large and doubled on all specimens. The two lobes of the anteroconid are subequal in size. Both the metaconid and protoconid join the anteroconid near its center and are not directly connected to one another. There is a small ridge running from the buccal corner of the buccal lobe of the anteroconid to the base of the tooth, producing a small anterior cingulum. Similar to the upper molars, the buccal cusps (protoconid, hypoconid) are crescentic to triangular in shape, and the lingual cusps (metaconid, entoconid) are oval and obliquely oriented (posterolingual to anterobuccal). Unlike the upper molars, the alternation of the cusps is complete on the lower molars. The posterior arm of the protoconid is connected to the entoconid. However, on the type specimen (the least worn) there is a slight wrinkle in the posterior arm of the protoconid just before it joins the entoconid, from which runs a minute mesolophid that disappears almost immediately into the valley between the lingual cusps. On all of the referred specimens that are more worn, this wrinkle has been eliminated by wear and there is no sign of a mesolophid. The short posterior cingulum runs from the hypoconid along the posterior side of the tooth to the posterolingual corner. Other than the minute mesolophid on the holotype, there are no accessory lophs or stylids on any of the lower molars. The m2 is similar to m1 in morphology, but lacks the large, twinned anteroconid. The metaconid is at the anterolingual corner of the tooth and a loph runs along the anterior margin of the tooth from it for the entire width of the tooth, ending buccally at the base of the anterobuccal corner of the tooth, producing a distinct anterior cingulum on the buccal half. The protoconid is directly connected to the entoconid without a mesolophid. The only other difference between m2 and m1 is that the posterior arm of the hypoconid runs on m2 posterolingually to the corner

9 KORTH AND DE BLIEUX HEMPHILLIAN OF UTAH 233 of the tooth, so that there is no transversely running posterior cingulum as in m1. The m3 is the smallest of the molars. The anterior half (metaconid, protoconid, anterior cingulum) is nearly identical to that of m2. The hypoconid and entoconid are greatly reduced in size, making the tooth much narrower posteriorly. The posterior arm of the protoconid is continuous with the entoconid. The hypoconid is round and at the center of the posterior margin of the tooth. It is broadly connected to the entoconid. Discussion Basirepomys robertsi differs from the type species, B. pliocenicus by being slightly smaller and having the cheek teeth not as high crowned. Other specimens that have been referred to Peromyscus cf. pliocenicus from Oregon and California are distinct from both B. robertsi and B. pliocenicus. Specimens referred to P. cf. pliocenicus from the early Hemphillian Drewsey Formation of Oregon (Juniper Creek) were described by Shotwell (1967a). These specimens differ from the topotypic material of B. pliocenicus and B. robertsi in having only a single anteroconid on m1 and having slightly higher-crowned cheek teeth. The Oregon specimens are slightly smaller than those of B. pliocenicus and similar in size to those of B. robertsi (Shotwell, 1967a:table I; Table 3, this paper). Cheek teeth referred to P. cf. pliocenicus from the late Hemphillian Pinole fauna of California by May (1981) are larger and higher-crowned than those of both B. pliocenicus and B. robertsi. The Pinole specimens also have a single anteroconid on m1, as in the Oregon specimens and species of Repomys, unlike the m1s of B. pliocenicus and B. robertsi, which have a twinned anteroconid. Basirepomys robertsi is the eastern-most occurrence of the genus (including specimens referred to Peromyscus cf. pliocenicus) except for a single tooth from the early Hemphillian of northwestern Kansas (Korth, 2004). The Kansas specimen is a single M1 similar in size and crown-height to that of B. robertsi (Korth, 