Microleter mckinzieorum gen. et sp. nov. from the Lower Permian of Oklahoma: the basalmost parareptile from Laurasia

摘要

The Lower Permian fissure fill deposits near Richards Spur (a.k.a. the Fort Sill locality), Oklahoma, have produced a remarkably rich, diverse, and well-preserved assemblage of fully terrestrial tetrapods, including the parareptiles Bolosaurus grandis, Colobomycter pholeter and Delorhynchus priscus. This study describes a superbly preserved new parareptile, Microleter mckinzieorum gen. et sp. nov., recently recovered from the site. The fossil consists of a small, gracile, mostly articulated skull with an attached lower jaw. Distinct sculpturing is present consisting of small pinprick-size pits interspersed among larger round pits, with shallow grooves radiating to the edges of some of the bones, a pattern somewhat similar to both the Oklahoman parareptile Acleistorhinus and the millerettids from South Africa. Microleter also possesses a temporal fenestra, bounded by the jugal, quadratojugal, postorbital and squamosal but open ventrally. In addition to possessing a very broad palatine, there is an indication that the lacrimal reached the naris, a feature shared with more basal parareptiles. A phylogenetic analysis, using both parsimony and Bayesian algorithms, of Palaeozoic parareptiles indicates that Microleter falls fairly basally, between the millerettids and the group including Acleistorhinus and lanthanosuchids. As such this taxon fills a significant gap in our knowledge of Early Permian and basal parareptiles, with interesting implications for biogeography. Whereas previous evidence argued for an initial Gondwanan diversification of parareptiles, the early age and basal phylogenetic position of this taxon and other parareptiles from Laurasia make this hypothesis problematic.