Pseudaelurus skinneri, ROTHWELL, 2003

ROTHWELL, TOM, 2003, Phylogenetic Systematics of North American Pseudaelurus (Carnivora: Felidae), American Museum Novitates 3403, pp. 1-64 : 13-20

lent P. skinneri .

F:AM 61829 (fig. 11) has the large distance between c and p3 that is distinctive of P. validus . In every observed lower jaw of P. validus , except for the crushed and restored holotype, the c–p3 distance exceeds the length of m1. Lower jaws assigned to P. intrepidus have c–p3 length ranging from 68% to 98% of the m1 measurement. In P. marshi , the type lower jaw (YPM 12865) has a c–p3 length 54% of the m1 length, and in the paratype (YPM 12815) it is 66%. In my study of modern felids, both male and female lions ( Panthera leo ) have an average c–p3 length that measured 110% of the m1 length (see tables 4, 5), a proportion similar to P. validus . In the puma, Felis concolor , the average c–p3 length was 66% of the m1 length in females, and 69% in males, corresponding more to the condition in P. intrepidus and P. marshi .

The lower dentition of P. validus is similar to that in other species within the genus. None of the specimens has p1. The p2 is usually indicated by a single­rooted alveolus positioned medial of the line of tooth row, as in the type. The left lower jaw of F:AM 61829 (fig. 11) has a two­rooted p2. This is the earliest example of a two­rooted p 2 in North America. The number of roots of p2 varied in early European felid specimens ( Dehm, 1950). A two­rooted p2 is routinely seen in the European taxon Proailurus ( Filhol, 1888; Peigne´, 1999), generally accepted as the earliest member of Felidae ( Hunt, 1989) .

The height of p 3 in P. validus is consistently lower than p4. The primitive condition of equal­sized p3 and p4 can be seen in the European aeluroid taxa Stenogale and Haplogale (Peigne´, 1999). The derived condition of p3 smaller than p4 is present in Proailurus , Pseudaelurus , and modern felids. The p4 of P. validus has a large posterior accessory cusp. The m1 metaconid is more reduced than in other early and middle Miocene felids. In seven lower jaw specimens assigned to P. validus that have m1 present, four have a greatly reduced (for Pseudaelurus ) metaconid (fig. 12) and three have no detectable metaconid. The derived condition of a reduced metaconid contrasts with the m1

of Pseudaelurus skinneri , n. sp. which has a very distinct metaconid accompanied by an abridged talonid. The reduced metaconid morphology also differs from the later P. intrepidus , P. marshi and P. stouti , species whose m1 have a varying incidence of a more distinct metaconid.

The upper dentition of P. validus has been described for the type specimen, but is better preserved in many of the referred specimens (figs. 13–15). P3 of P. validus is large, with a primary cusp that is approximately the same size as the paracone of P4 (fig. 15). The posterior accessory cusp of P3 is also large and distinct and is approximately the same height and size as the parastyle of P4. Posterolateral to the posterior accessory cusp of P3 is a prominent cingular cusp. This cingular cusp is at the same level and of the same height and size as the anterior accessory cusp of the adjacent P4. These corresponding cusps of P3 and P4 can be seen in the lateral view of figure 15. The P4 of P. validus is wide, not compressed mediolaterally, as in modern felids. The P4 has a prominent protocone that projects anterolingually from the lingual surface of the paracone of P4 (fig. 14). In all referred specimens that have M1, the parastyle blade is contiguous with the metastyle blade of P4. This morphology elongates the upper carnassial blade in this species.

