Temnocyon ferox Eyerman, 1896

Hunt, Robert M., 2011, Evolution Of Large Carnivores During The Mid-Cenozoic Of North America: The Temnocyonine Radiation (Mammalia, Amphicyonidae), Bulletin of the American Museum of Natural History 2011 (358), pp. 1-153 : 38-41

Temnocyon ferox Eyerman, 1896 Figures 12–14 , 53

Temnocyon ferox Eyerman, 1896: 268–284 , pl. 11, figs. 1–9.

Temnocyon ferox: Wortman and Matthew, 1899: 115–118 , fig. 3.

Temnocyon ferox: Merriam, 1906: 22–23 , 29.

TYPE: PU 10787, as given in Eyerman (1896), a nearly complete articulated skeleton with associated skull and lower jaws, the basicranium badly damaged. Found in the same block with a partial oreodont skeleton, ‘‘near Maginnis’ ranch, Turtle Cove, John Day river, Upper John Day beds, Oregon,’’ collected by L.S. Davis, 1889. The type is now conserved in the Yale Peabody Museum collection and is numbered YPM-PU 10787.

DISTRIBUTION: Mid- or late Arikareean, John Day Formation, John Day valley, Oregon.

DIAGNOSIS: Wolf-sized species of Temnocyon (basilar skull length,, 26 cm), distinguished from T. altigenis and T. subferox by much larger size, from T. macrogenys by much smaller size, and from the Mammacyon obtusidens – M. ferocior group by retention of the m1 metaconid and possession of a short m2 relative to m1 (ratio E/F,, 1.6 in Mammacyon ;, 1.8 in T. ferox ). T. percussor is distinguished from T. ferox by its taller, broader p3–4 and by its larger more robust m1–2 and M1 (tables 2, 3). T. ferox and T. percussor share a similar m1–2 form but T. percussor represents a larger species. T. fingeruti differs from T. ferox in its more elongate, narrower m1, longer m2, disproportionate size of M1–2 (small M2 relative to M 1 in T. ferox ; large M 2 in T. fingeruti ); dental ratios (table 6); and more inflated frontal region.

REFERRED SPECIMENS: None.

DESCRIPTION: Eyerman described and figured the type specimen of T. ferox (1896: 268–279, pl. 11), reporting that it came from the upper John Day beds, Turtle Cove, Oregon, and so I include here only relevant observations to facilitate comparison with other temnocyonine species of similar size.

The skull and associated mandibles are crushed and fragmented, held together by an extremely hard, indurated gray tuff that preserved the articulated skeleton. Sutures and other fine anatomical details are obscured and distorted. The skull has a basilar length of, 26 cm. The snout is of moderate length: preorbital distance,, 10 cm; postorbital, 16 cm. Relative to Canis lupus the preorbital distance is proportionately shorter and the postorbital longer. The frontals are little inflated, much less so than in T. fingeruti , a carnivore of about the same size. The basicranium unfortunately is so damaged that no details can be identified.

The dentition reflects the plesiomorphic pattern seen in T. altigenis and T. subferox , is simply scaled to larger size, differing most notably in the form of M1–2. The p1 is represented by a single alveolus; p2 and p3 are not robust as in Mammacyon and Delotrochanter but rather low as seen in T. altigenis from Logan Butte—they carry no posterior accessory cusps and have thin enamel ridges traversing their anterior and posterior faces; p4 is distinctly larger than p3 and has a labially placed posterior accessory cusp—p4 has a squared heel with a centrally placed cingulum cusp and is elongate relative to m1 length. The m1 is a short, rather broad carnassial retaining a slightly reduced metaconid; the m1 talonid is nearly entirely occupied by the massive hypoconid (there is no entoconid); the hypoconid is much lower in height than the m1 paraconid. The m2 is short, a striking feature of the species; m1/m2 length ratio is,1.8. The m2 trigonid is dominated by a large protoconid and the talonid by a hypoconid, both labially placed—there is no metaconid and only an extremely reduced paraconid; the trigonid width is 8 mm, and the talonid narrows to a width of 6.6 mm. The m1 hypoconid and m2 protoconid-hypoconid form a linear series of three blunt, crushing cusps.

The upper premolars are also lowcrowned, gradually increasing in height from P1–3. Only P3 has a posterior accessory cusp, very small, somewhat labial in position above a slightly expanded heel with a squared posterior border. Although the upper carnassials are damaged, the metastylar blade was apparently short and the protocone modestly enlarged. M1 still retained a parastyle, and a prominent cingulum surrounded the tooth; the lingual cingulum was thickened, enlarging the protocone region, more so than in T. subferox . M1 retains both preand postprotocristae and the protocone is situated almost exactly in the center of the expanded lingual half of the tooth. M2 is much smaller than M1 and has markedly reduced the metacone; M3 is absent.

Relative to the wolf the upper and lower canines are larger whereas the incisors are the same size. Each lower incisor shows a single accessory cusp (Nebenzacke) on its labial margin.

