Skull

The skull (figs. 2a, 2b) has been crushed, giving it a low and wide appearance. This compromises the integrity of some skull measurements, especially those of height and width. However, the upper dentition survived, and can be associated with the lower teeth for only the second time in this genus. The premaxillary bones possess a pair of fragmented I3, the I1–2 having been lost. A short and smooth diastema separates I3 from C. The left C is separated from the skull, revealing a large, cavernous alveolus. The right C root is in situ; however its crown is fractured and missing. These two C are more elliptical than round in cross-section and lack any longitudinal grooves. Posterior to the alveolus for the left C are a preserved P1 and an alveolus for P2, both single-rooted. This agrees with the presence of these teeth in the skull described by Stock (1934) from Tonopah, although the presence of P1 was interpreted by Stock as being “a rather unusual feature”.

The lengths of P3 and P4 in P. validus agree with the Tonopah skull but are smaller than the P. quadridentatus type. These two teeth are aligned parallel to the maxillary axis and do not exhibit any overlap, obliqueness, or crowding as seen in some extant species (Salles, 1992). The left P3 is wider and more robust when compared to P3 in the P. lemanensis type skull (MNHN1903–20). On the right P4 (fig. 2b) can be seen a prominent protocone that projects in an anterolingual direction. The morphology of P4 in F:AM 62128 resembles the P4 in the P. quadridentatus maxillary fragment from la Grive-Saint-Alban (Isère) (cast = AMNH 103396) described by Gaillard (1899). In the P. lemanensis type specimen, the protocone of P4 is at a slightly more obtuse angle to the lingual surface of P4. In modern felids, the protocone is closer to the lingual surface of the tooth, resulting in a narrower, compressed P4. The P4 of F:AM 62128 has a parastyle on the anterior surface which does not differ from the condition in P. lemanensis other species of Pseudaelurus or modern felids.

Both M1 are present with two roots. The M1 are compressed in the a-p direction, but are elongate transversely. Individual cusps can be seen on the left M1. The buccal end of this tooth is formed by the parastyle wing. The nearly conjoined paracone and metacone are midway along the occlusal surface. The lingual margin of M1 is formed by a distinct protocone. The parastyle of F:AM 626128 M1 is as tall as the caudal surface of the metastyle blade of P4 and appears to extend the carnassial blade. The left M1 of F:AM 62128 compares favorably with the M1 in the P. lemanensis skull (MNHN1903–20), but is in sharp contrast to the rudimentary M1 of modern cats.

The skull has a high, thin sagittal crest which is joined by equally large nuchal crests that unite at the occiput to form a protuberance that projects to a point caudal to the level of the occipital condyles. This area of the skull is very similar to the type skull of P. lemanensis (MNHN1903–20) from the early Miocene of France. The basicranial anatomy of F:AM 62128 is somewhat distorted, but much information endures (figs. 2b, 3). On the right side of the skull, much of the ossified bulla is lost, but the close approximation of the mastoid and paroccipital process to the bulla can be appreciated. The paroccipital process displays a concavity on its anterior surface where it cradled the posterior surface of the tympanic bulla in typical aeluroid fashion (Cope, 1880; Hunt, 1987, 1989, 1998; Werdelin, 1996; Wyss and Flynn, 1993). Medially, the ridge formed by the caudal entotympanic indenting the basioccipital bone can be seen (fig. 3). On the lateral margins of the right bulla, just proximal to the mastoid process, is the external acoustic meatus surrounded by most of the ectotympanic. This evidence of the anterolateral compartment of the bulla gives a strong signal as to the inflated size of the caudal entotympanic. This is further evidence that this Nambé Pseudaelurus specimen possessed felid characters in the basicranial area (Hunt and Tedford, 1993).

The petrosal bone and its promontorial process are preserved in the tympanic bulla region on the left side (figs. 2b, 3). Although the petrosal has been nudged in a caudal direction by the crushing, facets for its articulation with the ectotympanic can be seen on its ventral surface. The grooving of the anterodorsal roof of the tympanic bulla, formed by the anterior invasion of the caudal entotympanic to the level of the squamosal bone, can also be seen. The hypoglossal foramina are visible bilaterally, within the depression where the posterior lacerate foramina would be.

