A new drepanosauromorph (Diapsida) from East–Central New Mexico and diversity of drepanosaur morphology and ecology at the Upper Triassic Homestead Site at Garita Creek (Triassic: mid-Norian)

Abstract

ABSTRACT The Late Triassic was home to great tetrapod diversity, with a mixture of endemic Triassic groups and others with extant descendants. These two groups are represented in microvertebrate accumulations, but their fossils are mixed and fragmentary, leading to challenges in confidently identifying them. Among the Triassic endemic groups, drepanosauromorphs are among the most unusual and easily recognized, but many details of their anatomy are obscured by the lack of three-dimensional and matrix-free specimens. Here we describe new material, including a new species, using isolated but three-dimensional drepanosauromorph elements from the Homestead Site at Garita Creek, an Upper Triassic microvertebrate locality near Garita Creek, New Mexico. This site has thus far yielded dozens of isolated drepanosauromorph specimens, including manual/pedal unguals of at least three morphotypes, vertebrae, and caudal unguals (= tail claws). At least two drepanosauromorph species are present based on distinct enlarged ungual morphotypes, with one representing a new Skybalonyx-like species, Unguinychus onyx gen. et sp. nov., and a second form similar to Drepanosaurus. Unguinychus onyx may have been fossorial whereas the second morphotype likely represents an arboreal species, possibly indicating that contemporary drepanosauromorphs had different ecologies. For the first time, we report a potential “small” ungual morphotype, and we present a partial caudal ungual exhibiting features distinct from manual and pedal unguals. The identification of isolated and three-dimensional drepanosauromorph fossils expands the diversity of the clade and demonstrates the usefulness of incorporating microvertebrate data into assemblage studies.