2 SYNOPSIS Crown group Archosauria, which includes birds, dinosaurs, crocodylomorphs, and several extinct Mesozoic groups, is a primary division of the vertebrate tree of life. However, the higher-level phylogenetic relationships within Archosauria are poorly resolved and controversial, despite years of study. The phylogeny of crocodile-line archosaurs (Crurotarsi) is particularly contentious, and has been plagued by problematic taxon and character sampling. Recent discoveries and renewed focus

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... on archosaur anatomy enable the compilation of a new dataset, which assimilates and standardises character data pertinent to higher-level archosaur phylogeny, and is scored across the largest group of taxa yet analysed. This dataset includes 47 new characters (25% of total) and eight taxa that have yet to be included in an analysis, and total taxonomic sampling is more than twice that of any previous study. This analysis produces a well-resolved phylogeny, which recovers mostly traditional relationships within Avemetatarsalia, places Phytosauria as a basal crurotarsan clade, finds a close relationship between Aetosauria and Crocodylomorpha, and recovers a monophyletic Rauisuchia comprised of two major subclades. Support values are low, suggesting rampant homoplasy and missing data within Archosauria, but the phylogeny is highly congruent with stratigraphy. Comparison with alternative analyses identifies numerous scoring differences, but indicates that character sampling is the main source of incongruence. The phylogeny implies major missing lineages in the Early Triassic and may support a Carnian-Norian extinction event. crurotarsan clade is most basal and which taxa are most closely related to crocodylomorphs. Although numerous studies have been published, many are preliminary, limited, or unsatisfactory. Most recovered phylogenies are poorly supported on the whole, with crurotarsan ingroup relationships especially prone to mediocre support values (Gower & Wilkinson 1996). More fundamentally, many analyses are characterised by limited or problematic taxon and character sampling (see below). First, although several archosaur subgroups have been recognised and characterised by synapomorphies their monophyly has not been explicitly tested in a global analysis. Furthermore, many taxa, especially a range of enigmatic crurotarsans called "rauisuchians," are often excluded from analyses, and the choice and construction of characters often masks true morphological variability. In light of these issues, previous authors (e.g. Gower 1999; Nesbitt 2005 have called for restraint in studies of archosaur phylogeny, even going so far as stating that no higher-level analyses should be carried out until the anatomy of basal archosaurs is better described and understood. We believe that the time has come to revisit higher-level archosaur phylogeny in a more complete, detailed, and rigorous light. The past several years have witnessed the discovery of numerous new basal archosaurs (e.g. ). This wealth of new anatomical information has yet to be assimilated into a single analysis. Such an analysis is becoming increasingly necessary, as description and interpretation of new archosaur material is often facilitated by a phylogenetic framework, while quantitative studies of macroevolution, biogeography and extinction demand it. Here we present a new higher-level analysis of crown-group archosaur phylogeny that integrates data from previous analyses, new anatomical information revealed by new discoveries and reinterpretation of taxa, and new characters gleaned from personal observation of specimens. Included are 47 new charaters (25% of the total) and eight taxa 6 that have yet to be included in an analysis, and overall taxonomic sampling is more than double that of any previous study. The result is the largest and most expansive dataset yet applied to archosaur phylogeny, which we use to assess aspects of archosaur history. Additionally, we compare our dataset to previous studies, evaluate the degree of overlap using quantitative metrics, and attempt to pinpoint important sources of disagreement.