Lower Jaw

The two rami of the lower jaw were cemented together during early, cursory preparation (fig. 4). The size of this jaw is smaller than Leidy's P. intrepidus type, and is more similar in size to P. marshi (table 1). However, it is obvious that this jaw was reconstructed from multiple fragments, thus compromising its measurements. The mandibles are not slender, as described in Thorpe's P. marshi specimen, but rather display considerable depth below the tooth row. The ventral surface of the lower jaw is slightly convex, but the area immediately below the tooth row is essentially straight. There is no ventral bulge in this location.

Both of the large lower canines are preserved. The inner surface of each is more flattened than the outer surfaces. Their crowns do not possess any grooves. In the space between c and p3 on both rami is an alveolus for p2, located not at the midpoint in the diastema as in Leidy's description (Leidy, 1869), but considerably closer to p3 (fig. 4). This single alveolus is also located medial of the line of the tooth row, a character first described by Thorpe (1922) in the P. marshi type specimen. This medial location of p2 is a consistent feature in the North American specimens, and can be seen in the P. intrepidus and P. intrepidus sinclairi types (Matthew, 1918; Thorpe, 1922). Although the number of roots of p2 varied in early European specimens (Dehm, 1950), I am unaware of any references, in North America, to a double-rooted p2.

The anterior mental foramina are located beneath the posterior portion of the c-p3 diastema, and are best seen on the left ramus of this jaw (fig. 4). The left posterior mental foramen is underneath the posterior root of the third lower premolar. This location agrees well with Stock's (1934) description of the Tonopah specimens that he assigned to P. intrepidus and is in slight contrast to the more anterior location in the P. marshi specimen (Thorpe, 1922). The coronoid process is wider and more erect than in the Leidy or Marsh types and is much taller than in P. lemanensis There is no terminal “hook” in the coronoid process as is seen in modern felids. The deep masseteric fossa of F:AM 62128 extends anteriorly to a point just below the talonid of m1. The F:AM 62128 condyle has a mediolateral articular surface that is 20% longer than the Leidy type, and sits higher by an equal amount above the angular process.

The p3 and p4 are damaged by crushing. However, their size is recoverable (table 1). The posterior accessory cusps of the left p3 and both p4 can be seen on the posterior surface of the primary cusps. These posterior accessory cusps are separate from a well-defined posterior cingulum. This condition of a conspicuous posterior accessory cusp on p3 and p4 is present in specimens of Proailurus lemanensis and persists, with little change, in modern felids. The left m1 is well preserved and demonstrates a much-reduced metaconid that blends smoothly into an abridged talonid. The protoconid is taller than the paraconid and the carnassial notch is open and deep. This description of the carnassial would fit the diagnosis of any of the previously described large Pseudaelurus species of North America: P. intrepidus, P. marshi or Matthew's sinclairi variety of P. intrepidus

Because of the predominance of lower jaw material in the fossil felid literature, this portion of the skeleton must be given special consideration with respect to diagnosis and species referrals. Most species within the genus Pseudaelurus are represented only by lower jaws. A recent study utilizing bivariate analysis (Glass and Martin, 1978) concluded that mandibular dentition is useful in differentiating extant felid species. However, to rely on lower jaw material for purposes of specific diagnosis is at present problematic. In table 1 and in the log-ratio diagram (Simpson, 1941) of figure 5, the lower jaw of the Nambé skeleton is compared with four North American type specimens.

