PBDB Taxon

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Merycoides stouti

Mammalia - Merycoidodontidae

Taxonomy

Phenacocoelus stouti was named by Schultz and Falkenbach (1950). Its type specimen is F:AM 44839, a skull (Skull with I1-I2 alv. and I3-M3), and it is a 3D body fossil. Its type locality is Guernsey, which is in a Harrisonian terrestrial horizon in the Marsland Formation of Wyoming.

It was synonymized subjectively with Merycoides longiceps by Lander (1998); it was recombined as Merycoides stouti by Stevens and Stevens (2007), Stevens et al. (2023).

Year	Name and author
1950	Phenacocoelus stouti Schultz and Falkenbach p. 107 figs. 1-3, 11, 13-15
2007	Merycoides stouti Stevens and Stevens p. 163
2023	Merycoides stouti Stevens et al. p. 30 figs. Figure 23D-F; Appendix 1D; Table A6

Reference	Diagnosis
C. B. Schultz and C. H. Falkenbach 1950	SKULL: Largest known form of the genus; frontals rounded laterally; nasal retracted anteriorly to a point above anterior portion ofP1; anterior nasal-maxillacontact inregion above P2;typical round supraorbital foramen present (not an oblong vacuity as in P. typus or elongated slot-like depression as in P. kayi), with prominent groove extending forward and downward on side of face to ap- proximately the anterior border of large lacrimal fossa; zygomatic arch moderately heavy, with gradual rise posteriorly, extending to and above posterior border of post-glenoid process (similar to arch of P. kayi, not U-shaped in outline as in P. typus); malar deeper than in other species of genus; infraorbital foramen above P4 , enlarged; bulla similar to that of P. kayi, with inferior surface more depressed towards basioccipital than in P. typus; postglenoid process robust, wide transversely. MANDIBLE: Largest of genus; similar in shape to that of P. kayi; ramus shallower than examples of P. typus; inferior border with more downward curve below M3 than in other species of genus. DENTITION: Superior and inferior series longer and more robust than in other species of Phenacocoelus; C/ and P1moderately large and heavy; premolars not crowded, tendency to slight diastema between P1 and P2 ; p1 usually set at slight angle to alveolar border; Pr-P3 each set at slight angle to alveolar border; weak posterior intermediate crest developed on P2. LIMBS:Approximately same length as examples of P. kayi; considerably longer than those of P. typus; more robust than in either of these two species.
M. S. Stevens et al. 2023	Largest species of Merycoides (M1-3 length =57-63 mm).

Time interval	Ma	Country or state	Original ID and collection number
Harrisonian	23.1 - 18.5	USA (Wyoming)	Phenacocoelus stouti (type locality: 17788 17793 17824 17833 17835 17839 17849 17854)
Harrisonian	23.1 - 18.5	USA (South Dakota)	Phenacocoelus stouti (17748)
Harrisonian	23.1 - 18.5	USA (Nebraska)	Phenacocoelus stouti (17805)