Pseudaelurus intrepidus Leidy, 1858

ROTHWELL, TOM, 2003, Phylogenetic Systematics of North American Pseudaelurus (Carnivora: Felidae), American Museum Novitates 3403, pp. 1-64 : 27-32

Pseudaelurus intrepidus Leidy, 1858

HOLOTYPE: USNM 124 ( AMNH cast 10396), left ramus with i3, alveolus p2, p3– m1 from the Valentine Sands, Bed F, ‘‘ Loup Fork’ ’, Valentine Formation (late Barstovian ( Webb, 1969), Cherry County, Nebraska (fig. 5).

REFERRED SPECIMENS: Lower Snake Creek Fauna, Olcott Formation (early Barstovian), Sioux and Dawes counties, Nebraska: YPM PU 12081, right partial ramus with broken c, alveolus p2, p3–broken m1, Sinclair Draw; AMNH 17212, right partial ramus with broken c alveolus, alveoli of p2 and p3, p4–m1, Sinclair Draw; F:AM 61806, left ramus with broken c, p2 alveolus, p3–m1, Humbug Quarry; F:AM 61804, right ramus with alveolus of I3, broken canine, and p2–m1, Quarry 2; F:AM 61805, right ramus with alveolus of canine and p3–m1, Quarry 2; F: AM 61831, right ramus with alveolus of canine, alveolus of p2, broken p3, and p4–m1, Echo Quarry; F:AM 61564, left partial ramus with p3–broken m1, Version Quarry; AMNH 18271, with broken c, alveolus of p2, broken p3–m1, East Surface Quarry.

Trinity River Local Fauna, Fleming Formation (early Barstovian), San Jacinto County, Texas: AMNH 18271, right partial ramus with alveolus of c, alveolus of p2–p4 and m1, pit no. 1.

Tonopah Local Fauna, Siebert Formation (early Barstovian), San Antonio Mountains, Nye County, Nevada: LACM ( CIT) 791, partially restored skull with upper dentition and basicranium, locality 172; LACM ( CIT) 1233, maxillary fragment with C–M1, and right ramus with i3–c, p2–m1, locality 172; LACM ( CIT) 772, left partial ramus with p3–m1, locality 172; LACM ( CIT) 1234, left partial ramus with p3–m1, locality 172.

Green Hills Fauna (early Barstovian), Barstow Formation, San Bernardino County, California: F:AM 61923, right partial ramus with broken c, p2–p3, broken p4, and m1, Upper Steepside Quarry; F:AM 27331, right crushed ramus with c, p2–m1 and left ramus with broken c, p2–m1, ‘‘Green Hills, Box 72, 1926’’; F:AM 27327, left partial ramus with c, p2–m1, ‘‘Green Hills, Box 59, 1925’’.

Pawnee Creek Formation (early Barstovi­ an), Big Springs Pit, Weld County, Colorado: F:AM 61842, left partial ramus with alveolus p3, p4–m1 .

Second Division Fauna, Barstow Formation (early Barstovian), San Bernardino County, California: F:AM 61933, left and right rami with i3–c, p2–m1, Mayday Quarry .

First Division Fauna, Barstow Formation (late Barstovian), San Bernardino County, California: F:AM 61910, partial skeleton with left and right rami with i3, c, p2–m1, right humerus, radius, tibia, and partial femur, left articulated forearm (radius, ulna, and manus) with prepared metapodials, left tibia, left partial humerus and femur, partial axis, metatarsal fragments, unprepared vertebrae, and partial scapulae, 6 ft under New Year Quarry; SBCM L1816–5224 , crushed skull with broken I1–M1, and left and right rami with broken I–c, p2–m1, Robbins Quarry .

Valentine Formation (late Barstovian), Elliot Place, Brown County, Nebraska: AMNH 25209, right partial ramus with alveoli of i1– i3, c, alveolus of p2, p3–m1;

Valentine Formation (late Barstovian), Cherry County, Nebraska: ANSP 11297, right ramus with i2, broken i3 and c, alveolus of p2, p3–m1 (paratype), ‘‘ Valentine Sands, Bed F, Loup Fork’ ’ ( Webb, 1969) .

DISTRIBUTION: Early Barstovian of Texas, Colorado, and Nevada, early and late Barstovian of Nebraska and California.