Humerus

In the first description of a postcranial Pseudaelurus specimen, Claude Gaillard (1899) compared a P. turnauensis right humerus from La Grive-Saint-Alban with that of a domestic cat (Felis catus) and of a lynx (Lynx lynx). The Pseudaelurus humeri from the Nambé Member are 50% larger than the specimen from France. The shaft of the F:AM 6128 right humerus (fig. 6) is thinner when viewed from the anterior or posterior perspective. Its lateral and medial surfaces appear broad and flat. The proximal end of each humerus consists of a convex arthral surface that is visible only from the posterior view. This articular surface blends into a deep bicipital groove between greater and lesser tubercles of equal height. The greater tubercle continues down the anterior surface of the shaft of the humerus as a sharp, but low, deltoid ridge, very typical of a cursorial carnivore (Ginsburg, 1961a; Wang, 1993). In the dog, this ridge is more exaggerated, and is better termed the deltoid tuberosity. In the domestic cat, this deltoid ridge blends into the humeral shaft by midpoint. In this specimen, however, the deltoid ridge extends well into the distal half of the humerus. This agrees with Ginsburg's description of this character in the P. quadridentatus humerus from Sansan. On the lateral surface of the proximal end of the right humerus, the pectoral ridge extends down from the posterior surface of the greater tubercle (fig. 6).

Modern felid humeri are most cylindrical just distal to the midpoint of the diaphysis, and this is true of F:AM 62128. From this midpoint in the humeral diaphysis, the supracondyloid ridge extends down the lateral margin of the shaft to the point of the lateral epicondyle. This feature is large in this specimen, forming a shelf that curls in the anterior direction. This shelf forms a ridge with a cupped appearance when viewed from the anterior perspective. Forming the medial edge of this distal end of the bone is the medial condyloid ridge. The supracondlyoid foramen is located here. This oval shaped foramen, which carries the brachial artery and the median nerve in Felidae, is somewhat smaller in this specimen when compared to similar sized modern specimens. This is due to the crushing. In other, better preserved Pseudaelurus sp. humeri specimens in the Frick-AMNH collection, these foramina agree in size and shape with modern specimens such as Panthera pardus or Felis concolor

The distal end of the P. validus humeri, while extremely similar to modern felids, possesses certain characters that resemble the humerus of Proailurus Differing in the proportions of the medial epicondyle, depth of olecranon fossa, and the distally projecting medial margin of the trochlea, the Pseudaelurus humerus maintains a position intermediate between Proailurus and modern felids. The two P. validus humeri possess large, bulbous, and convoluted medial epicondyles, deep olecranon fossae, and robust medial margins of the trochleae. This morphology agrees well with Ginsburg's (1961b) description of Pseudaelurus quadridentatus which he stated was closer morphologically to Proailurus than to modern felids. The large and rough-surfaced medial epicondyles, typical of animals that climb (or dig) (Taylor, 1976; Heinrich and Rose, 1997) are in contrast to the smaller and smoother epicondyles in modern felids. This combination of enlarged medial epicondyle and deep olecranon fossa suggests that this species was a reasonably cursorial cat (Wang, 1993). The capitulum on the humeral trochlea is convex and faces primarily in an anterior direction. Medially, the arthral surface becomes concave and terminates in a distally projecting, robust trochlea. Just proximal to these structures, on the anterior surface is the radial fossa adjacent to the more lateral and slightly smaller ulnar fossa.

Radius

The right radius (fig. 7) has a proximal surface that is oval in shape. The bone immediately narrows into a brief neck area just prior to the bicipital tuberosity that lies on the posteromedial surface. The shaft is roughly cylindrical and is convex in the lateral and cranial direction. All of these characters agree with modern Felidae. The radius increases in diameter distally. Unless this is due to crushing, it agrees with the description of Proailurus (Ginsburg, 1961b), and may establish a plesiomorphic character state for felid radii.

Ulna

The right and left ulnae of F:AM 62128 are complete. The right (fig. 7) was selected for description. There is considerable width or surface area of the trochlear notch, more so than in extant felids. This joint surface is interrupted only by the laterally excavated radial notch that accepts the head of the radius. This laterally positioned radial notch has been shown to be a consistent character within modern felids (Gonyea, 1978), contrasting with the more cranially located notch in canids and hyaenids. This ulna has a maximum width just below the olecranon fossa and tapers towards its distal termination as the styloid process. Below the olecranon, in the next one-third of the diaphysis, the shaft changes from the two-sided olecranon to a three-surfaced bone. In the final one-third of this bone, the shaft tapers and loses a sense of surfaces.

