Titanosauria: A Critical Reappraisal of Its Systematics and the Relevance of the South American Record

Abstract

Our understanding of sauropodomorph evolution is continually improved with the recognition of newspecies and their inclusion in phylogenetic data sets, along with the incorporation of novel characters. Whereas some subclades remain stable in terms of their original taxonomic content, the definitions of others have proven to be less easily applicable as increased taxon and character sampling has changed sauropodomorph interrelationships. Relatively minor differences in the position of clade specifiers between alternative phylogenies result in substantial differences inclade composition in several instances.Titanosauria is themost successful and diverse clade of sauropodomorph dinosaurs, but its interrelationships are poorly understood. With an ever-growing number of recognized species and increased taxon sampling in phylogenies, resulting in the recovery of newly identified, diverse subclades, the need to re-evaluate titanosaurian supra-specific taxonomy becomes increasingly important. Using fifteen phylogenetic data sets, we conducted a series of analyses to detect the most stable clades and taxa amongst Titanosauria. Based on this, we propose several changes to titanosaur systematics, including a newly defined nodestemtriplet composed of Eutitanosauria and its constituent lineages, Colossosauria and Saltasauroidea, developing a new framework to improve stability and facilitate communication of phylogenetic results.