Untangling the tree or unravelling the consensus? Recent developments in the quest to resolve the broad-scale relationships within Dinosauria

Abstract

The phylogenetic relationships of the major lineages within Dinosauria have come under intense scrutiny in recent years. In 2017, a radical new hypothesis of early dinosaur evolution, the ‘Ornithoscelida hypothesis’, was proposed, prompting a flurry of work in this area. However, instead of untangling the phylogenetic tree of dinosaurs as hoped, this further research unravelled the scientific consensus on dinosaur origins and their early relationships. Multiple hypotheses have now been proposed, including several that position the ‘traditionally’ non-dinosaurian silesaurids within Dinosauria. There is no sign of an emerging consensus, with all possible combinations of the three major dinosaur clades (Ornithischia, Theropoda and Sauropodomorpha) having been recovered by recent phylogenetic analyses. The existence of several ‘wildcard taxa’ and clades with uncertain affinities around the base of Dinosauria complicates efforts to differentiate these hypotheses. Recent studies have suggested that the data sets used to investigate the phylogenetic relationships of Dinosauria might be fatally flawed. The construction of new data sets with a stronger focus on the logical underpinning of characters, in addition to the inclusion of newly described or redescribed taxa, will likely hold the key to resolving this debate.