New Mexico Geological Society Annual Spring Meeting — Abstracts

The sail-backed basal (“pelycosaurian”-grade) synapsid Dimetrodon is one of the most distinctive basal amniotes of the Permian Period. Outside of Texas, the genus has sparse records in New Mexico, Utah, Arizona and Germany. We add to the sparse record of Dimetrodon from New Mexico a recently discovered specimen from the Abo Pass area, Torrance County, consisting of a distinctive elongate neural spine cataloged as NMMNH P-58748. From the lower part of the Cañon de Espinoso Member of the Abo Formation near the Abo mine (NMMNH locality 7765), the incomplete spine has a figure-eight (or dumbbell-shaped) cross-sectional outline, a minimum dorsoventral height of 125 mm and a maximum transverse width of 12 mm. Slender, elongate neural spines with anterior and posterior grooves (forming a figure-eight crosssection) are particularly characteristic of the genus. However, NMMNH P-58748 is too incomplete to assign to a species of Dimetrodon, though it clearly pertains to a small specimen of the genus.

This fossil of Dimetrodon is the fourth record of the genus from New Mexico. Two are from Abo Formation red beds in the Jemez Mountains area of northern New Mexico and a third is from the Loma de las Cañas area, Socorro County. During the time of Abo deposition (middle Wolfcampian-early Leondardian), the Dimetrodon locality reported here was ~ 170 km from the seashore and near the flanks of the Pedernal uplift of the ancestral Rocky Mountain orogeny. This Dimetrodon thus lived in an inland habitat, and this fits the distribution of Dimetrodon fossils in the Abo Formation in New Mexico, which is consistent with it having been a fully terrestrial inland and upland predator. Additional discoveries of Dimetrodon, like that reported here, are needed to fully establish its paleogeographic and paleoenvironmental range, though we expect that full explanation of its varied abundance will remain elusive for some time to come.