A small derived titanosaurian dinosaur from the Late Cretaceous of Brazil

RIFF, DOUGLAS; GONZALEZ RIGA, BERNARDO; MATEUS, OCTAVIO; MACHADO, ELAINE

Congreso; XXVII Congresso Brasileiro de Paleontologia; 2021

A new titanosaur taxon was found in the Late Cretaceous strata of the Maastrichtian Echaporã Member of the Marilia Formation outcropping in Campina Verde, Minas Gerais state. The fossils were discovered by the first author in 2012 and subsequently collected by his institutional team with the collaboration of the co-authors, together with remains of a second new titanosaur taxon under study. The specimen is housed at Zoological Collection of the Universidade Federal de Uberlândia (INBIO/UFU) under number MBC-033-PV and represented the first finding from the Echaporã Member in Minas Gerais State in almost a century, since the first titanosaurs of the Triangulo Mineiro region were found in this same unit in the municipality of Monte Alegre de Minas by Guilherme Bastos Milward on September 8, 1922. MBC-033-PV includes dorsal vertebrae, dorsal ribs, and caudal vertebrae. The dorsal centra are opisthocoelous like in most macronarians. In the anterior dorsals, the centra are dorsoventrally depressed, particularly in the anterior cotyles which have a mediolateral width to dorsoventral heigh ratio of 1.45-1.5. The neural arch is low and the pre- and postzygapophyseal facets are extraordinarily large. The neural spines are dorsoventrally reduced and the spinoprezygapophyseal laminae do not link dorsally toward the neural spine. In the posterior dorsals, the centra are also dorsoventrally depressed but the neural arch is high. Transverse processes are dorsolaterally directed, over the level of the postzygapophyseal facets. The intrapostzygapophyseal lamina is absent. The neural spine is inclined posteriorly around 40º like Chilean Arackar and most derived titanosaurs. It is thicker dorsally and laterally expanded; moreover, it is laterally supported by the spinodiapophyseal and a double spinopostzygapophyseal laminae. The caudal vertebrae have strongly procoelous and dorsoventrally depressed centra (mediolateral width to dorsoventral heigh ratio of 1.41). Neural spines and postzygapophyseal facets are strongly directed posteriorly, unlike the Brazilian titanosaurs Baurutitan, Trigonosaurus and Uberabatitan. In contrast, this morphology is close to those of Argentinean Saltasaurus and Neuquensaurus. The discovery of this taxon, relatively small (total length estimated 12-13 m) expands the knowledge of the titanosaurian faunas of central South America. The phylogenetic position of this taxon, probably close to Saltasaurinae taxa (up to now only recorded In Argentina and Ecuador) must be tested by a detailed cladistic analysis.