Carpus

The F:AM 62128 scapholunar proximal surface consists of a dome-shaped convexity for articulation with the distal radius. Its distal surface is extremely complicated, containing facets for articulation with all components of the next row of carpal bones. Most anterior and medial is the facet for articulation with the trapezoid. Moving posteriorly and laterally, there are facets for the trapezium and the magnum, and, on the posterior-most margin of this carpal bone there is the surface for articulation with the unciform. This complicated articulation can be seen in a photograph of a European specimen assigned to P. lorteti (de Beaumont, 1961b, plate 2, #7), and agrees well with modern felids.

The lateral member of the proximal row of carpal bones is the cuneiform. Its lateral surface consists of two equal-sized concave facets for articulation with the ulna and the pisiform. This ulnar articulation is often lacking in modern felids (Merriam and Stock, 1932), but can be clearly seen in this specimen. The pisiform of F:AM 62128 contains a deeper groove on its proximal end than is seen in extant felids, but agrees in this respect with illustrations of Felis atrox and Smilodon californicus (Merriam and Stock, 1932). Otherwise, the cuneiform and the pisiform do not differ from these same elements in modern felids.

In the distal row of carpal bones, most medial, is the trapezium articulating with Mc1. Lateral to the trapezium and articulating with Mc2 is the trapezoid. It is clear that both articulate with the scapholunar proximally, and therefore distribute load to and from the radius. Completing the distal row of carpal bones, the magnum and unciform articulate with the proximal ends of metacarpals 3, 4 and 5.

Metacarpus

The compressed and compact appearance of the articulated metacarpals (fig. 8) coordinates with the hind foot's digitigrade appearance. All five metacarpal bones are present. In this early Miocene specimen, we see metacarpal proportions like those of the living felids: The length decreases from the third to the fifth and the second is shorter than the fourth. The proximal ends of these metacarpals articulate together and with the distal row of carpal bones in a unique and characteristic manner that can be traced through the fossil record into today's modern Felidae (Helbing, 1928; Merriam and Stock, 1932; Ginsburg, 1961a; Wang, 1993).

The first Pseudaelurus Mc1 reported in the literature was from Sansan, France assigned to P. quadridentatus (Ginsburg, 1961b). The F:AM 62128 Mc1 is nearly identical in shape to the drawing on page 143 of that paper. A second P. quadridentatus Mc1, from Los Valles in Spain (Ginsburg et al., 1981), was neither described nor drawn. Both the Nambé Mc1 and the Sansan Mc1 have the morphology of a vestigial metacarpal bone. The distal end of the F:AM 62128 Mc1 has an oblique, medially directed axis with respect to the other four metacarpals (fig. 9). The lateral condyle extends considerably further distally than the medial does. This distorts the distal articular surface, allowing the first phalanx of this digit to articulate in a medial direction. The bone has a blunt and rectangular shape, having lost the length of the other four metacarpals. This shared derived character of vestigial Mc1 persists in all extant Felidae. There is only one accurate reference to a Mc1 in the Proailurus literature (Helbing, 1928). In this paper, Helbing illustrated a Mc1 labeled Proailurus sp that is in the primitive, unreduced state. The Proailurus Mc1, unlike those in the Pseudaelurus specimens, resembles the other four metacarpals. It has a slender, axial diaphysis and a distal articular surface that is parallel to the ground.

The remaining metacarpals, 2 through 5, are robust precursors of their counterparts in modern Felidae (figs. 8, 9). Articulated metacarpals 2, 3, and 4, assigned to the large European species P. quadridentatus were described and illustrated by Ginsburg (1961b). Their proximal articular surfaces are identical to those of the Nambé specimen. F:AM 62128 metacarpals 1, 2, 3 and 5 are accompanied by first phalanges in the prepared right manus (fig. 9). Only two of the second phalanges and one of the third phalanges are present in this front foot. The articulated left manus (fig. 8) contains a more complete set of phalanges. Clearly evident in both mani are lateral concavities in the second phalanges necessary for a retraction and protraction claw mechanism (Bryant et al., 1996). The degree of concavity in the F:AM 62128 second phalanges is not distinguishable from modern felids.

