New materials from the Barro Alto site (Rio do Rasto Formation, Guadalupian) and preliminary isotopic (δ18O) data.

FRANCISCHINI, HEITOR; LEA, LEUZINGER; AGUSTIN MARTINELLI; MARINA BENTO SOARES; CESAR SCHULTZ; VENNEMANN, T.

Jornada; Paleo RS - 2017; 2017

The Barro Alto outcrop (Rio do Rasto Formation; São Gabriel, RS) has produced a diverse vertebrate fauna typical of the mid Permian, with the anomodont Tiarajudens eccentricus being one of the most significant taxa. Apart from this species, other materials were collected at the site, such as teeth of Xenacanthiformes (Triodus richterae, materials with affinity to Wurdigneria and other indeterminate genera) and Hybodontiformes (undetermined material), bone fragments and at least seven morphotype of conical teeth and two of ganoid scales attributed to actinopterygians (mainly Paleonisciformes), conical and striated teeth referred to temnospondyls, a large-sized vertebral centrum of uncertain affinity (temnospondyl, lepospondyl or anthracosaur), and a fragment of the distal portion of an Archosauromorpha humerus. New discoveries in the disaggregated sediment collected between 2014?2015 include: a cephalic plate of Hybodontiformes, meso-distally long, short-crowned teeth of euselachians similar to Polyacrodontidae, palatine dental plates of actinopterygians, similar to the present in Phylodontidae; flat and cylindrical teeth referred to Palaeonisciformes Platysomidae; and rhomboidal, little ornamented scales of Actinistia (Coelacanthiformes). These materials come from four distinct levels and account for the high diversity of the Barro Alto paleoichthyofauna. Additionally, we are performing oxygen isotopic analysis (δ18O) at the University of Lausanne (Switzerland) on the fossil material (phosphate from teeth, scales and/or fragments of sharks and bony fish), as well as on the associated carbonatic sediment of the four fossiliferous levels. Since the isotopic composition of fish bio-apatite is derived from the ingested water and is dependent of the temperature, this parameter can be used as a paleoenvironmental proxy. The preliminary results point to similar δ18Op compositions (ranging from 10.9 to 12.2?VSMOW) among different taxa and the distinct levels. These data agree with the freshwater paleoenvironment indicated by the presence of terrestrial tetrapod bones and the abundance of xenacanthiform shark remains in the studied strata. However, they might also indicate a resetting of the isotopic signal caused by diagenesis.