An aberrant stem tetrapod from the early Permian of Brazil

Abstract

Early evolutionary history of tetrapods is typically divided into two major phases: an initial diversification of archaic stem tetrapod groups, and a sudden replacement by temnospondyl amphibians and amniotes following a late Carboniferous dry interval termed the Carboniferous Rainforest Collapse (CRC). However, the degree to which this scenario applies to the early tetrapods of Gondwana is uncertain. Here, we report Tanyka amnicola, gen. et sp. nov., an archaic stem tetrapod from the early Permian of Brazil characterized by strong torsion of the mandibular ramus and a remarkable battery of enlarged denticles on a strongly arched coronoid. The new taxon is assigned to the tetrapod stem based on the presence of a denticulate adsymphyseal and elevated hook-like glenoid surface without a postglenoid area. Phylogenetic analysis shows affinities between this species and stem tetrapods more proximal to the tetrapod crown group, particularly Eucritta and the Laurussian baphetids. This is the second stem tetrapod group known to have survived until the end of the early Permian in Gondwana despite local extirpation in Laurussia, implying that current hypotheses of Carboniferous tetrapod turnover are oversimplified. The unique jaw morphology suggests adaptations to either specialized processing of small invertebrates or consumption of some plant material, demonstrating that stem tetrapods continued to explore new niche space into the Permian of Gondwana.