Femur and Patella

Only the distal 39 mm of the left femur and the patella has survived. Although slightly distorted by crushing, the internal condyle can be identified by its greater length. The condyles' articular surfaces fuse anteriorly to form the concave patellar groove. This patellar groove is constrained by heightened edges with distinct margins. The maximum width of the patella occurs just below the upper margin of this sesamoid bone. It is shaped like a teardrop, ending in a blunt distal end. Its dorsal surface is smooth and uniformly convex. However, the ventral surface, which articulates with the femur, consists of a pair of equal-sized concave surfaces that register with the corresponding femoral condyles.

Tibia

The intact left tibia (fig. 10) strongly resembles a modern felid tibia. In the only prior North American description of Pseudaelurus postcranial material, Shotwell and Russell (1963) mentioned “tibia and vertebrae fragments”, but did not describe or illustrate these bones. G. de Beaumont (1961) described tibial material assigned to P. turnauensis and L. Ginsburg (1961b) described a distal tibial fragment assigned to the larger P. quadridentatus Of the distal fragment assigned to the P. quadridentatus specimen from Sansan, Ginsburg stated it “differs not from the size or shape of Felis”

The tibia is the longest bone in the domestic cat, F. catus (Mivart, 1881), but it is exceeded in length by the femur in the Panthera radiation. Both the Proailurus skeleton (Filhol, 1888) and F:AM 62144, a partial Pseudaelurus skeleton in the Frick-AMNH collection from the late Barstovian Rincon Quarry in New Mexico, have femora that exceed their tibiae in length. The tibia of F:AM 62128 has been compressed laterally by crushing. The proximal end displays two large, concave articular condyles that are separated at their cranial and caudal boundaries by depressions for insertion of menisci and collateral ligaments. Dividing these two oval articular surfaces in a sagittal manner is a large intercondylar eminence.

Fibula

Approximately the distal two-thirds of the left fibula and a small distal fragment of the right fibula are present in F:AM 62128. There is no information on the proximal end of this bone. The medial surface of this robust hind limb element is concave, contrasting with the convex lateral surface. The cross section of the shaft of the left fibula is triangular, and terminates in a lateral malleolus with a deep groove for the passage of the peroneus brevis muscle. All of this is in strong accord with modern felids.

Tarsus

The entire right pes of this specimen is articulated (fig. 11). The left rear foot (fig. 12) was disarticulated and prepared. The proximal end of the left calcaneus begins with a shallow groove for the flexor tendons and quickly narrows into a neck much deeper anteroposteriorly than it is wide. The calcaneal facets are distinct and separate. Halfway down the calcaneus length, the bone quickly widens to form the tight s-shaped articulation with the astragalus. This s-shaped articulation, a character of cursoriality (Ginsburg, 1961a) seen in all modern felids, is well displayed in this specimen.

The right astragalus possesses a large and deeply grooved trochlea. There is no evidence of an astragalar foramen. This smooth joint surface appears to offer little restriction or limitation to tibial rotation. It describes a circular arc that extends nearly from the proximal to the distal margin of this tarsal bone. All of these characters of the astragalus demonstrate that P. validus was fully digitigrade (Wang, 1993). There is a short and strong neck, which terminates in a rounded, convex articular surface.

Immediately below and articulating with the astragalus is the navicular bone (fig. 12). Shotwell and Russell (1963) listed a right navicular, but did not provide illustration or description of this Clarendonian specimen from Oregon. The Nambé navicular contains a deeply concave proximal surface for articulation with the astragalus. This articular area occupies most of the proximal surface of this rectangular bone. On the distal surface of the navicular are separate facets for articulation with all three members of the distal row of tarsal bones. This navicular, including its typical caudal projection, strongly resembles its complement in large, extant felids.

