New Mexico Geological Society Annual Spring Meeting — Abstracts

Fossil vertebrates are present at nine localities in the Red Tanks Formation of the Madera Group in the Carrizo Arroyo-Major Ranch area of the Lucero uplift in central New Mexico. All fossil vertebrate localities are in the upper half of the formation; most are in the upper 10m of the Red Tanks section, above the distinctive, locally traceable brackish water limestone bed full of Permophorus and myalinid bivalves. The vertebrate fossils occur mostly as isolated bones and teeth in channel-lag conglomerates or in pedogenic calcrete nodules. They encompass a wide size range from microvertebrate to large pelycosaur. The Red Tanks vertebrate assemblage from these localities includes chondrichthyans, palaeoniscoids, dipnoans (Gnathoriza and Sagenodus?), nectrideans, microsaurs, eryopids (Eryops), diadectomorphs, captorhinomorphs and ophiacodontid, edaphosaurid and sphenacodontid pelycosaurs. The pelycosaurs numerically dominate the assemblage, which contains no obvious pre-Wolfcampian age indicators. Indeed, we assign dermal bone fragments with symmetrical ridge-and-pit ornamentation to the Wolfcampian index Eryops. These are 6-mm-thick, flat bone fragments that display a uniform distribution of x-shaped ridges that separate circular to suboval pits on the external surface. We, therefore, assign the Red Tanks vertebrate assemblage a Wolfcampian (Early Permian) age.