The earliest bird-line archosaurs and the assembly of the dinosaur body plan

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The relationship between dinosaurs and other reptiles is well established1,2,3,4, but the sequence of acquisition of dinosaurian features has been obscured by the scarcity of fossils with transitional morphologies. The closest extinct relatives of dinosaurs either have highly derived morphologies5,6,7 or are known from poorly preserved8,9 or incomplete material10,11. Here we describe one of the stratigraphically lowest and phylogenetically earliest members of the avian stem lineage (Avemetatarsalia), Teleocrater rhadinus gen. et sp. nov., from the Middle Triassic epoch. The anatomy of T. rhadinus provides key information that unites several enigmatic taxa from across Pangaea into a previously unrecognized clade, Aphanosauria. This clade is the sister taxon of Ornithodira (pterosaurs and birds) and shortens the ghost lineage inferred at the base of Avemetatarsalia. We demonstrate that several anatomical features long thought to characterize Dinosauria and dinosauriforms evolved much earlier, soon after the bird–crocodylian split, and that the earliest avemetatarsalians retained the crocodylian-like ankle morphology and hindlimb proportions of stem archosaurs and early pseudosuchians. Early avemetatarsalians were substantially more species-rich, widely geographically distributed and morphologically diverse than previously recognized. Moreover, several early dinosauromorphs that were previously used as models to understand dinosaur origins may represent specialized forms rather than the ancestral avemetatarsalian morphology.

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We acknowledge A. Tibaijuka for help with fieldwork logistics in Tanzania. Supported by National Geographic Society Research & Exploration grant (9606-14, S.J.N.), National Science Foundation EAR-1337569 (C.A.S.) and EAR-1337291 (K.D.A., S.J.N.), a Marie Curie Career Integration Grant (630123, R.J.B.), a National Geographic Society Young Explorers grant (9467-14 M.D.E.), and the Russian Government Program of Competitive Growth of Kazan Federal University and RFBR 14-04-00185, 17-04-00410 (A.G.S.). We thank S. Chapman, A. C. Milner, M. Lowe and S. Bandyopadhyay for access to specimens, S. Werning, G. Lloyd, R. Close and K. Padian for discussions, and H. Taylor for photographs of the holotype.

Author information

Author notes

    • Alan J. Charig



  1. Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA

    • Sterling J. Nesbitt
    •  & Michelle R. Stocker
  2. School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK

    • Richard J. Butler
    •  & Martín D. Ezcurra
  3. CONICET—Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina

    • Martín D. Ezcurra
  4. Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK

    • Paul M. Barrett
    •  & Alan J. Charig
  5. Integrative Research Center, Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA

    • Kenneth D. Angielczyk
  6. Evolutionary Studies Institute, University of the Witwatersrand, PO Wits 2050, Johannesburg, South Africa

    • Roger M. H. Smith
  7. Iziko South African Museum, PO Box 61, Cape Town, South Africa

    • Roger M. H. Smith
  8. Burke Museum and Department of Biology, University of Washington, Seattle, Washington 98195, USA

    • Christian A. Sidor
  9. Department of Organismal Biology, Uppsala University, Norbyvägen 18A, 752 36 Uppsala, Sweden

    • Grzegorz Niedźwiedzki
  10. Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya 123, Moscow 117997, Russia

    • Andrey G. Sennikov
  11. Kazan Federal University, Kremlyovskaya ul. 18, Kazan 420008, Russia

    • Andrey G. Sennikov


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S.J.N., R.J.B., M.D.E. and P.M.B. designed the research project; C.A.S. and K.D.A. designed the field project; S.J.N., C.A.S., K.D.A., R.M.H.S. and M.R.S. conducted fieldwork; S.J.N., R.J.B., M.D.E., P.M.B., M.R.S. and A.J.C. described the material; S.J.N., M.D.E. and M.R.S. conducted the phylogenetic analyses; R.J.B. conducted disparity analyses; and S.J.N., R.J.B., M.D.E., P.M.B., M.R.S., K.D.A., R.M.H.S., C.A.S., G.N. and A.G.S. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sterling J. Nesbitt.

Reviewer Information Nature thanks K. Padian and H.-D. Sues for their contribution to the peer review of this work.

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