Stegotretus agyrus, a new genus and species of microsaur (Amphibian) from the Permo-Pennsylvanian of New Mexico

Abstract

A new genus and species of tuditanomorph microsaur, Stegotretus agyrus, is based on a large series of specimens that includes numerous skulls with some associated postcranial skeletons. All the specimens were collected from a Permo-Pennsylvanian horizon of the Cutler Formation near Arroyo del Agua, north-central New Mexoico. S. agyrus is the only unquestionable microsaur to be reported from New Mexico. On the basis of shared-derived characters S. agyrus is considered most closely related to the more specialized Pantyls and is assigned to Pantylidae. The family is redefined on synapomorphies uniting S. agyrus and Pantlylus, and it is recommeneded that the poorly known Trachystegos, the only other genus assigned to the family, be removed as indeterminate and relegated to family incertae sedis. With one exception the S. agyrus specimens were found in association with a surface lag of caliche nodules and calcite-rich siltstone pebbles, suggesting an original association with an overbank facies. The composition and paleogeographic distribution of two discrete lithofacies assemblages in the general collecting area reinforces this interpretation. It is speculated that the S. agyrus specimens may represent an aestivation assemblage. A partial lower jaw from a Lower Permian horizon of the Cutler Formation of the same area, whose only previous description has been a very brief statement of its closeness in form to Pantylus, is described and illustrated. A tentative assignment to Pantylidae is recommended.