Comparative cladistics on Basal Sauropodomorpha

Basal Sauropodomorphs have been thoroughly studied in recent years. Several hypotheses on the interrelationships within this group have been proposed, ranging from a complete paraphyly, where the group represents a grade from Basal Saurischia to Sauropoda, to a group on its own. The grade-like hypothesis is the most accepted, however the relationships between the different taxa are not consistent amongst the proposed scenarios. These inconsistencies have been attributed to missing data and unstable (i. e., poorly preserved) taxa, nevertheless, an extensive comparative cladistic analysis has found that these inconsistencies come from the character coding and character selection, plus the strategies on merging data sets. This analysis also produced the largest and most comprehensive matrix after the reassessment and operationalisation of every character applied to this group far. Furthermore, partition analyses performed on this data set have found consistencies in the interrelationships within Basal Sauropodomorpha, and has cast doubt on the validity of several clades and taxa, such as Massospondylidae, Massospondylus, Yunnanosaurus, and Coloradisaurus. The results of these studies also highlight a different scenario on how quadrupedality evolved, independently originating twice within the group, and provide a better framework to understand the palaeo-biogeography and diversification rate of the first herbivore radiation of dinosaurs.