REEVALUATION OF POPO AGIE FORMATION (LATE TRIASSIC, WYOMING) METOPOSAURIDS IN THE UNIVERSITY OF MISSOURI COLLECTION

Metoposaurids are a clade of Late Triassic temnospondyl amphibians that are common constituents of freshwater ecosystems across Laurasia and northern parts of Gondwana. Branson and Mehl (1929) named two metoposaurid species from the Popo Agie Formation of Wyoming in the University of Missouri collections, Koskinonodon princeps and Borborophagus wyomingensis. Metoposaurids from Europe, Morocco, India, and the Chinle Fm of North America have been revised over the course of the 21st century, but those of the Popo Agie Fm are among the most poorly known and have been largely overlooked since their description 90 years ago. Borborophagus wyomingensis and K. princeps have been considered junior synonyms of Buettneria perfecta, which itself was re-named as Koskinonodon perfectus, and most recently as Anaschisma browni. Branson and Mehl’s study did not include detailed redescription or figures of these specimens, which has limited the utility of their study and the specimens, which represent the northernmost extent of A. browni. The general understanding of metoposaurid systematics and paleobiology has undergone recent revisions, but redescription of junior synonyms can help clarify the intraspecific variation within recognized taxa. We present detailed redescriptions of these historically important specimens and contextualize their anatomy within the current framework of metoposaurid paleobiology. Several synapomorphies unite the type specimens of B. wyomingensis, K. princeps, and A. browni such as a contribution of the lacrimal to the orbital margin and posteriorly tapering frontals. This helps clarify phylogenetically informative character states missing or obscured in the holotype of A. browni, in particular those involving the anterior and lateral skull margins such as the anterior extent of the jugal. Anaschisma browni is the most geographically dispersed metoposaurid, ranging from Wyoming to Arizona in western North America and possibly as far east as Pennsylvania. A greater appreciation of intraspecific variation over temporal and geographic scales in this well-represented taxon can more broadly inform on interpretations of temnospondyl anatomy and taxonomy.