New data on Guaibasaurus candelariensis, a saurischian dinosaur from the Norian of Brazil

MAX LANGER; AGUSTIN MARTINELLI; A. D. MARSH

Buenos Aires

Jornada; XXX Jornadas Argentinas de Paleontología de Vertebrados; 2016

The holotype specimen of Guaibasaurus candelariensis was collected during 1998 in southern Brazil by a team lead by Jorge Ferigolo and José Bonaparte. Following the discovery of a new specimen in 2002, parts of the holotype were taken to Argentina for further preparation. Among these, the best preserved trunk vertebra was recently found by Stella Alvarez in the Museo Argentino de Ciencias Naturales, identified by Martín Ezcurra, and brought to Brazil by the second author. The vertebra is characterized by an elongated and laterally compressed centrum and a nearly complete neural arch preserved separately, indicating that they were not co-ossified. The parapophysis is close to the diapophysis, suggesting that the vertebra belongs to the caudal half of the trunk. A well-preserved hyposphene is seen as a ventral, vertical extension of the postzygapophyseal surfaces. The vertebral laminae are not well developed, but ridges linking the diapophysis with the zygapophyses and the upper corners of the centrum are clearly observable. These laminae delimit cranial, ventral, and caudal chonoses, the latter of which are delimited caudally by a sub-vertical secondary ridge. Furthermore, this vertebra bears a ridge extending cranioventrally from the parapophysis to the craniodorsal corner of the centrum, feature never before documented.in G. candelariensis. The tibia of G. candelariensis has a lateroventrally tapering outer malleolus and the astragalus bears a reduced fibular facet and a continuous excavation along the cranial and distal surfaces. These features resemble the typical condition found in the newly proposed Tawa + Chindesaurus clade, suggesting that G. candelariensis is not much departed from those taxa in the dinosaur evolutionary tree.