Bone microstructure analyses in ontogenetic series of Mesosaurus tenuidens from the early Permian of Brazil.

Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well-known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central-west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay.

Replacement tooth in mesosaurs and new data on dental microanatomy and microstructure.

The Permian mesosaurs are well known for being the earliest amniotes to exhibit adaptations for living in a marine environment (Irati-Whitehill Sea). In addition to their set of skeletal features associated with aquatic dwelling life, their dentition includes important characteristics related to feeding in this habitat, which is described in this work, based on the analysis of mesosaur specimens from the Lower Permian Irati Formation of Brazil. Mesosaurs have several slender, conical teeth bordered by enamel apicobasal ridges, a feature predominantly found in aquatic amniotes.

A new Xenacanthiformes shark (Chondrichthyes, Elasmobranchii) from the Late Paleozoic Rio do Rasto Formation (Paraná Basin), Southern Brazil.

The Brazilian records on Xenacanthiformes include teeth and cephalic spines from the Parnaíba, Amazonas and Paraná basins. This work describes a new species of Xenacanthidae, collected in an outcrop of Serrinha Member of Rio do Rasto Formation (Wordian to Wuchiapingian), Paraná Basin, municipality of Jacarezinho, State of Paraná. The teeth of the new species are two or three-cuspidated and the aboral surface show a smooth concavity and one rounded basal tubercle.