NEW CLADE OF ENIGMATIC EARLY ARCHOSAURS YIELDS INSIGHTS INTO EARLY PSEUDOSUCHIAN PHYLOGENY AND THE BIOGEOGRAPHY OF THE ARCHOSAUR RADIATION

BUTLER, R. J.; SULLIVAN, C.; EZCURRA, M. D.; LIU, J.; LECUONA, A.; SOOKIAS, R. B.

Berlin

Congreso; 74th Annual Meeting of the Society of Vertebrate Paleontology; 2014

The origin and early evolutionary radiation of archosaurs and their close relatives(Archosauriformes) during the Triassic was a critical event that led to the dinosaurdominatedecosystems of the Jurassic and Cretaceous. The timing and dynamics of thisevolutionary radiation are currently obscured by the poorly constrained phylogeneticpositions of several key early archosauriform taxa, including several species from theMiddle Triassic of Argentina (Gracilisuchus stipanicicorum) and China (Turfanosuchusdabanensis, Yonghesuchus sangbiensis). Morphological phylogenetic analyses of earlyarchosaurs have identified these species as unstable 'wildcards' that reduce phylogeneticresolution. We present new anatomical data for the type specimens of Gracilisuchus,Turfanosuchus, and Yonghesuchus, and incorporate these data into a revised phylogeneticanalysis. Our results indicate that these three previously enigmatic taxa form a wellsupportedclade of Middle Triassic archosaurs that we refer to as Gracilisuchidae, whichis placed basally among suchian archosaurs. The approximately contemporaneous andmorphologically similar Gracilisuchus and Yonghesuchus may be sister taxa withinGracilisuchidae. Our results provide increased resolution of the interrelationships of earlyarchosaurs, with increased levels of phylogenetic support for several key earlypseudosuchian clades. Moreover, they falsify previous hypotheses suggesting thatTurfanosuchus and Yonghesuchus are not members of the archosaur crown group. Therecognition of Gracilisuchidae provides further support for a rapid phylogeneticdiversification of crown archosaurs by the Middle Triassic. The disjunct distribution ofthe gracilisuchid clade in China and Argentina supports the hypothesis that earlyarchosaurs were distributed over much or all of Pangea, although they may have initiallybeen relatively rare members of faunal assemblages.