Temnocyon cf. T. subferox, 1878

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 : 36-37

Temnocyon cf. T. subferox Figure 11

Temnocyon cf. T. altigenis: Stock, 1933b: 35–37 , pl. 1, fig. 6.

REFERRED SPECIMEN: LACM 470, right mandible with c, single-rooted p1 alveolus, alveoli of p2, damaged p3–m2, including anterior part of ascending ramus, from Kew Quarry, Las Posas Hills, CIT loc. 126, Sespe Formation, Ventura County, California, collected by Thurston, 1930, early Arikareean.

DESCRIPTION: The crushed and fragmented lower jaw was accurately described and figured by Stock (1933b: 35–37). Premolars are closely spaced but not crowded, and p3–4 are tall, more so than in T. altigenis . The m1 is larger than any T. altigenis carnassial (table 2): both trigonid and talonid are broadened relative to T. altigenis . The m1/m2 length ratio is estimated at,1.8, similar to T. ferox , taking into account damage to both molars—there is a relatively short plesiomorphic m2. The preserved lower teeth (p3– m2) are all slightly wider and more robust than these teeth in T. altigenis (table 2). The mandible is only 25 mm in depth below the hypoconid of m1, its width much compressed by crushing.

DISCUSSION: The Kew Quarry mandible from the Sespe Formation displays differences in size and proportion of the posterior premolars and molars that argue against its placement in T. altigenis . The upper teeth of Temnocyon subferox (YPM 10065) satisfactorily occlude with the teeth of the Kew Quarry jaw, and indicate a carnivore of approximately the same size. However, there is no associated mandible with the holotype skull of T. subferox (YPM 10065) nor is there any other mandible of appropriate size from the John Day beds that can be referred to the skull. The dentary itself is not diagnostic but is quite shallow as would be predicted for T. subferox .

An important contrast exists between the Kew Quarry mandible and the holotype mandible of Delotrochanter petersoni n. sp. (CM 1603). CM 1603 belonged to a carnivore only slightly larger than the Kew Quarry animal, yet its p2 is short, with a large posterior and a small anterior root, placed very close together. The Kew Quarry p2 is elongate, and its two roots are of about equal size and spaced well apart. Thus the Kew Quarry carnivore does not approach Delotrochanter in premolar form, since the p2 is a key derived trait of the latter genus, nor does its m1 show the straight (as opposed to sinuous) labial cingulum found in Delotrochanter . The Kew Quarry animal cannot be referred to Mammacyon because it lacks shared derived dental traits of that genus: the notched lingual margin of the m1 talonid and the elongate m2. It is more likely that the Kew Quarry mandible belongs to a carnivoran similar to the John Day Temnocyon subferox that retained the shearing dentition typical of the Temnocyon lineage. Fossil mammals found with LACM 470 in Kew Quarry favor an early Arikareean age for the quarry assemblage (see discussion in Age and Correlation).

Figures

Fig. 11. Temnocyon cf. T. subferox (LACM 470), right mandible with p3–m2, damaged c, p1–2, from Kew Quarry, Sespe Formation, Ventura Co., California. This is the only record of the subfamily in western North America other than fossils from the John Day region.