Miocene giants of Brazil: new material of Mourasuchus and Gryposuchus (Crodocylia) from Price's expedition

Abstract

Relevant fossils are continuously been (re)discovered and studied even around forty years after the completion of the RadamBrasil Project. This project was dedicated mainly to the geographic and geological exploration of several regions of the Brazilian territory, especially the Amazon. It was in force from 1970 to 1985, recovering significative amount of fossils under the auspices of RadamBrasil expeditions, including those collected by emeritus paleontologist L.I. PRICE in the north of Brazil, and then guarded in competent institutions for subsequent studies. A vast quantity of this material can be found in the collection of the Museu de Ciências da Terra (MCTer/SGB), in Rio de Janeiro. After recent and thorough review of these fossils, material still new to science can be, and are, found, among which part of the mandible of the holotype of Mourasuchus amazonensis (MCT.R.526) stands out, as well as mandibular material from a smaller individual (MCT.LE .6923) of the same species, in addition to a symphyseal portion of gavialoid Gryposuchus sp (MCT LE 6249). Initially the specimens had been inadequately stored so curatorial actions were carried out to reverse this situation, including cleaning, stabilizing and consolidating fragmented parts and reconditioning recovered specimens, as well their inventory. Mourasuchus amazonensis was a giant suction/filter-feeding alligatoroid, and new material display elongated and low hemimandibular rami; laminar splenial strongly articulated with the dentary; teeth implanted in isolated and well-spaced sockets in the anterior region of the mandible, bearing gradual reduction in size, progressively closer to each other towards the end of the tooth series, with the most posterior ones implanted in alveolar troughs. The teeth are conidont with smooth carinae and apicobasal grooves on the crowns, especially on the lingual surfaces. The mandible of the giant piscivorous Gryposuchus sp. bears nine alveoli in a long and shallow symphysis region, the tip of first alveoli diverging in a V-shaped, and the anterior portion that comprises the first two alveoli laterally expanded. All material come from the greenish to reddish siltstones of the Solimões Formation (Miocene/Pliocene of Acre Basin), at Alto Rio Juruá locality, Acre State. The deposits of the Solimões Formation, formed in a fluvio-lacustrine are characterized by massive mudstones / siltstones or with horizontal lamination and lenticular layers of fine to coarse sandstones with small to medium cross-bedding. The study of fossil vertebrates from de Solimões Formation will provide new information regarding taxonomy, phylogeny and paleobiology, as well as new biostratigraphic data.