The braincase of a specimen of Proterochampsa Reig (Archosauriformes: Proterochampsidae) from the Late Triassic of Argentina

The proterochampsids are a Triassic group of superficially crocodile-like forms belonging to the Archosauriformes. In the present contribution, we present new information regarding the braincase of the proterochampsid Proterochampsa Reig 1959, from the Ischigualasto Formation (Carnian) of Argentina, and discuss its phylogenetic considerations. Some unique neurocranial features of Proterochampsa are described, including: the prominence and thickness of the V-shaped ridge that surrounds the basisphenoidal fossa; the medially concave lateral arms of the same ridge; and the semilunar depression on the parabasisphenoid ventrolaterally exposed. Other features are only shared with likely unrelated archosauriforms, including: the great lateral development of the basipterygoid processes and caudal development of its distal end; an eight-shaped metotic foramen; laterally directed basipterygoid processes; and rostral boundary of the basisphenoidal recess V-shaped. Proterochampsa differs in many other aspects from the archosauriform Chanaresuchus, including: a proportionally shorter basioccipital basal tubera; cultriform process ovoid in cross-section; longitudinal sulcus dorsal to the basipterygoid process; deep basisphenoidal recess; and the absence of a prominent intertuberal plate. In many braincase features, Proterochampsa is more similar to archosaurs than to Euparkeria, erythrosuchids and Proterosuchus. They include a reduced semilunar depression. A ventral border of the basioccipital forming a wide convexity and a dorsoventrally thin paroccipital process likely represents a feature shared with Chanaresuchus, but not with Doswellia and other basal archosauriforms.Fil: Trotteyn, Maria Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan; Argentina. Universidad Nacional de San Juan; ArgentinaFil: Haro, Jose Augusto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Juan; Argentina. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones Paleobiológicas; Argentin

The Origin and Early Evolution of Sauria: Reassessing the Permian Saurian Fossil Record and the Timing of the Crocodile-Lizard Divergence

Sauria is the crown-group of Diapsida and is subdivided into Lepidosauromorpha and Archosauromorpha, comprising a high percentage of the diversity of living and fossil tetrapods. The split between lepidosauromorphs and archosauromorphs (the crocodile-lizard, or bird-lizard, divergence) is considered one of the key calibration points for molecular analyses of tetrapod phylogeny. Saurians have a very rich Mesozoic and Cenozoic fossil record, but their late Paleozoic (Permian) record is problematic. Several Permian specimens have been referred to Sauria, but the phylogenetic affinity of some of these records remains questionable. We reexamine and review all of these specimens here, providing new data on early saurian evolution including osteohistology, and present a new morphological phylogenetic dataset. We support previous studies that find that no valid Permian record for Lepidosauromorpha, and we also reject some of the previous referrals of Permian specimens to Archosauromorpha. The most informative Permian archosauromorph is Protorosaurus speneri from the middle Late Permian of Western Europe. A historically problematic specimen from the Late Permian of Tanzania is redescribed and reidentified as a new genus and species of basal archosauromorph: Aenigmastropheus parringtoni. The supposed protorosaur Eorasaurus olsoni from the Late Permian of Russia is recovered among Archosauriformes and may be the oldest known member of the group but the phylogenetic support for this position is low. The assignment of Archosaurus rossicus from the latest Permian of Russia to the archosauromorph clade Proterosuchidae is supported. Our revision suggests a minimum fossil calibration date for the crocodile-lizard split of 254.7 Ma. The occurrences of basal archosauromorphs in the northern (30°N) and southern (55°S) parts of Pangea imply a wider paleobiogeographic distribution for the group during the Late Permian than previously appreciated. Early archosauromorph growth strategies appear to be more diverse than previously suggested based on new data on the osteohistology of Aenigmastropheus