The ventral aspect of the skull of F:AM 61835 is in excellent state of preservation (fig. 16). Portions of the basicranium of this specimen have been described and illustrated previously ( Neff, 1983; Hunt, 1998). The ectotympanic is thick and massive. The anterior crus have two components. There is a large

Proailurus lemanensis (late Oligocene, early Miocene), drawing from Filhol (1888); B, Pseudaelurus validus (F:AM 61829) (early Miocene); C, Pseudaelurus skinneri (F:AM 61812) (early Miocene); D, Pseudaelurus intrepidus (USNM 124) (middle Miocene), drawing from Leidy (1869); E, Felis concolor (AMNH 11082), recent, drawing from Matthew (1910). The coronoid process is short and erect in Proailurus , still somewhat erect in P. validus and P. skinneri , but slender and sloping in P. intrepidus and modern felids.

anterolateral attachment to the squamosal and a thick and wide medial articulation with the lateral margins of the basioccipital and basisphenoid. The suture between the basioccipital and basisphenoid cannot be identified. The left auditory bulla has been dis­ sected (fig. 17). The course of the septum bullae can be seen to run diagonally, along the posterior wall of the ectotympanic, across the crest of the promontorium, from a point just medial to the vagina processus hyoideus, anteromedially to a position considerably posterior to the anteromedial process of the auditory bulla. The course of the septum bullae demonstrates the level of anterior expansion of the caudal entotympanic in P. validus . The caudal entotympanic has advanced anteriorly to a level slightly posterior to the most anterior limit of the ectotympanic chamber. The caudal entotympanic chamber terminates posterior to the anteromedial process. This morphology is similar to the condition seen in Proailurus lemanensis ( Hunt, 1998) , but contrasts with modern felids whose thin­walled caudal entotympanic has advanced farther anteriorly. Posteriorly, the caudal entotympanic has invaded and emarginated the paroccipital process to a degree seen only in modern felids. For a more indepth analysis of the structures of the auditory region of this specimen, see Hunt (1998: 46).

On the ventral surface of the basioccipital of F:AM 61835, between the two bullae, are two round rugose areas of attachment for the paired rectus capitus ventralis muscles (fig. 16). These two muscle insertion areas are much larger and more expanded than on skulls of other species of Pseudaelurus . This increased area of attachment is seen also in F:AM 61834 skull (fig. 18). There is no evidence of a postglenoid foramen in either F: AM 61834 or F:AM 61835. The postglenoid foramen is present in the type skull of the earlier European felid Proailurus lemanensis (MNHN 1903–20). In the skulls of four species of extant felid that I studied ( Panthera leo , Felis concolor , Lynx canadensis , Lynx rufus ), the postglenoid foramen was variably present, although minute.

The foramen ovale in F:AM 61834 and F: AM 61835 is located at the level of the anteroventrally facing glenoid fossa (figs. 19, 20). This agrees with the location of this foramen in the type specimen (F: AM 62128 ) and does not differ from modern species. The three skulls assigned to P. validus (F:AM 61834, 61835, 62128) have distinct anterior and posterior alisphenoid foramina, with the anterior alisphenoid foramen positioned anterodorsally to the posterior alisphenoid foramen. Careful examination of F:AM 61834 and F:AM 61835 reveals a patent foramen rotundum within the alisphenoid canal. The foramen rotundum opens in the general direction of the anterior alisphenoid foramen. This contrasts with the condition in modern felid skulls, in which the alisphenoid canal is absent. In extant felid species, the foramen ovale retains its position medial to the glenoid fossa, while the foramen rotundum is positioned farther anteriorly .

In both F:AM 61834 and F:AM 61835, a well­developed external pterygoid fossa can be seen immediately ventral to the alisphenoid canal. Both of these skulls also have well­preserved palatine and pterygoid bones. The paired vertical plates of the palatine bones are parallel to each other when viewed from the ventral aspect. However, the paired pterygoid bones are not parallel, but rather reflect medially toward each other posteriorly, thus giving an oval shape to the area between the corresponding plates.

Some extremely well­preserved postcranial bones from the early Barstovian Echo Quarry are referred to P. validus (F:AM 61828 and F:AM 61828­A). However, they do not differ in size or morphology from the type specimen (see Rothwell, 2001).

