Sarkastodon: not a giant oxyaenid

Sarkastodon mongoliensis (Granger 1938; AMNH 26641; preserved skull length 37cm; Eocene, 35mya; Fig. 1) was originally considered close to the creodont marsupial, Oxyaena. Here in the large reptile tree (LRT, 1346 taxa, subset Fig. 2) this bear-like carnivore nests in the Carnivora between the wolverine, Gulo, and the seal (Phoca) clade + the Stylinodon clade.

Distinctly the robust nasal of Sarkastodon hangs over the naris, only two robust procumbent premaxillary teeth are present and the multicusp molars have blunt tips, ideal for bone or shell cracking.

Figure 1. Skull of Sarkastodon mongoliensis (Granger 1938) nests not with the creodont marsupial, Oxyaena, but with the wolverine and short-face bear at the base of the seal + Stylinodon clades.

Figure 1. Skull of Sarkastodon mongoliensis (Granger 1938) nests not with the creodont marsupial, Oxyaena, but with the wolverine and short-face bear at the base of the seal + Stylinodon clades.

Sarkastodon is derived from 
wolverines, basal to seals and walruses (Fig. 2).

Figure 1. Subset of the LRT focusing on Basal Mammalia including Creodonta.

Figure 1. Subset of the LRT focusing on Basal Mammalia including Creodonta.

Note
another similar, but smaller traditional oxyaenid, Patriofelis was added to the LRT, nesting between Gulo and Sarkastodon.

Figure 3. Patriofelis skull in two views.

Figure 3. Patriofelis skull in two views. This wolverine-like taxon nests basal to Sarkastodon.

Note the spreading metacarpals and metatarsals
in this taxon (Fig. 4) heading back to the water.

Figure 4. Patriofelis museum mount. This is the sort of wolverine (genus: Gulo) that evolves into seals and walruses.

Figure 4. Patriofelis museum mount. This is the sort of wolverine (genus: Gulo) that evolves into seals and walruses. Sea lions arise elsewhere.

References
Granger W 1938. A giant oxyaenid from the Upper Eocene of Mongolia. American Museum Novitates 969:1–5.
Leidy J 1873. Contributions to the extinct vertebrate fauna of the Western Territories, Rep. US Geol. Surv. Terr. (Hayden), vol. 1, pt. 1, pp. 7-358 (114-116, 316), pis. 1-37.

wiki/Patriofelis
wiki/Sarkastodon

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