Thryptacodon sp.

Lofgren, Donald, Mckenna, Malcolm, Honey, James, Nydam, Randall, Wheaton, Christine, Yokote, Bryan, Henn, Lexington, Hanlon, Whitney, Manning, Stephen & Mcgee, Carter, 2014, New records of eutherian mammals from the Goler Formation (Tiffanian, Paleocene) of California and their biostratigraphic and paleobiogeographic implications, American Museum Novitates 2014 (3797), pp. 1-60 : 19

Thryptacodon sp.

REFERRED SPECIMEN: RAM 9041, right m1 from RAM locality V200510, member 4a ( fig. 6A ).

DESCRIPTION: RAM 9041 is missing the metaconid due to breakage, but the protoconid, hypoconid, hypoconulid, and entoconid are all well preserved ( fig. 6A ). A small paraconid is connected to the protoconid by a long and arcuate paracristid. Broadly and deeply basined, the talonid is significantly longer and slightly wider than the trigonid. The hypoconid is large and the entoconid and hypoconulid are much smaller, with the hypoconulid slightly smaller than the entoconid. The hypoconulid is markedly shifted lingually, positioned immediately adjacent to the entoconid, so that the two cusps appear twinned, and a small entoconulid is present. The talonid basin is deepest against the back wall of the trigonid and a talonid notch is not present. A prominent shelflike labial cingulid extends continuously from the anterior face of the trigonid below the paraconid, across the protoconid, to the most labial margin of the hypoconid. On the posterior face of the talonid a shelflike postcingulid descends labially to the posterolabial corner of the hypoconid, where only a short gap separates it from the posterior terminus of the labial cingulid.

DISCUSSION: RAM 9041 is most closely aligned with oxyclaenids and is most similar to Thryptacodon , based upon crown height, and occurrence and relative position of primary and secondary cusps. Based on size, RAM 9041 is much smaller than Thryptacodon antiquus , T. australis , and T. pseudarctos and is most similar to specimens included by Gazin (1956) in T. demari and T. belli , which were synonymized by Van Valen (1978) as T. demari . Similarities of RAM 9041 with T. demari include paraconid lingual and positioned anteriorly, talonid basin much wider than trigonid, distinct entoconulid, talonid notch closed, and hypoconulid lingually displaced and close to the entoconid. Only its smaller size and presence of a strong labial cingulid keep RAM 9041 from being identified as the Bison Basin species, now synonymized with T. orthogonius ( Scott et al., 2002) . RAM 9041 measures 4.95 mm in length, with a trigonid width of 2.64 mm and talonid width of 3.05 mm, compared to the m1 of the holotype of T. “ belli ” (UW 1045), whose length and width are 5.6 mm and 3.8 mm respectively ( Gazin, 1956). Thus, RAM 9041 is assigned to Thryptacodon species indeterminate until more specimens are recovered of this oxyclaenid.

Family ARCTOCYONIDAE Murray, 1866

Figures

FIGURE 6. Dentition of oxyclaenids and arctocyonids. A. Occlusal view of RAM 9041, right m1 of Thryptacodon sp. from RAM locality V200510. B. Occlusal view of RAM 15622, right dentary fragment with talonid of p4, and m1–2 of Mimotricentes tedfordi from RAM locality V201014; C. oblique labial view of RAM 15622. D. Occlusal view of RAM 9670, left dentary fragment of Mimotricentes tedfordi with damaged m1 and base of p4 from RAM locality V200510. E. Occlusal view of RAM 6928, right dentary fragment of Mimotricentes tedfordi with m3 talonid and base of trigonid from RAM locality V200001. F. Occlusal view of RAM 9040, right M1 of Lambertocyon cf. L. gingerichi from RAM locality V200001. G. Occlusal view of RAM 9043, left p3 fragment of Lambertocyon cf. L. gingerichi from RAM locality V200001. H. Occlusal view of RAM 9660, premolar of undetermined arctocyonid from RAM locality V200613.