Historically, dinosaurs were classified into two major groups (Ornithischia and Saurischia) which were thought to have separate origins. More recently, it was realised that these groups shared common ancestry, but the majority of analyses still recovered a clear ornithischian/saurischian dichotomy. Recently, this status quo was challenged by a study (Baron et al. 2017, Nature) that split Saurischia into two clades: theropods + ornithischians (the Ornithoscelida hypothesis) and herrerasaurids +sauropodomorphs. Although controversial, this showed that the ‘traditional view’ was much more weakly supported than previously realised. This work initiated several other studies that found a series of surprising results, such as the inclusion of Silesauridae in Ornithischia. Controversy surrounds all of these relationships and a new synthesis is required to reach consensus on the shape of the early dinosaur evolutionary tree. Moreover, the current uncertainty in these fundamental relationships undermines attempts to understand the tempo and mode of dinosaur macroevolution and its relationship to potential internal and external drivers. This project will assess the many competing hypotheses for early dinosaur relationships using the large amount of new data now available and cutting-edge phylogenetic comparative methods. The resulting evolutionary tree will be used in turn to examine rates of early dinosaur evolution, biogeographic patterns, and their occupation of morphospace through time, using state-of-the-art analytical methods. This will provide new insights into the factors driving the origin and initial diversification of this important vertebrate clade.