Morphology, Ontogeny, and Phylogenetic Relationships of the Permo-Carboniferous tetrapod Brachydectes newberryi from the Council Grove Group, Nebraska, USA

Abstract

Lysorophia is a poorly-understood group of fossil tetrapods known from the Late Carboniferous and Early Permian of North America. Some prior workers have noted similarities between lysorophians and modern amphibians, suggesting that lissamphibians may have evolved from lysorophian-like ancestors. I used high resolution x-ray micro-computed tomography (HR-XCT) to study skulls of the lysorophian Brachydectes newberryi from the Early Permian of Kansas and Nebraska, USA. I present a detailed description of the skeletal morphology of these skulls, including fine structure of the braincase. With reference to the skeletal morphology described here, I present a list of new, phylogenetically-informative characters from the braincase and incorporate these into phylogenetic analysis of early tetrapods. Lysorophians are found to be microsaurs, a diverse group of early tetrapods. The data presented here suggest that lysorophians and microsaurs may be early reptiles and thus not relevant to the discussion of lissamphibian origins.