New Mexico Geological Society Annual Spring Meeting — Abstracts

Two localities within the lower Eocene San Jose Formation yield numerous fossils of the early Eocene mammal Meniscotherium chamense. The AMNH 150 locality (NE1/4, SW1/4, SW1/4,sec. 31, T25N, R1W) in the Tapicitos Member produced at least 43 individuals of M. chamense. Fossil bones are complete but disarticulated in patches within a 7-to-13-cm-thick interval of poorly sorted, muddy to fine sandy siltstone with 1-cm-thick vertical burrows and calcium carbonate concretions. The bone bed lies about 7 m below a trough-cross-bedded sandstone. 68 long bone orientations plot as two perpendicular modes in a nearly horizontal plane, and the bone assemblage is depleted of bones of Voorhies Group I, implying slight movement by shallow running water.

UNM locality JIC-E147 (NE1/4, SE1/4, NW1/4, sec 22, T23N, R2W) in the Regina Member yielded at least 46 individuals of M. chamense. The relatively narrow boneproducing interval is about 50 m from a laterally adjacent trough-cross-bedded channel sandstone. The remains of M.
chamense are found as complete and incomplete articulated skeletons and disarticulated complete bones and bone fragments. The main bone-containing interval, filling aI paleo-depression, is about 80 cm thick and is a poorly sorted muddy to fine sandy siltstone almost completely devoid of burrows. Both articulated and disarticulated bone was found as much as 1.2 m above the main bone producing layer suggesting reworking and repeating burials.

The two localities share several associated taxa which include coryphodon sp., Hyracotherium sp., Saniwa ensidens, and Crocodilia. Both represent little transported, catastrophic death assemblages, buried in overbank deposits of proximal floodplain environments.