Lateral to the navicular is the cuboid, which articulates with the astragalus proximally. The remainder of the third row consists of the three smallest tarsal bones. Superior to Mt3, and therefore the most lateral of the three, is the ectocuneiform. Medial to this is the mesocuneiform, which articulates with the second metatarsal. The third of these, most medial and positioned more caudal to the navicular, is the entocuneiform. All of this tarsal anatomy can be observed in situ in the articulated rear foot (fig. 11) and agrees with modern felids.

Metatarsus and Phalanges

The articulated right pes shows four primary metatarsals tightly compressed side to side, indicating a digitigrade hindfoot (Ginsburg, 1961a; Wang, 1993). These four main metatarsals, numbered 2 through 5, are approximately equal in length. Each bone's diameter varies little throughout its length. However, as in modern felids, the third metatarsal is considerably stouter than the others (fig. 12). The distal ends of the metatarsals widen to form large, prominently displayed arthral surfaces. When viewed from the ventral surface, their articulations with the proximal phalanges are linked by paired sesamoids that are separated by a midline trochlea (fig. 11).

The first metatarsal did not survive in the articulated specimen, but is intact and in place in the prepared left pes (fig. 12). F:AM 62128 Mt1 is plesiomorphic, is not vestigial, and articulates with a proximal phalanx. The Nambé Mt1 has proximal and distal articular surfaces, a slender diaphysis, and an accompanying first phalanx (fig. 13). The proximal end of F:AM 62128 Mt1 is very broad, with an asymmetric arthral surface that articulates with the accompanying entocuneiform. The lateral condyle of the proximal end of this bone is enlarged and extends further proximally. The result of this asymmetry is to direct the digit medially, at an angle from the foot, not parallel with the other metatarsals that point toward the ground. On the ventral surface of the proximal end of Mt1 is a groove for passage of a flexor tendon. Distally the shaft narrows considerably, reaching its minimal diameter in the middle of the diaphysis. The termination of this Mt1 is similar to the four main metatarsals: It enlarges to form an articulation with a proximal phalanx. Ventrally, it displays a central trochlea similar to the four adjacent metatarsals. This distal articular surface is not perpendicular to the bone's axis. The shaft is longer on its lateral margin and this results in a medial deviation of the first digit. This first digit on the rear foot of F:AM 62128 is unlike that in any living member of Felidae. I am unaware of any Mt1 bones in the Pseudaelurus literature. Helbing (1928) published an illustration of a Mt1 (fig. 14) assigned to P. lemanensis which is extremely similar to the F:AM 62128 bone just described. However, the Proailurus Mt1 is more plesiomorphic. It has a more midline sagittal axis than the Pseudaelurus specimen.

The first phalanges of F:AM 62128 do not differ from modern felids. The second phalanges of digits 2 through 4 are roughly half the length of their respective first phalanges. Two of these second phalanges are present in the prepared left pes (fig. 12) while all four can be observed in the articulated right rear foot (fig. 11). The three proximal facets of each second phalanx allow for a strong articulation between the first two phalanges and would appear to minimize torque between the two bones. The second phalanges are asymmetric; their diaphyses are laterally concave. The degree of this concavity is equal to that in the second phalanges of the manus. Both groups of second phalanges of F:AM 62128, those of the manus and those of the pes, resemble those in large, modern felids. The concave lateral surfaces of these second phalanges demonstrate that Pseudaelurus possessed a passive claw retraction and protraction mechanism (Wang, 1993; Bryant et al., 1996). Both the first and second phalanges of metatarsals 2 through 4 possess a groove on their ventral surface, as in extant felids, for passage of the flexor tendon of the claw.

The third phalanges of the pes are large and laterally compressed (fig. 12). On their proximal surfaces is a circular concave area for articulation with the second phalanx. The ventral termination of this joint ends at the plantar process. The beak-like ungual process or bony claw core projects distally, forming the foundation for the keratinous claw. All of this morphology of the third phalanx in P. validus resembles that of large, extant felids. In the third digit of the articulated right pes (fig. 11) can be seen an example of a third phalanx with an intact ungual crest and hood.