DISCUSSION: P. validus has a dentition that is for the most part primitive for felids, but some states are derived relative to Proailurus . P1, P2, and p2 of P. validus are vestigial and peglike. These teeth do not occlude. There is a great difference in size between the upper and lower second and third premolars. The third premolars (p3, P3) are robust and possess accessory cusps that assist in mastication. The well­preserved F:AM 61834 skull and its associated lower jaws (F: AM 61829) (figs. 11, 18) provide insight into early felid occlusion. The carnassial activity is centered at the carnassial notches of P4 and m1, as in all Carnivora . The shear activity of F:AM 61834 extends anteriorly to the anterior surface of P3, which occludes with the posterior surface of p3. This morphology is identical to the condition in modern felids. Posteriorly, the upper carnassial activity continues to the parastyle blade of M1 (M1 missing in F:AM 61834 skull, present in F: AM 61835 skull), which occludes with the reduced metaconid and talonid of m1. Mod­ ern felids, in which M1 is vestigial and the metaconid and talonid of m1 are absent, have lost the occlusal ability of M1. The erect coronoid process of P. validus agrees with the condition in the smaller, but temporally equivalent species, P. skinneri . Outgroup comparison to earlier fossil aeluroids such as Proailurus , Stenogale , Haplogale , and Stenoplesictis establishes this erect morphology of the ascending ramus as a plesiomorphic condition for the family Felidae .

In both F:AM 61834 and F:AM 61835 the alisphenoid foramina are nearly perfectly preserved. Both skulls show evidence of the alisphenoid canal, foramen rotundum, and foramen ovale (figs. 19, 20). The primitive eutherian condition for these foramina ( Novacek, 1986; Rougier, Wible et al. 1992) and their role in circulation ( Davis and Story, 1943) have been previously described and illustrated. In a hypothetical primitive aeluroid, the mandibular branch of cranial nerve V exits the cranium via the foramen ovale. Entering the foramen ovale from outside of the skull is a branch of the carotid circulation via the maxillary artery. This branch of the maxillary artery enters the cranium and forms an anastomosis with the internal carotid circulation ( Davis and Story, 1943). In this hypothetical aeluroid, the maxillary branch of cranial nerve V exits the cranial cavity via the neomorph foramen rotundum and enters the alisphenoid canal. The maxillary branch of the trigeminal nerve (V) then proceeds anteriorly in the alisphenoid canal and exits the skull via the anterior alisphenoid foramen. As it leaves the anterior alisphenoid foramen, the nerve branch is accompanied by the maxillary artery, which has just traversed the alisphenoid canal after entering the posterior alisphenoid foramen. This is the condition in Pseudaelurus validus . On the floor of the cranial cavity in F: AM 61835 (fig. 21) are seen three separate grooves associated with the three branches of the trigeminal nerve (ophthalmic, maxillary, and mandibular) as they exit the braincase via separate foramina.

Modern felids have greatly increased the degree of anastomosis of the external and internal carotid circulations over the primitive condition, decreased the role and size of the internal carotid artery, and incorporated the maxillary artery into a complicated rete externum. However, in the area of the alisphenoid foramina, modern felids differ from P. validus only by lacking external evidence of passage of the maxillary artery—the alisphenoid canal. The primitive condition of an ali­ sphenoid canal present in Pseudaelurus validus , and the derived state of absence of alisphenoid canal in Felis , supports the hypothesis that loss of the alisphenoid canal developed in parallel in the family Hyaenidae ( Werdelin, 1996) . Loss of the alisphenoid canal is another example of a character that should not be considered a synapomorphy for these two aeluroid families, as previously suggested ( Wyss and Flynn, 1993).

In the auditory region of Pseudaelurus validus , the caudal entotympanic chamber has expanded slightly beyond that seen in Proailurus (see Hunt, 1998: 35). This anterior expansion of the caudal entotympanic can be monitored by the emargination of the adjacent basioccipital ( Hunt, 1998). Although the emarginated basioccipital ridge in P. validus and Proailurus lemanensis is similar, a greater percentage of the caudal entotympanic lies anterior to the petrosal in P. validus (fig. 17). In P. validus , the anteromedial process is formed by robust medial crus of the ectotympanic. This area of the basicranium in P. lemanensis is unknown. In modern felids, the caudal entotympanic has advanced farther anteriorly, invading the medial crus of the ectotympanic and leaving the anteromedial process to be formed mostly of thin­walled caudal entotympanic.