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A paleontologic survey of the western outcrops of the terrestrial Baca Formation has yielded the first Oligocene fossils from New Mexico. Three sites of Chadronian (early Oligocene) age are known, and their fauna included the small oreodont Leptomeryx, the cameloid ?Eotylopus, the carnivore Hyaenodon, the entelodont Brachyhyops, and a large-horned titanothere Menodus. All these genera are also found in the Porvenir local fauna, Chadronian of Trans-Pecos Texas.
Vertebrate finds indicate far less contemporaneity of the formation's isolated outcrops than previous workers had accepted. The formation had been considered Eocene, partly on the strength of the discovery of a specimen of Protoreodon pumilis, a late Eocene-early Oligocene oreodont, in alluvial-fan deposits north of Datil. The Chadronian sites lie in fluvial deposits north of Quemado, approximately 60 km 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. Future goals for Baca Formation paleontologic work include location of fossils in the still unfossiliferous outcrop areas and location of screening sites.
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