New Mexico Geological Society Annual Spring Meeting — Abstracts

The lower Permian Yeso Group records arid coastal plain, shallow marine, and evaporitic deposition across much of central New Mexico. Generally considered to have few fossils, recent study of Yeso Group strata has discovered a diverse fossil record of marine micro-organisms (mostly algae and foraminiferans), terrestrial plants, and tetrapod footprints. We report here the first discovery of a tetrapod body fossil in the Yeso Group—a partial skeleton of a basal synapsid, varanopidae eupelycosaur. The fossil is the natural casts of bones in two pieces, part and counterpart, that were preserved in a sandstone bed of the lower part of the Arroyo de Alamillo Formation in the southern Manzano Mountains. The fossil-bearing sandstone is fine-grained, quartz rich, and pale reddish brown to grayish red unweathered, weathers to blackish red, and is in part encrusted by white caliche. The casts preserve part of the pelvis(?), 18 caudal vertebral centra, both femora and tibia-fibulae, and most of the pedes, largely in close articulation, of a single individual. The skeleton is of a relatively small (femur length = 62 mm, total length of the preserved cast from the pelvis to tip of the incomplete tail = 325 mm) and gracile eupelycosaur most similar to Varanops. Various early Permian eupelycosaurs are known from the older strata of the Bursum Formation, Abo Formation, and Cutler Group in New Mexico, so this discovery extends the eupelycosaur fossil record into younger, early Permian strata. It also indicates that a substantial terrestrial food chain must have been present on the arid coastal plain during deposition of the Arroyo de Alamillo Formation, as the varanopid is a relatively large, early Permian predator that likely fed on smaller vertebrates and arthropods. Furthermore, this discovery indicates the potential of additional discoveries of tetrapod body fossils in Yeso Group strata.