DIAGNOSIS: Differs from similar­sized species of Pseudaelurus by the c–p3 length and coronoid process morphology. P. intrepidus has an m1 length range of 15–20 mm, overlapping only with P. validus and P. marshi in North America and P. quadridentatus in Europe. P. intrepidus can be differentiated from P. validus by its shorter c–p3 length and by its slender and sloping coronoid process. P. intrepidus can be differentiated from P. marshi by its longer c–p3 length and by a taller and wider dentary. P. intrepidus can be differentiated from P. quadridentatus by its longer c–p3 length, and by having an m1 with larger talonid and a better developed, larger metaconid.

DESCRIPTION AND COMPARISONS: In Leidy’s (1858) original description, he described the type lower jaw ramus (USMN 124, AMNH 10396) (fig. 5) as being ‘‘intermediate in size to the Panther ( Felis concolor ) and the Lynx ( Felix canadensis ).’’ This specimen is longer, wider, and deeper than a modern lynx ( Lynx canadensis ). Its dentition is closer in size to that of the puma ( Felis concolor ). The dentary is wide and deep below the tooth row. The lower dentition of P. intrepidus is similar to that of other species within the genus. The c is flattened medially and has a distinct posterior trenchant edge. The p2 alveolus was single­rooted and was positioned midway in the diastema between c and p3 (fig. 5). The distance between c and p3 is long, measuring 76% of the m1 length. This is in contrast to P. marshi , which has a shorter c– p3 length that measures 54% of its m1 length in the type specimen, and P. validus , which has a c–p3 length that exceeds the length of m1. The slender coronoid process extends posterodorsally from a deep masseteric fossa. This contrasts with the larger, wider, and more erect coronoid process in P. validus , but is indistinguishable from P. marshi specimens.

The earliest specimens of P. intrepidus are seven rami from various early Barstovian localities of the Lower Snake Creek Fauna of Nebraska. F:AM 61804 (fig. 30) is a right ramus from East Surface Quarry in Sioux County from this early group. These early Barstovian P. intrepidus differ from the late Barstovian holotype in lacking the pronounced chin or thickening of the dentary below the canine. Matthew’s ramus of P. intrepidus sinclairi (AMNH 17212) (fig. 31) is another early Barstovian lower jaw of Pseudaelurus intrepidus . In spite of its historical status and ‘‘variety’’ designation, it does not differ appreciably from the type specimen.

I am unable to differentiate P. intrepidus and P. marshi material that is unaccompanied by a lower jaw. Therefore, diagnosed upper dentitions of P. intrepidus are not common. I am aware of only three. The earliest is from the Tonopah locality reported by Stock (1934): a maxillary fragment with an associated partial ramus (LACM CIT 1233) (fig. 32). P1 and P2 are both single­rooted. The P4 has a prominent protocone that projects anterolingually. As in P. validus and P. skinneri , the anterior surface of P4 has a prominent parastyle with a small but distinct accessory cusp. The P4 morphology of P. intrepidus is better seen in F:AM 61910 (fig. 33), but this crushed specimen lacks M1. The third Pseudaelurus intrepidus specimen with upper dentition is SBCM L1816–5224, a late Barstovian partial skull from the Barstow Formation. It does not differ from the other two P. intrepidus skulls.

In addition to the maxillary fragment, Stock (1934) described a partially restored skull (LACM (CIT) 791) (fig. 34). This was the first skull of the genus Pseudaelurus described. It was also the only Pseudaelurus skull described until the description of the Nambé felid, P. validus ( Rothwell, 2001) . Other felid skulls in the Frick­AMNH collection have been featured in a basicranial study ( Hunt, 1998), but there was no attempt at assigning genera and species. There is considerable plaster repair and replacement in the area of hard palate, zygomatic arches, and frontal bones of LACM (CIT) 791. There is no accompanying lower jaw. The upper dentition of the Tonopah skull (LACM (CIT) 791) agrees with the Tonopah maxillary fragment (LACM (CIT) 1233) in size and morphology. The occlusal surface of M1 is contiguous with the P4 carnassial blade (fig. 35). This characteristic of the upper carnassial apparatus in specimens of P. intrepidus agrees with the P. validus skulls.