2004:fig. 7D), but a definite species identification cannot be made at this time. The latter is the only recognition of Basirepomys east of the Rocky Mountains. Order LAGOMORPHA Brandt, 1855 Family LEPORIDAE Fischer de Waldheim, 1817 HYPOLAGUS Dice, 1917 HYPOLAGUS VETUS (Kellogg, 1910) (Figure 6; Table 4) Referred Specimens UMNH VP 18756, right p3; UMNH VP 18757, left p3; UMNH VP 18758, partial right mandible with m2 m3; UMNH VP 18759, right P2; UMNH VP 18760, mandibular fragment with lower molariform tooth and isolated upper molariform tooth; UMNH VP 19400, 19403, isolated lower molariform teeth; and UMNH VP , , isolated upper molariform teeth. TABLE 4. Dental measurements of Hypolagus vetus from the Sevier River Formation, Utah. Measurements in mm. Abbreviations: N, number of specimens; M, mean; OR, range of size. Other abbreviations as in Table 1. N M OR p3 L p3 W lower molariform L lower molariform W m3 L m3 W P2 L P2 W upper molariform L upper molariform W FIGURE 6. Dentition of Hypolagus vetus from the Sevier River Formation, Utah. A, UMNH VP 18756, right p3 (reversed). B, UMNH VP 18757, left p3. C, UMNH VP 18759, left P4. D, UMNH VP 18760, left upper molariform tooth. Scale bar equals 1 mm. Horizon and Locality Hemphillian (late Miocene), UGS site 42Sv066v, Sevier River Formation, Sevier County, Utah. Description The p3s are hypsodont and have only two cement-filled re-entrants, the anterior external (AER) and posterior external (PER). The PER is deep, extending 47 54% of the width of the tooth. The thick enamel along the anterior margin of the PER is sigmoid in shape, and the re-entrant is not deflected either anteriorly or posteriorly. The AER extends 15 20% of the total width of the tooth. The lower molariform teeth are typical of leporids; hypsodont, consisting of two transverse lophs, trigonid and talonid. The trigonid is always wider than the talonid. The reentrant valleys between the trigonid and talonid is cement-filled. The last lower molar is markedly smaller than p4 m2. P2 is oval in outline with a deep main anterior re-entrant (MAR) and an external anterior re-entrant (EAR) that is nearly as deep. Both re-entrants are cement-filled. Upper molariform teeth are transversely elongated with a deep cement-filled hypostria that is highly crenulated in outline. Discussion The specimens from the Sevier River Formation referred to Hypolagus vetus do not differ in size or morphology from the type and referred material described by White (1987). Previously, H. vetus has been reported from the Hemphillian of North America west of the Rocky Mountains, and Blancan of California and Baja California (White, 1987). However, in a series of faunal lists from the different horizons in the Ogallala Group in Nebraska, Voorhies (1990) listed H. vetus as occurring throughout the Hemphillian. This suggests that the Utah occurrence is in the center of the range of H. vetus in the Hemphillian. CONCLUSIONS Four of the five taxa of rodents and lagomorphs from the Sevier River Formation (Diprionomys, Paronychomys

10 234 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 1, 2010 lemredfieldi, Basirepomys,andHypolagus vetus) are known elsewhere from the Hemphillian. A Hemphillian age for these fossils fits well with age estimates for these rocks. Hypolagus vetus is known throughout the western U.S. and into Baja California from the Hemphillian and Blancan (White, 1987). Voorhies (1990) has also identified H. vetus from the early to late Hemphillian of Nebraska. Basirepomys (= species referred to Peromyscus cf. pliocenicus) have been identified from the early Hemphillian of Oregon and California (Wilson, 1937; Shotwell, 1967a), the late Hemphillian of California (May, 1981), and a single specimen has been identified from the early Hemphillian of Kansas (Korth, 2004). Similarly, Paronychomys has been cited previously from the late Hemphillian of Arizona, Texas, and Oregon (Jacobs, 1977; Baskin, 1979; Dalquest, 1983; Martin, 