Cast skeleton of Heterodontosaurus tucki, copyright Daderot.

Belongs within: Ornithodira.
Contains: Sauropodomorpha, Theropoda, Genasauria.

As the clade containing the largest land animals of the Mesozoic (and indeed of all time), the Dinosauria hardly need introduction. The most significant feature of the clade was the development of a fully upright stance, so the legs were positioned directly underneath the body. The basal division of the dinosaurs into the Saurischia (containing theropods and sauropodomorphs) and Ornithischia (containing ornithopods, marginocephalians, stegosaurs and ankylosaurs) has been almost universally accepted has recently been challenged by Baron et al. (2017) who found theropods and ornithischians to form a clade to the exclusion of sauropodomorphs. The position of the basal Herrerasauridae, carnivorous taxa from the Late Triassic of North and South America, has been subject to some shuffling, with various authors placing them as either basal theropods, basal sauropodomorphs or basal saurischians outside a Theropoda + Sauropodomorpha clade.

The earliest known representative of the Ornithischia is Pisanosaurus mertii from the Late Triassic (Carnian) of Argentina, and many analyses have placed this species as the basalmost member of the clade. The Heterodontosauridae are a group of small bipedal ornithischians known from the Jurassic and Early Cretaceous, characterised by the enlargement of one or more pairs of teeth near the front of the jaw into canine-like tusks.

See also: The top ten dinosaurs—Triceratops beats Tyrannosaurus; Top ten follow-up; Dinosaurs all over the place; A question of availability.

Synapomorphies (from Juul 1994): Increased asymmetry of hands, with fewer phalanges in outer digits; semiperforate acetabulum, prominent supra-acetabular buttress; proximal head on femur fully offset, with distinct ball and neck; ischium with slender shaft, ventral keel restricted to proximal third; tibia anteroproximally and posteriorly overlapping ascending process of astragalus, posterior process of tibia projecting ventrally; calcaneum with concave proximal articular surface.

<==Dinosauria [Eudinosauria, Eusaurischia, Phytodinosauria]
    |  i. s.: Teyuwasu barberenai Kischlat 1999 (n. d.) L04
    |         Thecospondylus horneri Seeley 1882 (n. d.) L04
    |         Spinosuchus R72
    |--Saurischia BNB17
    |    |--Sauropodomorpha BNB17
    |    `--Herrerasauridae [Herrerasauria, Herreravia] BNB17
    |         |  i. s.: Aliwalia Galton 1985 P88, L04
    |         |           `--A. rex Galton 1985 L04
    |         |         Alwalkeria Chatterjee & Creisler 1994 L04 [=Walkeria Chatterjee 1986 P88, L04]
    |         |           `--A. maleriensis (Chatterjee 1986) [=Walkeria maleriensis] L04
    |         |--Staurikosaurus Colbert 1970 NS09, L04
    |         |    `--S. pricei Colbert 1970 L04
    |         `--+--+--Chindesaurus Long & Murry 1995 NS09, L04 [incl. Caseosaurus Hunt, Lucas et al. 1998 L04]
    |            |  |    `--C. bryansmalli Long & Murry 1995 [incl. Caseosaurus crosbyensis Hunt, Lucas et al. 1998] L04
    |            |  `--Sanjuansaurus gordilloi BNB17
    |            `--Herrerasaurus Reig 1963 NS09, L04 [incl. Frenguellisaurus Novas 1986 L04, Ischisaurus Reig 1963 L04]
    |                 `--H. ischigualastensis Reig 1963 (see below for synonymy) L04
    `--Ornithoscelida BNB17
         |--Theropoda BNB17
         `--Ornithischia [Fabrosauridae, Heterodontosauriformes] BNB17
              |  i. s.: Fabrosaurus australis Ginsburg 1964 (n. d.) NWW04
              |         Nanosaurus agilis Marsh 1877 (n. d.) NS04
              |         Alocodon Thulborn 1973 NWW04, D07
              |           `--A. kuehnei Thulborn 1973 (n. d.) NWW04
              |         Trimucrodon cuneatus Thulborn 1973 (n. d.) NWW04
              |         Lucianosaurus wildi Hunt & Lucas 1994 (n. d.) NWW04
              |         Pekinosaurus olseni Hunt & Lucas 1994 (n. d.) NWW04
              |         Taveirosaurus costai Antunes & Sigogneau-Russell 1991 (n. d.) NWW04
              |         Galtonia Hunt & Lucas 1994 non Decaisne 1880 (ICBN) NWW04
              |           `--*G. gibbidens (Cope 1878) [=Thecodontosaurus gibbidens] NWW04
              |         Xiaosaurus Dong & Tang 1983 NWW04, D07
              |           `--X. dashanpensis Dong & Tang 1983 (n. d.) NWW04
              |         Dianchungosaurus lufengensis Young 1982 (n. d.) NS04
              |         Laosaurus NS04
              |           |--L. celer Marsh 1878 (n. d.) NS04
              |           `--L. minimus Gilmore 1924 (n. d.) NS04
              |         Phyllodon henkeli Thulborn 1973 (n. d.) NS04
              |         Siluosaurus zhangquiani Dong 1997 (n. d.) NS04
              |--Pisanosaurus Casamiquela 1967 BNB17, NWW04
              |    `--P. mertii Casamiquela 1967 NWW04
              `--+--+--Genasauria BNB17
                 |  `--Eocursor Butler, Smith & Norman 2007 BSN07
                 |       `--*E. parvus Butler, Smith & Norman 2007 BSN07
                 `--Heterodontosauridae BSN07
                      |  i. s.: Geranosaurus atavus Broom 1911 (n. d.) N85, NS04
                      |         Lycorhinus Haughton 1924 [incl. Lanasaurus Gow 1975] NS04
                      |           `--L. angustidens Haughton 1924 [incl. Lanasaurus scalpridens Gow 1975] NS04
                      |         Echinodon Owen 1861 NS04
                      |           `--E. becklesii Owen 1861 NS04
                      |--Tianyulong Zheng, You et al. 2009 BNB17, ZY09
                      |    `--*T. confuciusi Zheng, You et al. 2009 ZY09
                      `--+--Fruitadens haagarorum BNB17
                         `--+--Manidens condorensis BNB17
                            |--Abrictosaurus Hopson 1975 BNB17, NS04
                            |    `--A. consors (Thulborn 1974) [=Lycorhinus consors] NS04
                            `--Heterodontosaurus Crompton & Charig 1962 BNB17, NS04
                                 `--H. tucki Crompton & Charig 1962 NS04

