Abstract
A paleontologic survey of the western outcrops of the terrestrial Baca Formation has yielded the first Chadronian fossils from New Mexico. Three sites of Chadronian (latest Eocene–early Oligocene) age have produced the cameloid Eotylopus, the creodont ?Hyaenodon, the entelodont Brachyhyops, the oreodont Protoreodon, and a large-horned titanothere, ?Menodus. These genera also are found in the Chadronian Porvenir local fauna of Trans-Pecos Texas.
Vertebrate finds indicate a greater time span for the formation's isolated outcrops than previous workers had accepted. The formation had been considered Eocene, in part on the strength of a specimen of Protoreodon pumilus, an oreodont from alluvial-fan deposits north of Datil. The Chadronian sites lie in fluvial deposits north of Quemado, approximately 60 km to the west. Most Baca vertebrates have been recovered from channel deposits or from float. No site with a concentration of small fossils suitable for screening has yet been discovered; thus, future goals for Baca Formation paleontological work include location of fossils in the still unfossiliferous outcrop areas and location of screening sites.