2008) and the latest Hemphillian of Nebraska (Voorhies, 1990). However, it has also been documented from the early Hemphillian of California (Whistler and Burbank, 1992). Tedford et al. (2004) identifed Hypolagus vetus and Paronychomys as a taxa typical of the Hemphillian but did not limit them to either the late or early Hemphillian. Diprionomys minimus is known only from the early Hemphillian of Nevada (Kellogg, 1910; Wood, 1936; Flynn et al., 2008). However, because the Sevier River specimen cannot be definitely referred to this species, and the species is limited to only one specimen, it is impossible at this time to use it as an index fossil for the early Hemphillian. Metaliomys sevierensis is unique to the Sevier River Formation and cannot be used in any type of correlation. None of the taxa used as diagnostic for the early or late Hemphillian (Tedford et al., 2004) are present in the Sevier River fauna, so the age of the fauna cannot be determined precisely at present. ACKNOWLEDGMENTS Collection and excavation was done under U.S. Forest Service special use permits FIL 54, FIL 68, FIL 88, and FIL111. Help from the Fish Lake National Forest, Fillmore Ranger District, was provided by Melvin Bolling, Mary Erickson, Bob Leonard, Steve Winslow, and Bill Wright. Forest Service paleontologist Steve Robison is thanked for his assistance and support. For help in the field, we thank Jane DeBlieux, Jerry Harris, Jim Kirkland, Tom Mellenthin, Scott Madsen, Simon Masters, Andrew Milner, George Muller, Phil Policelli, Jeff Roberts, and Denise Roberts. We thank Dave and Janet Gillette for their assistance. Helpful reviews of the manuscript were provided by Rick Allis, Kimm Harty, Martha Hayden, Jim Kirkland, Mike Lowe, and Robert Ressetar. Camera equipment for Figures 2, 4, and 5 was provided by Dr. W. Hallahan of the Biology Department, Nazareth College of Rochester. Camera lucida for illustrations of Figure 6 was provided by Dr. G. McIntosh of the Rochester Museum and Science Center, Rochester, New York. Comparative casts of Hemphillian rodents were provided by Dr. E. Lindsay of the University of Arizona. Field work for WWK funded in part by contributions to the Rochester Institute of Vertebrate Paleontology. LITERATURE CITED Baskin, J Small mammals of the Hemphillian age White Cone local fauna, northeastern Arizona. Journal of Paleontology 53: Best, M. G., E. H. McKee, and P. E. Damon Space-timecomposition patterns of late Cenozoic mafic volcanism, southwestern Utah and adjoining areas. American Journal of Science 280: Bowdich, T An Analysis of the Natural Classifications of Mammalia for the Use of Studenst and Travelers. J. Smith, Paris, 115 pp. Brandt, J. F Beiträge zur nähern Kenntnis der Säugethiere Russlands. Mémoires de l Académie Impériale des Sciences, St. Petersburg, Series 69: Callaghan, E Preliminary report on the alunite deposits of the Marysvale region, Utah. 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Jacobs, L. L Rodents of the Hemphillian age Redington local fauna, San Pedro Valley, Arizona. Journal of Paleontology 51: Kellogg, L Rodent fauna of the late Tertiary beds at Virgin Valley and Thousand Creek, Nevada. University of California Publications, Geological Sciences 5: Korth, W. W The Tertiary Record of Rodents in North America. Plenum Press, New York, 319 pp. Korth, W. W Preliminary determination of the age of the Sappa Creek local fauna, northwestern Kansas. Paludicola 4: Korth, W. W., and C. Branciforte Geomyoid rodents (Mammalia) from the Ridgeview local fauna, early-early Arikareean (late Oligocene) of western Nebraska. Annals of Carnegie Museum 76: Lindsay, E. H Cricetidae; pp in C. M. Janis, G. F. Gunnell, and M. D. Uhen (eds.), Evolution of Tertiary Mammals of North America, Volume 2. Cambridge University Press, New York. Martin, J. E Hemphillian rodents from northern Oregon and their biostratigraphic implications. Paludicola 6: May, S. 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