Taxon sample and character coding deeply impact unstable branches in phylogenetic trees of dinosaurs

Abstract

Recently, a new completely unorthodox phylogenetic hypothesis regarding both early dinosaurian taxa and major less inclusive groups has been suggested. Immediately after, several new datasets have been produced, resulting in interesting ways to test affinities of distinct taxa. Accordingly, we here aim to access the affinities of the enigmatic Chilesaurus in the most comprehensive and updated data-set of early dinosaurs and its derived inner branches. As a result, Chilesaurus was recovered as the basalmost member of Ornithischia, as recently suggested. However, the inclusion of this taxon in the up to date data-set also generated deep topologic changes in the topology of the strict consensus tree in comparison to those produced in the former study. The analysis nested ornithischians and theropods in a sister-group relationship, instead the traditional saurischian-ornithischia dichotomy, supporting the existence of the clade Ornithoscelida, which demonstrates how a single operational taxonomic unit can produces deep rearrangements on the branches of the phylogenetic tree of dinosaurs.