A partially articulated postcranial skeleton, including the limbs, fore- and hind feet, was found in association with the skull and mandibles and was described by Eyerman (1896). Although difficult to free from the indurated matrix, the skeleton was prepared to demonstrate its limb proportions and digitigrade paraxonic fore- and hind feet. The limbs are discussed in the section on Postcranial Osteology.

DISCUSSION: Temnocyon ferox is distinguished from T. altigenis and T. subferox by larger size, similar to a living wolf, but shares with those species a plesiomorphic temnocyonine dentition. These three species probably form a morphocline in which body size increases through time. T. ferox , however, is the first species in this lineage to show specialization of its carnassials and molars, while still retaining simple low premolars that distinguish this species from T. percussor , T. macrogenys , and the species of Mammacyon and Delotrochanter that have larger more developed premolars. The presence of the m1 metaconid and short m2 are diagnostic features of the molars distinguishing T. ferox from temnocyonines of similar size such as Mammacyon obtusidens (which has no m1 metaconid and a larger, elongate m2) and Temnocyon fingeruti . T. ferox can be distinguished from T. fingeruti using M1–2: the T. ferox M1 shows a more developed lingual cingulum and M2 is much reduced whereas in T. fingeruti the M1 shows only modest expansion of the lingual cingulum and M2 is large. However, the M1 lingual cingula of both T. ferox and T. fingeruti are much less developed relative to the hypertrophied lingual cingula of Mammacyon and Delotrochanter .

Upper carnassials of T. ferox are damaged but appear to be sectorial teeth like those of T. fingeruti ; however, P4 has a prominent protocone more lingually situated than in T. subferox .

The teeth of Temnocyon ferox are similar to the available teeth of T. percussor (p3–m2, M1). The size increase from T. ferox to T. percussor is characterized by development of a taller p3–4 and more robust m 1–2 in T. percussor .

Temnocyon ferox is one of the few temnocyonines for which there is a confirmed association of the cranium and an articulated postcranial skeleton. Eyerman (1896) was aware of the evident disproportion between skull and limbs: the skull was larger than that of the average wolf yet the limbs were noticeably shorter. Limb elongation is nonetheless present, although not to the degree seen in the wolf. When compared with the limb and foot skeleton of the cursorial wolf, T. ferox shows a number of parallel adaptations (see Postcranial Osteology).

Forelimb elongation in Temnocyon ferox is evident relative to the plesiomorphic forelimb of T. altigenis and Daphoenus . As in the wolf, the forelimb of T. ferox exhibits a narrow distal humerus with reduced medial epicondyle, a closely apposed distal ulna and radius (i.e., articular process of the ulna reduced to a smooth planar facet pressed against the distal radius), and a digitigrade paraxonic forefoot with narrow carpus (metacarpals 2 and 5 short; metacarpal 1 reduced). In the hind foot there is a narrow elongated tarsus; long paraxonic metatarsals 3–4; shorter metatarsals 2 and 5; and metatarsal 1 a thin rodlike bone 45 mm in length (not as reduced as the minute triangular nubbin, 1 cm in length, that is the vestige of the first metatarsal of the wolf). Paraxonic metapodials of the fore- and hind foot of the wolf are, 2 to 2.5 cm longer than those of T. ferox . The lengthened radius and ulna and the long paraxonic metacarpals are responsible for the more elongate forelimb of the wolf.

Figures

Fig. 12. Holotype of Temnocyon ferox Eyerman (YPM-PU 10787), from ‘‘near Maginnis’ ranch, Turtle Cove, John Day river, Upper John Day beds, Oregon.’’ A, Cranium in lateral view; B, maxilla with P3–M2 (white plaster fills voids in teeth); C, Eyerman’s (1896) restoration of the holotype cranium and mandible. Note crushing and fragmentation of the cranium in (A).

Fig. 13. Holotype mandibles of Temnocyon ferox Eyerman (YPM-PU 10787), with both canines and left and right p2–m2. Mandibular bone is heavily fractured. Associated forelimb, figure 53.

Fig. 14. Occlusal view of the holotype mandibles of Temnocyon ferox Eyerman (YPM-PU 10787), with left p2–4, m1–2, right p3–4, m1–2. An m1 metaconid is evident on both carnassials (stereopair).

Fig. 53. Articulated right forelimb of the holotype of Temnocyon ferox (YPM-PU 10787), John Day Formation, Oregon. The forefoot shows elongation of the paraxonic metacarpals 3, 4, and their digits, with reduction of metacarpals 1, 2, and 5 (metacarpal 5 is hidden from view). A partial femur (fe) and tibia (ti) of an oreodont were entombed with the beardog. Abbreviations: sc, scapula; hu, humerus, ul, ulna; ra, radius; cp, carpus; nos. 1–4, metacarpals; pr, proximal phalanx; ip, intermediate phalanx.