Abstract
After the Permo-Triassic mass extinction, the archosauromorph fossil record is comparatively abundant and ecologically diverse. Among early archosauromorphs, tanystropheids gained considerable attention due to the presence of extreme skeletal adaptations in response to sometimes overspecialized lifestyles. The origin and early radiation of Tanystropheidae, however, remains elusive. Here, a new Early Triassic archosauromorph is described and phylogenetically recovered as the sister-taxon of Tanystropheidae. The new specimen, considered a new genus and species, comprises a complete posterior limb articulated with pelvic elements. It was recovered from the Sanga do Cabral Formation (Sanga do Cabral Supersequence, Lower Triassic of the Paraná Basin, Southern Brazil), which has already yielded a typical Early Triassic vertebrate assemblage of temnospondyls, procolophonoids, and scarce archosauromorph remains. This new taxon provides insights on the early diversification of tanystropheids and represents further evidence for a premature wide geographical distribution of this clade. The morphology of the new specimen is consistent with a terrestrial lifestyle, suggesting that this condition was plesiomorphic for Tanystropheidae.
Highlights
Archosauromorpha comprises an exceptionally diverse clade of diapsids, which originated during the Permian and progressively increased its diversity throughout the Mesozoic and Cenozoic eras
Albeit the matrix of Pritchard et al [6], used in this work, does not include Jesairosaurus lehmani, Elessaurus gondwanoccidens differs from J. lehmani in several characters
Based on the presence of a calcaneal tuber, the hooked fifth metatarsal and the distally bifurcating pleurapophyses on the second sacral vertebra, we propose a terrestrial habit for Elessaurus gondwanoccidens (Fig 6), similar to what is argued for Macrocnemus and Tanytrachelos, and distinct from what is usually proposed for Tanystropheus
Summary
Archosauromorpha comprises an exceptionally diverse clade of diapsids, which originated during the Permian and progressively increased its diversity throughout the Mesozoic and Cenozoic eras. The most critical adaptive radiation of this clade took place following the aftermath of the Permian-Triassic mass extinction, resulting in a wide spectrum of occupation regarding both habitat and ecological niches [1,2]. After the Permian-Triassic crisis, the archosauromorph fossil record is considerably abundant and morphologically diverse, including.
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