EXPLORING THE EARLY MACROEVOLUTIONARY HISTORY OF PERMOTRIASSIC ARCHOSAUROMORPHS THROUGH A COMPREHENSIVE PHYLOGENETIC DATASET

EZCURRA, M. D.

Congreso; XXV Congreso Brasileiro de Paleontologia Resumos; 2017

The early evolution of archosauromorphsduring the Permo-Triassic (~270−200 Ma)represents a case of study of anevolutionary radiation in deep time and thebiotic recovery after a mass extinction.However, macroevolutionary studies ofearly archosauromorphs have beenhistorically limited by poor knowledge oftheir phylogenetic relationships. Aphylogenetic matrix composed of 114terminals and 685 osteological characterswas assembled and analysed toreconstruct the higher-level relationships ofbasal archosauromorphs. The results ofthe cladistic analysis include a polyphyletic"Prolacertiformes", "Protorosauria", and"Proterosuchia". Prolacertids, rhynchosaurs,allokotosaurians, and tanystropheidsare the major successive sister clades,respectively, of Archosauriformes. WithinAllokotosauria, the Indian Pamelaria isrecovered as an azendohsaurid and a new,relatively large-sized species withsupraorbital horns from India is found asthe sister-taxon of Azendohsaurus.Proterosuchidae is unambiguouslyrestricted to six species that occurimmediately after and before the Permo-Triassic boundary and represent a shortlived"disaster-clade". Other putativeproterosuchids are found as nonarchosauriformarchosauromorphs, earlyarchosauriforms, or even crown-archosaurs.Erythrosuchidae is found as amonophyletic group composed of eightEarly and Middle Triassic species. Theprobable semi-aquatic doswelliids andproterochampsids are more closely relatedto each other than to other archosauromorphs.Erpetosuchids are found asnon-suchian pseudosuchians, includingspecies from South and North America,Africa, and Europe. The recently erectedAphanosauria includes Middle to early LateTriassic species and are the earliestbranching members of the avian lineage ofarchosaurs and show a transitionalcombination of characters between nonarchosaurianarchosauriforms and ornithodirans.This phylogenetic data matrix wasused to explore quantitatively morphologicaldisparity and evolutionary ratesthrough time. The results indicate thatarchosauromorphs underwent a majorphylogenetic diversification in theOlenekian (~251−247 Ma), characterisedby significantly elevated evolutionary rates.The Anisian (~247−242 Ma) ischaracterised by conspicuous increases inobserved species richness, abundance,and disparity. This coincides with the endof an interval of highly fluctuating globaltemperatures after the Permo-Triassicmass extinction and an increase of plantdiversity, suggesting the recovery andstabilization of global ecosystems. Thismultiphase early evolutionary radiation ofarchosauromorphs set the beginning oftheir dominance in terrestrial ecosystemsthrough the rest of the Mesozoic.