Herrerasaurus ischigualastensis Reig 1963 [incl. Ischisaurus cattoi Reig 1963, Frenguellisaurus ischigualastensis Novas 1986 non H. ischigualastensis Reig 1963] L04

*Type species of generic name indicated


[BNB17] Baron, M. G., D. B. Norman & P. M. Barrett. 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543: 501–506.

[BSN07] Butler, R. J., R. M. H. Smith & D. B. Norman. 2007. A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia. Proceedings of the Royal Society of London Series B—Biological Sciences 274 (1621): 2041–2046.

[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.

Juul, L. 1994. The phylogeny of basal archosaurs. Palaeontologia Africana 31: 1-38.

[L04] Langer, M. C. 2004. Basal Saurischia. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 25–46. University of California Press: Berkeley.

[NS09] Nesbitt, S. J., N. D. Smith, R. B. Irmis, A. H. Turner, A. Downs & M. A. Norell. 2009. A complete skeleton of a Late Triassic saurischian and the early evolution of dinosaurs. Science 326: 1530–1533.

[N85] Norman, D. 1985 (reprinted 2000). The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

[NS04] Norman, D. B., H.-D. Sues, L. M. Witmer & R. A. Coria. 2004. Basal Ornithopoda. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 393–412. University of California Press: Berkeley.

[NWW04] Norman, D. B., L. M. Witmer & D. B. Weishampel. 2004. Basal Ornithischia. In: Weishampel, D. B., P. Dodson & H. Osmólska (eds) The Dinosauria 2nd ed. pp. 325–334. University of California Press: Berkeley.

[P88] Paul, G. S. 1988. Predatory Dinosaurs of the World: A Complete Illustrated Guide. Simon & Schuster: New York.

[R72] Romer, A. S. 1972. The Chañares (Argentina) Triassic reptile fauna. XVI. Thecodont classification. Breviora 395: 1–24.

[ZY09] Zheng, X.-T., H.-L. You, X. Xu & Z.-M. Dong. 2009. An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures. Nature 458: 333–336.

Last updated: 6 August 2017.

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