Abstract

Bomburia and Ellipsodon are poorly known taxa from the early Paleocene of western North America. New fossil material from New Mexico expands morphological information and allows taxonomic revision of these taxa. Bomburia is a valid genus, whereas Platymastus palantir, previously considered to be a loxolophine arctocyonid, is probably a junior synonym of B. prisca and as such reveals the upper molar morphology of this taxon.

Ellipsodon is highly derived relative to other mioclaenid condylarths. It has a reduced mesial dentition, with the probable loss of the P1/p1. P2–3/p2–3 are reduced and show a simple incisor-like morphology. M1/m1 and especially M2/m2 are simple with highly inflated protocones/ protoconid-metaconids accentuating a mortar-and-pestle-like chewing function. The M3/m3 are more reduced than in any other mioclaenid.

Mioclaenidae is monophyletic and endemic to western North America. There is no support for a close relationship between Mioclaenidae and South American or African ungulates.

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