TITANOSAURIA: A CRITICAL REAPPRAISAL OF ITS SYSTEMATICS AND THE RELEVANCE OF THE SOUTH AMERICAN RECORD

JOSE CARBALLIDO; ALEJANDRO OTERO; LEONARDO SALGADO; PHILLIP MANNION; AGUSTÍN PÉREZ MORENO

Jornada; 34 Jornadas Argentinas de Peleontología de Vertebrados; 2021

Titanosauria is one of the most successful clades of Sauropoda, not only in terms of species count, but also in their extreme body size disparity (with animals that largely exceeded 50 tons and others that did not reach 5 tons), being the only sauropod group that reached the K-Pg boundary. Despite their importance within Sauropoda, the phylogenetic relationships of titanosaurs become better known only in the last years, after taxon and character sampling of the data sets used in phylogenetic analyses were notably increased. In the light of these, several congruences and discrepancies started to arise amongst different analyses. The presence of clades with completely different taxonomic content (due to different position of their specifier species), as well as the absence of names for referring diverse clades, resulted in a serious problem when attempting to communicate the results. Considering that clade definitions should be ideally done using stable specifier species, we present a new approach to better understand the deep relationships of the clades within Titanosauria. To do this, we studied 15 datasets under PCR-Bremer and PCR-Jackknife scripts in order to identify the clades with high support, obtained after pruning unstable taxa from the reduced consensus used to summarize the results. Based on this approach, we critically re-evaluate the already defined clade names of Titanosauria, proposing a new clade and modifications in the phylogenetic definitions of several important clades, whereas we alert about putative problems with definitions and taxon content for others, as their specifiers are unstable in support analyses.