Phenacodus

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 : 37

Phenacodus cf. P. matthewi Simpson, 1935

HOLOTYPE: AMNH 17191 , right dentary with m2–3 from Mason Pocket, Animas Formation , Colorado; see Thewissen (1990) for alternative interpretation of type locality.

REFERRED SPECIMEN: RAM 7210, right dentary fragment with p4 and outline of base of p3 from RAM locality V200001, member 4a (fig. 12A).

DESCRIPTION: RAM 7210 represents a small phenacodontid with a p3 broken off at the gum line and a well-preserved p4. The p3 was approximately 6.37 mm in length and 3.52 mm in width, and the p4 is 7.62 mm in length and 5.30 mm in width. The paraconid of p4 is low and small and is shifted labially to the midline of the tooth (fig. 12A) and the metaconid and protoconid are well developed with the protoconid positioned more anterior than the metaconid. Trigonid enamel is crenulated only on the labial side of p4 and is slight. The talonid basin of p4 is well developed and a large hypoconid and slightly smaller entoconid are present.

DISCUSSION: The paraconid and size of the p3 and p4 of RAM 7210 are significantly smaller than Goler Formation p3s and p4s referred to Phenacodus cf. P. bisonensis ( table 10), indicating that RAM 7210 may represent Phenacodus matthewi , the smallest species of Phenacodus . The holotype of P. matthewi is a dentary with m2–3 (AMNH 17191) which can’t be compared directly with RAM 7210, but two other specimens from the type locality (AMNH 56284, AMNH 17193) each have a heavily worn p4. The p4 of AMNH 56284 is 8.02 mm in length and 5.17 in width, similar in dimensions to RAM 7210, but the paraconid of RAM 7210 is significantly smaller than the p4 paraconid of AMNH 56284, which is equal in size to the metaconid or protoconid. Also, trigonid enamel is distinctly crenulated on the labial side and slightly crenulated on the lingual side of the p 4 in AMNH 56284, while trigonid enamel is crenulated only on the labial side of the p 4 in RAM 7210. AMNH 17193 (right p4, m1, and m3), the holotype of “ Phenacodus gidleyi ” ( Simpson, 1935) now referred to P. matthewi ( Delson, 1971; West, 1976; Thewissen, 1990), has a p4 that is 6.91 mm in length and 4.76 mm in width, smaller than either AMNH 56284 or RAM 7210. The paraconid is well developed in AMNH 17193, indicating a closer affinity to AMNH 56284 than RAM 7210. The only other reported p4 of P. matthewi is CM 34292 from the Fort Union Formation in the Wind River Basin of Wyoming ( Thewissen, 1990). CM 34292 is about the same size as RAM 7210, but has a large paraconid, like AMNH 17193 and AMNH 56284. Thus, RAM 7210 is similar in size to p4s referred to P. matthewi , but its small paraconid makes referral to the species uncertain.