Pseudaelurus skinneri, ROTHWELL, 2003

ROTHWELL, TOM, 2003, Phylogenetic Systematics of North American Pseudaelurus (Carnivora: Felidae), American Museum Novitates 3403, pp. 1-64 : 21-25

Pseudaelurus skinneri , new species

HOLOTYPE: F:AM 61812, left ramus with

c, p2 alveolus, p3, p4 alveolus and m1.

TYPE LOCALITY: Hilltop Quarry, Sheep Creek Formation, Sioux Co., Nebraska .

REFERRED SPECIMENS: Sheep Creek Fauna, Sheep Creek Formation (late Hemingfordi­ an), Sioux County, Nebraska: F:AM 61814, left partial ramus with c, alveolus of p2, p3– m1, Thistle Quarry; F:AM 61816, left partial ramus with broken c, alveolus of p2, p3– m1,Thistle Quarry; F:AM 61818, left partial ramus with broken alveolus c, alveolus of p2, p3, p4, broken m1, Hilltop Quarry; F:AM 61817, right partial ramus with broken alveolus of c, p3–m1, Long Quarry; F:AM 61810, left partial ramus with broken alveolus of c, alveolus of p2, p3–m1, Greenside Quarry; F:AM 61819, left partial ramus with broken alveolus of c, alveolus of p2, p3–m1, Buck Quarry; and F:AM 61813, maxillary fragment with alveolus of P2, P3–P4, Ashbrook Quarry.

AGE: Late Hemingfordian ( Galusha, 1975; Skinner et al., 1977; Tedford et al., 1987).

DISTRIBUTION: Late Hemingfordian of Nebraska.

ETYMOLOGY: Species name in honor of Morris Skinner, a charter member of the Society of Vertebrate Paleontology who worked for the Frick Laboratory from 1927 to 1973 as a field worker, preparator, and curator.

DIAGNOSIS: Differs from all North American species by its unique size. P. skinneri has an m1 length range of 11.5–13.8 mm, larger than P. stouti . The next largest North American species, P. aeluroides , known only by the type specimen, has an m1 length of 15.6 mm. In size, P. skinneri overlaps only the European species P. lorteti and the Asian species P. cuspidatus and P. guangheensis . Pseudaelurus skinneri can be differentiated from these species by the following combination of characters: shorter c–p3 length, m1 with tall protoconid and reduced metaconid and talonid, P4 protocone projecting at an obtuse angle anterolingually. P. skinneri differs from the European species P. lorteti by a taller m1 protoconid which is consistently much taller than the paraconid. P. skinneri differs from the Asian P. cuspidatus by a shorter c–p3 length, lacking the pronounced anterior cingular cusps on p3 and p4, and by presence of a gently sloping posterior edge of m1. P. skinneri differs from the Asian P. guangheensis by P4 protocone projecting at an obtuse angle anterolingually.

DESCRIPTION AND COMPARISONS OF HOLO­ TYPE: F:AM 61812, the type specimen of P. skinneri , has a dentary that is a well preserved (figs. 22–24). It is slender and gracile. Medially, fine details of a small mandibular symphysis can be seen along the anterior border of the ramus. A large mandibular foramen is positioned medially, beneath the origin of a slender, yet erect, coronoid process (fig. 23). This upright morphology of the coronoid compares favorably with the much larger P. validus , but contrasts with the more sloping processes seen in the later P. intrepidus and P. marshi . The lower canine has a posterior ridge, but the cross section is more elliptical and symmetrical than the medially flattened canine of P. validus . There is no evidence of a p1 as in the specimen of P. cuspidatus ( Wang et al., 1998) . A large single­rooted alveolus for p2 is between c and p3. The alveolus of p2 is slightly closer to p3 than it is to c, and is situated lingual of an axis between c and p3. The distance between c and p3 is short. A short c–p3 length is also seen in P. marshi and P. aeluroides , but contrasts with the long c–p3 length seen in P. validus . The p3 of F:AM 61812 has a fractured crown, but the anterior and posterior cingular cusps are present. The anterior cingular cusp is minute, which differs from the more prominent anterior cusp described in P. cuspidatus but agrees with other species of Pseudaelurus . The large two­rooted p4 alveolus has a posterior root that is much larg­ er than the anterior. Three mental foramina are present on the lateral surface. The largest and most anterior of these is at the level of the p2 alveolus.

The m1 is well preserved, missing only a sliver of the anterior border of the paraconid. The carnassial notch is deep, narrow, and open to a level that is even with the reduced talonid. The protoconid is much taller than the paraconid, which agrees with the condition in P. cuspidatus . This degree of disparity in the height of paraconid and protoconid is not seen in other North American species. On the posterior margin of the paraconid is a reduced but distinct metaconid, aligned with the axis of the protoconid (fig. 22). The reduced metaconid is not lingually positioned as in P. cuspidatus , and it blends into a reduced but prominent talonid.

DESCRIPTION AND COMPARISONS OF RE­ FERRED MATERIAL: The greater height of m1 protoconid described in the type specimen (F:AM 61812) is seen also in F:AM 61816 (fig. 25) and F:AM 61817 (fig. 26). All of the m1s have a prominent metaconid and distinct talonid. The presence of a metaconid in other North American species of Pseudaelurus is variable. F:AM 61813, the maxillary fragment, is the only upper dentition known for the species (fig. 27). P3 has a prominent posterior accessory cusp as well as a basal cingular cusp. On the labial side of P4 there is a small accessory cusp at the base of the parastyle. This morphology of P3 and P4 agrees with P. validus . The P4 of F:AM 61813 has a prominent protocone (fig. 28). The slenderness and the angle of the P4 protocone are similar to the P 4 in the type skull of Proailurus lemanensis (MNHN1903–20) (fig. 29). The protocone lies at a more obtuse angle anterolingually than is seen in P. intrepidus and P. marshi . This less acute angle formed by the protocone of P4 compares well with P. validus . M1 of F:AM 61813 is fragmented. Only the lingual half of the tooth remains. However, it is obvious that this M1 was multicusped. This agrees with the condition in P. validus , in contrast to the vestigial M1 seen in modern felids.

DISCUSSION: Material referred to P. skinneri is restricted to lower and upper jaw specimens from late Hemingfordian localities of North America. Without cranial and postcranial information, it is difficult to hy­ pothesize the relationship of P. skinneri with other felids. One possibility is that it is most closely related to the other similar­sized species found on other continents. Fossils of P. lorteti of Europe are similar in size and morphology and are temporally equivalent to P. skinneri . This is not unlike the situation seen today with Lynx lynx of Europe and Lynx canadensis of North America. In Asia, Pseudaelurus cuspidatus , P. guangheensis , and P. lorteti are all similar in size to P. skinneri and all have been reported from middle Mio­ cene localities. Conversely, there is no reason to expect the diversity of early felids in North America to reflect the situation in Europe or Asia. P. skinneri along with P. validus are among the earliest felids to arrive in North America. It is possible that P. skinneri is more closely related to P. validus than to Eurasian species. Perhaps P. skinneri and P. validus represent part of an early North American radiation of felids. Without additional material (e.g., basicrania and postcrania) however, it will be difficult to determine the relationship of P. skinneri to other Miocene felids.