The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms

EZCURRA, M. D.

PeerJ

PeerJ

Año: 2016 vol. 4

The early evolution of archosauromorphs during the Permo-Triassic constitutes anexcellent empirical case study to shed light on evolutionary radiations in deep timeand the timing and processes of recovery of terrestrial faunas after a mass extinction.However, macroevolutionary studies of early archosauromorphs are currentlylimited by poor knowledge of their phylogenetic relationships. In particular, oneof the main early archosauromorph groups that need an exhaustive phylogeneticstudy is ``Proterosuchia,´´ which as historically conceived includes members of bothProterosuchidae and Erythrosuchidae. A new data matrix composed of 96 separatetaxa (several of them not included in a quantitative phylogenetic analysis before) and600 osteological characters was assembled and analysed to generate a comprehensivehigher-level phylogenetic hypothesis of basal archosauromorphs and shed light onthe species-level interrelationships of taxa historically identified as proterosuchianarchosauriforms. The results of the analysis using maximum parsimony include apolyphyletic ``Prolacertiformes´´ and ``Protorosauria,´´ in which the Permian Aenigmastropheusand Protorosaurus are the most basal archosauromorphs. The enigmaticchoristoderans are either found as the sister-taxa of all other lepidosauromorphs orarchosauromorphs, but consistently placed within Sauria. Prolacertids, rhynchosaurs,allokotosaurians and tanystropheids are the major successive sister clades of Archosauriformes.The Early Triassic Tasmaniosaurus is recovered as the sister-taxonof Archosauriformes. Proterosuchidae is unambiguosly restricted to five species thatoccur immediately after and before the Permo-Triassic boundary, thus implyingthat they are a short-lived ``disaster´´ clade. Erythrosuchidae is composed of eightnominal species that occur during the Early and Middle Triassic. ``Proterosuchia´´ ispolyphyletic, in which erythrosuchids are more closely related to Euparkeria and morecrownward archosauriforms than to proterosuchids, and several species are foundwidespread along the archosauromorph tree, some being nested within Archosauria(e.g., ``Chasmatosaurus ultimus,´´ Youngosuchus). Doswelliids and proterochampsidsare recovered as more closely related to each other than to other archosauromorphs,forming a large clade (Proterochampsia) of semi-aquatic to aquatic forms that includesthe bizarre genus Vancleavea. Euparkeria is one of the sister-taxa of the clade composedof proterochampsians and archosaurs. The putative Indian archosaur Yarasuchus isrecovered in a polytomy with Euparkeria and more crownward archosauriforms, and as more closely related to the Russian Dongusuchus than to other species. Phytosaursare recovered as the sister-taxa of all other pseudosuchians, thus being nested withinArchosauria.