Taxonomic revisions on nimravids and small feliforms (Mammalia, Carnivora) from the Upper Eocene of Mongolia

Abstract

This study reports occurrences of feliform carnivorans from the Upper Eocene Ergilin Dzo Formation and Alag Tsav locality of southeastern Mongolia. Nimravus mongoliensis (Nimravidae) is distinguished from other species in having a deep mandible, a longer p/1–2 and m/2 relative to p/4, and relatively wider P3/. Eofelis sp. (Nimravidae), a genus previously known only from the Oligocene of France is found in the Ergilin Dzo Formation. Alagtsavbaatar indigenus comb. nov. (Alagtsavbaatar gen. nov.; Feliformia) is established for new specimens from the Ergilin Dzo Formation and the previously known Stenoplesictis specimen from the Alag Tsav locality based on its characteristics such as moderately developed buccal cingulid and cingular and accessory cuspids on p/3 − 4, wide m/1 trigonid and double-rooted m/2 with a trenchant talonid. Stenoplesictis simplex from the Ergilin Dzo Formation is revised to Asiavorator gracilis, extending its chronological range back to the Late Eocene. Geographical and chronological distributions and morphological comparisons suggest that the Nimravidae originated by the Middle Eocene in southern East Asia and migrated northward in the Late Eocene, whereas the early small feliforms immigrated to northern East Asia in the Late Eocene and stayed within the middle-to-high-latitude area.