GEOL 104 Dinosaurs: A Natural History

Fall Semester 2005
Theropoda I: Dinosaurs red in tooth and claw


  • Name means "beast foot", after the curved claws
  • Characterized by extremely hollow limb bones
  • All, from smallest to largest, were obligate bipeds
  • Became the largest terrestrial carnivores of all time, but began at about 1 m long, and even by end of Late Triassic were dwarfed by rauisuchians

    Some taxa from the Ischigualasto Fm. (Eoraptor and Herrerasauridae) have been considered theropods. Like theropods, they were carnivorous. However, they lack features shared by Sauropodomorpha and Theropoda, and so are most likely non-eusaurischian saurischians.

    True theropods share many derived characters:

    Theropods include three main branches: Coelophysoidea, Ceratosauria, and Tetanurae. Coelophysoids were once considered part of Ceratosauria, but new detailed anatomy suggests that ceratosaurs are closer to tetanurines (in the group Neotheropoda).


    Neotheropoda (ceratosaurs plus tetanurines) appears to be a clade united by several features, such as asymmetrical premaxillary teeth (not cone-shaped as in more primitive forms), fewer maxillary teeth than coelophysoids, modifications of the jaw joint, and a fenestra in the lacrimal leading to hollow chambers.

    Ceratosauria (were called "Neoceratosauria" when coelophysoids were included in Ceratosauria)

    The remaining neotheropods form Tetanurae ("stiff tails"). Tetanurines are characterized by:

    Tetanurines include Spinosauroidea and Avetheropoda. Spinosauriods contain the primitive Megalosauridae (including Megalosaurus) and the highly specialized Spinosauridae.

    Spinosaurids are characterized by:

    The advanced tetanurines form the clade Avetheropoda ("bird theropods"). Avetheropods are characterized by:

    Avetheropoda is divided into two clades, Coelurosauria (subject of the next lecture) and Carnosauria.


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    Last modified: 14 July 2006