Dawn of the Dinosaurs: Archosauromorph Evolution in the Terrestrial Triassic
Final Report Abstract
The Triassic Period (252–200 million years ago) was a critical phase of Earth history, which saw major changes amongst vertebrate communities on land. These changes laid the foundations of modern ecosystems, and have been dubbed “The Great Transition”. The Archosauromorpha, a highly diverse group of reptiles (including dinosaurs, pterosaurs, crocodiles and birds), diversified, subsequently dominating land-living communities for the remainder of the Mesozoic (~200–65 million years ago). Understanding the early archosauromorph radiation is fundamental to understanding the rise of dinosaurian communities, but scientific progress in this area has been hampered by poor understanding of the anatomy, taxonomy and phylogeny of most early archosauromorph groups, and the fact that the diversification and biogeography of early archosauromorphs have only rarely been examined using quantitative approaches. In this project, we carried out extensive specimen-based revisions of key taxa of early archosauromorphs dating from the Permian to earliest Jurassic, based on first-hand examination of fossil material in collections worldwide and imaging techniques such as CT scanning. This research has allowed us to clarify the taxonomy, diversity and temporal and spatial distributions of key groups of early archosauromorphs, including early rhynchosaurs, proterosuchids, erythrosuchids, euparkeriids, early phytosaurs, and early crown group archosaurs. It has also provided large volumes of new anatomical data, and novel information on early archosauromorph growth and palaeobiology. Our greatly improved understanding of early archosauromorph anatomy and taxonomy has underpinned detailed quantitative phylogenetic work at multiple scales, ranging from understanding the relationships between major archosauromorph clades, to clarifying the taxonomic content and relationships within individual clades. For example, our work has clarified the taxonomic content of the latest Permian–earliest Triassic clade Proterosuchidae, showing that it includes species from Russia, South Africa, China and India, but excludes some species previously referred to it, such as Tasmaniosaurus from Australia. Our work has clarified the timing and patterns of the early archosauromorph radiation. It demonstrates that archosauromorphs originated probably during the middle Permian, and underwent a substantial global diversification in the late Permian, which is poorly represented in the fossil record. Archosauromorphs increased dramatically in diversity after the Permian–Triassic mass extinction, with a substantial increase in species richness in the earliest Triassic dominated by the short-lived disaster taxon Proterosuchidae. Increases in morphological diversity and body size were delayed relative to increases in species richness, with a major change occurring around the Early–Middle Triassic boundary, coincident with a stabilisation of global communities following the mass extinction. Ongoing and future research is aimed at quantifying these qualitative patterns, in order to further illuminate the dawn of the Mesozoic Era.
Publications
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2014. New clade of enigmatic early archosaurs yields insights into early pseudosuchian phylogeny and the biogeography of the archosaur radiation. BMC Evolutionary Biology 14:128
Butler RJ, Sullivan C, Ezcurra MD, Liu J, Lecuona A, Sookias RB
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2014. Redescription of the phytosaurs Paleorhinus ("Francosuchus") angustifrons and Ebrachosuchus neukami from Germany, with implications for Late Triassic biochronology. Zoological Journal of the Linnean Society 170: 155–208
Butler RJ, Rauhut OWM, Stocker MR, Bronowicz, R
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2014. Systematics of putative euparkeriids (Diapsida: Archosauriformes) from the Triassic of China. PeerJ 2:e658
Sookias RB, Sullivan C, Liu J, Butler RJ
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2014. The monophyly of Euparkeriidae (Reptilia: Archosauriformes) and the origins of crown Archosauria: a revision of Dorosuchus neoetus from the Middle Triassic of Russia. Palaeontology 57:1177–1202
Sookias RB, Sennikov AG, Gower DJ, Butler RJ
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2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLOS ONE 9: e89165
Ezcurra MD, Scheyer T, Butler RJ
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2015. Post-hatchling cranial ontogeny in the Early Triassic diapsid reptile Proterosuchus fergusi. Journal of Anatomy 226:387–402
Ezcurra MD, Butler RJ
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2015. Systematics and evolutionary history of proterosuchian archosauriforms. PhD thesis, University of Birmingham
Ezcurra MD
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2015. Taxonomy of the proterosuchid archosauriforms (Diapsida: Archosauromorpha) from the earliest Triassic of South Africa, and implications for the early archosauriform radiation. Palaeontology 58:141–170
Ezcurra MD, Butler RJ
