Article | Published:

A new hypothesis of dinosaur relationships and early dinosaur evolution

Nature volume 543, pages 501506 (23 March 2017) | Download Citation


For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.

  • Subscribe to Nature for full access:



Additional access options:

Already a subscriber?  Log in  now or  Register  for online access.


  1. 1.

    et al. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464, 95–98 (2010)

  2. 2.

    A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny. J. Syst. Palaeontol. 8, 371–425 (2010)

  3. 3.

    On the classification of the fossil animals commonly named Dinosauria. Proc. R. Soc. Lond. 43, 165–171 (1887)

  4. 4.

    Osteology of the Reptiles. (Univ. Chicago Press, 1956)

  5. 5.

    , & On the origin of the sauropods and the classification of the Saurischia. Proc. Linnean Soc. Lond. 176, 197–221 (1965)

  6. 6.

    & Dinosaur monophyly and a new class of vertebrates. Nature 248, 168–172 (1974)

  7. 7.

    In The Origin of Birds and the Evolution of Flight (ed. ) Ch. 8, 1–55 (Memoir California Academy of Science, 1986)

  8. 8.

    A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs. J. Syst. Palaeontol. 1, 1–42 (2003)

  9. 9.

    & Early dinosaurs: a phylogenetic study. J. Syst. Palaeontol. 4, 309–358 (2006)

  10. 10.

    Solving a dinosaurian puzzle: the identity of Aliwalia rex Galton. Hist. Biol. 19, 93–123 (2007)

  11. 11.

    et al. A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326, 1530–1533 (2009)

  12. 12.

    , , & A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proc. R. Soc. B 278, 3459–3464 (2011)

  13. 13.

    The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352 (2011)

  14. 14.

    The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth Environ. Sci. Trans. R. Soc. Edinburgh 103, 423–442 (2013)

  15. 15.

    Notes on the postcranial anatomy of the heterodontosaurid dinosaur Heterodontosaurus tucki, a basal ornithischian from the Lower Jurassic of South Africa. Rev. Paleobiol. 33, 97–141 (2014)

  16. 16.

    , , , & The Lower Jurassic ornithischian dinosaur Heterodontosaurus tucki Crompton & Charig, 1962: cranial anatomy, functional morphology, taxonomy, and relationships. Zool. J. Linn. Soc. 163, 182–276 (2011)

  17. 17.

    , & TNT, a free program for phylogenetic analysis. Cladistics 24, 774–786 (2008)

  18. 18.

    On the classification of the Dinosauria with observations on the Dinosauria of the Trias. Q. J. Geol. Soc. 26, 32–51 (1870)

  19. 19.

    , & A new early Late Triassic saurischian dinosaur from Rio Grande do Sol state, Brazil. Proc. 2nd Gondwanan Dinosaur Symposium, 15, 89–109 (National Science Museum Monographs, 1999)

  20. 20.

    The pelvic and hind limb anatomy of the stem-sauropodomorph Saturnalia tupiniquim (Late Triassic, Brazil). PaleoBios 23, 1–30 (2003)

  21. 21.

    et al. New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil. Naturwissenschaften 98, 1035–1040 (2011)

  22. 22.

    , & Osteology of Eoraptor lunensis (Dinosauria, Sauropodomorpha). J. Vert. Paleontol. Memoir 12, 83–179 (2013)

  23. 23.

    , & Postcranial anatomy of Lesothosaurus diagnosticus (Dinosauria: Ornithischia) from the Lower Jurassic of southern Africa: implications for basal ornithischian taxonomy and systematics. Zool. J. Linn. Soc. 179, 125–168 (2017)

  24. 24.

    A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zool. J. Linn. Soc. 158, 882–935 (2010)

  25. 25.

    Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. ZooKeys 226, 1–225 (2012)

  26. 26.

    , & (eds) The Dinosauria 2nd edn (Univ. California Press, 2004)

  27. 27.

    Report on British fossil reptiles. Part II. Rep. British Assoc. Adv. Sci. 11, 60–204 (1842)

  28. 28.

    The logical basis of phylogenetic taxonomy. Syst. Biol. 54, 595–619 (2005)

  29. 29.

    , & Dinosaur diversity and the rock record. Proc. R. Soc. B 276, 2667–2674 (2009)

  30. 30.

    Principal characters of American Jurassic dinosaurs V. Am. J. Sci. 16, 411–416 (1881)

  31. 31.

    , , , & In Phylonyms: a Companion to the PhyloCode (eds , , ) (Univ. California Press, 2010)

  32. 32.

    et al. The origin and early radiation of dinosaurs. Earth Sci. Rev. 101, 68–100 (2010)

  33. 33.

    , & A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia. Proc. R. Soc. B 274, 2041–2046 (2007)

  34. 34.

    , & The phylogeny of ornithischian dinosaurs. J. Syst. Palaeont. 6, 1–40 (2008)

  35. 35.

    , & The roles of herbivory and omnivory in early dinosaur evolution. Earth Environ. Sci. Trans. R. Soc. Edinburgh 101, 383–396 (2010)

  36. 36.

    , , & Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer (Chañares Formation, Argentina), its inclusivity, and relationships amongst early dinosauromorphs. J. Syst. Palaeont. 13, 189–219 (2015)

  37. 37.

    Phylogenetic relationships of the basal dinosaurs, the Herrerasauridae. Palaeontology 35, 51–62 (1992)

Download references


We thank S. Chapman (Natural History Museum, London, UK), R. Smith (Iziko South African Museum, Cape Town, South Africa), E. Butler (National Museum, Bloemfontein, South Africa) B. Zipfel (Bernard Price Institute for Palaeontological Research, Johannesburg, South Africa), J. Powell (Instituto Miguel Lillo, Tucumán, Argentina), R. Martinez (Museo de Ciencias Naturales, San Juan, Argentina) and D. Pol (Museo Paleontológico Egidio Feruglio, Trelew, Argentina) for access to specimens in their care, R. Butler, J. Choiniere, B. McPhee, C. VanBuren and K. Chapelle for helpful discussion, M. Williams for assisting with the production of figures, and C. Baron for helpful comments on the manuscript, and the Willi Hennig Society for making TNT 1.5-beta software freely available. Funding for M.G.B. was provided by a NERC/CASE Doctoral Studentship (NE/L501578/1).

Author information


  1. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK

    • Matthew G. Baron
    •  & David B. Norman
  2. Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK

    • Matthew G. Baron
    •  & Paul M. Barrett


  1. Search for Matthew G. Baron in:

  2. Search for David B. Norman in:

  3. Search for Paul M. Barrett in:


M.G.B., P.M.B. and D.B.N. designed this research project. M.G.B., D.B.N. and P.M.B. contributed data. M.G.B. conducted the phylogenetic analyses. M.G.B, D.B.N. and P.M.B. wrote the manuscript. M.G.B. and D.B.N. produced the figures.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Matthew G. Baron.

Reviewer Information Nature thanks K. Padian, H.-D. Sues and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    This file contains Supplementary Text and Data, Supplementary Tables 1-3 and additional references.

About this article

Publication history





Rights and permissions

To obtain permission to re-use content from this article visit RightsLink.


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.