Teyujagua

Teyujagua is known only from a well preserved skull with four associated cervical vertebrae, the only known postcranial material, Skull The skull of Teyujagua is exceptionally well preserved and almost complete, possessing several key features of the archosauriform skull. In total it measures approximately , with a long, broad and flattened snout. Teyujagua possesses a mosaic of characteristics intermediate between basal archosauromorphs and Archosauriformes. Primitive features include the absence of an antorbital fenestra and an open lower temporal bar, however like Archosauriformes it has serrated teeth and an exposed mandibular fenestra on the lower jaw, features previously only found in Archosauriformes. The external nares are dorsally positioned and fused into a single large opening (confluent), a feature found in several aquatic and semi-aquatic Archosauriformes, although the orbits are positioned laterally and slightly forwards, providing limited binocular vision. The nasals are long and occupy much of the skull length, followed by short, broad frontals that are almost excluded from the margin of the orbit by the pre- and postfrontals. The postfrontal bones are sculpted, and the jugals are similarly adorned with longitudinal ridges. The parietal bones surround a small pineal foramen ("third eye"), a feature absent in most archosauriforms but sometimes found in the proterosuchid archosauriform Proterosuchus. The lower temporal fenestra is trapezoidal in shape, another characteristic previously on found in archosauriforms, while the upper temporal fenestrae are slender. A unique feature (autapomorphy) of Teyujagua is that the external mandibular fenestra is positioned unusually far forward on the lower jaw, directly beneath the eyes when the jaw is closed. The dentition is heterodont, bearing four small premaxillary teeth and a maximum of 15 larger maxillary teeth. The dentary tooth row is slightly shorter than the tooth row of the maxilla. The teeth are all laterally compressed and serrated, however unlike later Archosauriformes they are only serrated on their distal (rear) margins. The teeth are also unlike early archosauriform teeth in that they are loosely implanted in deep sockets (thecodont), whereas the earliest archosauriforms had teeth fused to their bony sockets (ankylothecodont). ==Discovery and Naming==

The holotype material, UNIPAMPA 653, was collected from an exposure in the Sanga do Cabral Formation in Southern Brazil, informally known as Bica São Tomé, located in the Paraná Basin. The locality is composed of five outcrops, with UNIPAMPA 653 being found roughly above the base of outcrop 5, in a layer rich in calcareous concretions. The specimen was collected by a team from the Paleobiology Laboratory of the Universidade Federal do Pampa (Unipampa) at the beginning of 2015, The specific name is derived from Greek paradoxa ("paradoxical", "unexpected"), referring to its unusual combination of ancestral and derived archosauriform characteristics. ==Classification==

In a phylogenetic analysis, Teyujagua was recovered as the sister taxon to Archosauriformes, in a more derived position than the Triassic Prolacerta. Pinheiro et al. performed the analysis using a novel data matrix assembled from two previous studies by Martin D. Ezcurra. Their analysis recovered two most parsimonious trees, both recovering a clade made up of Teyujagua and Archosauriformes. This clade is supported by five synapomorphies. The results of their analysis are reproduced and simplified below. }} They also performed another analysis that included the enigmatic and poorly known Permian Eorasaurus, thought to be the oldest known archosauriform. The inclusion of Eorasaurus produced a broadly similar topology to the first analysis, with Teyujagua still occupying a sister position with Archosauriformes. However, it recovered Eorasaurus in an unresolved polytomy with Koilamasuchus, Fugusuchus, erythrosuchids and a clade composed of Euparkeriidae, Proterochampsia and Archosauria. This provides further support of archosauriform affinities for Eorasaurus, and so also supports the presence of archosauriform and archosauromorph ghost lineages extending back into the Permian period, at least into the middle Wuchiapingian of the late Permian. and Teyujagua provides unique insight to the initial acquisition of traits in their early evolution in the Permian, as the skeletal records for Permian archosauriforms are rare and fragmentary. ==Palaeoecology==

The Sanga do Cabral Formation is interpreted as representing a broad, semiarid plain with localised shallow braided stream channels. The most common vertebrate fauna are the procolophonoid parareptiles, particularly the genus Procolophon, as well as the fragmentary remains of temnospondyl amphibians, including the rhytidosteid Sangaia and the capitosauroid Tomeia. Less common are the postcranial remains of other archosauromorphs, and possibly synapsids. The formation is roughly coeval with the Lystrosaurus Assemblage Zone in Karoo, South Africa, and shares a similar composition of Early Triassic fauna. Teyujagua may have been a semi-aquatic ambush predator along the margins of lakes and streams, as suggested by the dorsally positioned nares, similar to some later Crocodyliformes. ==References==