The paroccipital process of the Tonopah skull, assigned to P. intrepidus , is cupped about the posterior surface of the caudal entotympanic, pointing caudoventrally away from the posterior surface of the bulla as a distinct process. The anterior portion of the sagittal crest has been estimated in plaster by a preparator, but the caudal portion and the nuchal crest resemble P. validus . The alisphenoid canal can be seen on both sides of the Tonopah skull. The size and location of these foramina do not differ from those seen in other skulls assigned to Pseudaelurus . The other two skulls that I assign to P. intrepidus are F:AM 61910 and SBCM L1816–5224. The size, dentition, and cranial foramina of

TABLE 1 Greatest Length Measurements (mm) of Components of F:AM 61910 Skeleton, Referred to Pseudaelurus intrepidus (length of metatarsal 3 has been estimated)

these crushed specimens do not differ from the skull described by Stock (1934).

Postcranial information on Pseudaelurus intrepidus is provided by F:AM 61910. The postcranial elements do not differ morphologically from F:AM 62128, the partial skeleton from the Nambé Member in New Mexico assigned to P. validus ( Rothwell, 2001) . However, the metacarpal measurements of the P. intrepidus skeleton are relatively longer than those of P. validus specimen (table 1). The occurrence of longer metacarpals is similar to modern felids and differs from the shorter metacarpal form seen in Proailurus lemanensis and P. validus (figs. 36–38).

DISCUSSION: Pseudaelurus intrepidus is the only species of Pseudaelurus in North America that has been described in the literature more than once ( Sinclair, 1915; Matthew, 1918; Stock, 1934). Lower jaw specimens of P. intrepidus are abundant in the Frick­ AMNH collection and come from Barstovian localities of Texas, Colorado, Nevada, Nebraska and California. I studied 22 lower jaws that I assigned to P. intrepidus . Only three of these lower jaws are associated with other material (e.g., cranial, maxillary, postcranial).

The dentition of P. intrepidus does not differ significantly from other North American species of Pseudaelurus . However, P. intrepidus is among the earliest felids to display the derived condition of a sloping and slen­ der vertical ramus of the lower jaw. The Lower Snake Creek Fauna, in the early Barstovian of North America, has felids with the primitive coronoid process ( P. validus ) as well as three species with vertical rami that display the derived condition ( P. intrepidus , P. marshi and P. stouti ). In the late Barstovian, all felids studied have the derived sloping coronoid process seen today in modern felids (fig. 10).

The prominent chin seen in late Barstovian specimens of P. intrepidus leads to speculation that this species could be ancestral to one or more of the many machairodont felid forms seen in the late Miocene. This prominent chin, seen also in late Barstovian P. marshi , is a thickening of the dentary on the ventral surface below the lower canines. The ventral thickening of the dentary is associated with an elongation of the mandibular symphysis. It is well demonstrated in the type specimens of P. intrepidus and P. marshi (figs. 5, 6). Early specimens of these two species lack these characters (fig. 30). Numerous authors have included early specimens of machairodont felids in the genus Pseudaelurus ( Andrews, 1914; MacDonald, 1948b, 1948a; Ginsburg, 1978). Indeed, Pseudaelurus has been designated as a likely ancestor of the machairodont North American felid Nimravides (fig. 8) ( Baskin, 1981; de Beaumont, 1990).

None of the three P. intrepidus skulls (LACM (CIT) 791, SBCM L1816–5224, F: AM 61910) is well preserved. Cranial and basicranial information on P. intrepidus is limited. However, the postcranium of P. intrepidus (F:AM 61910) does allow comparison with other taxa. Although conclusions made from one skeleton must be provisional, it appears that late Barstovian P. intrepidus had different proportions of its limb bones. In figure 36, I have contrasted the P. intrepidus data with the earlier P. validus postcranium. The y­axis or standard specimen is the Proailurus lemanensis skeleton described by Filhol (1888). The P. validus data are reasonably vertical and therefore similar to P. lemanensis . Thus, their limb proportions are comparable. The P. intrepidus skeleton (F: AM 61910) is different. In the front limb, the metacarpal bone is relatively larger. In the hind limb, the femur has decreased in relative size, while the tibia has increased. This form compares favorably with modern felid skeletons. In figure 37, data from L. issiodorensis ( Kurtén, 1978) , the suspected ancestor of Lynx lynx and Lynx canadensis ( Werdelin, 1981) , is added for comparison. In figure 38, modern taxa are also included for comparison. P. intrepidus shares the modern skeletal form of greater relative metacarpal length in the front limb and increased tibial length in the hind limb.