Cladogram provided courtesy of T.Holtz Jr. 2004 (


Utahraptor, muscle restoration by Emma Schachner (2004)


>Deinonychus antirrhopus by P. Olsen, based on Paul (1987)

  • These animals had very stiff tails that were used as a counterbalance when running and leaping, they were stiffened by long rods and elongated caudal (tail) vertebrae (long haemal and neural arches)
  • The second toe of each foot had an enlarged sickle claw that is hypothesised to have been retractable and used in a slashing mode for attacking prey
  • The legs were shorter and stockier than other theropods
  • There has been fossil evidence that these predators hunted in packs
  • They have been found throughout the Cretaceous in North American, Europe, and Asia (effectively Laurasia)
  • Examples : Deinonychus antirrhopus, Velociraptor mongoliensis

Sinovenator changii by Todd Marshall (2004)


  • Troodontids had shorter arms than dromaeosaurids
  • The legs were thin and long, with an arctometatarsus
  • The teeth were leaf-shaped indicating possible omnivory
  • They had the largest brain case of any other dinosaur
  • Enlarged sickle claw on second toe
  • Common from the Middle Jurassic through the Cretaceous

Troodon formosus by Todd Marshall (2004)


Archaeopteryx lithographica by Todd Marshall (2004)

Rahonavis ostromii by Todd Marshall (2004)

This group encompases all other birds, extinct and still living. They have traits such as a pygostyle, strutlike coracoid, and a toothless beak that differentiate them from their ancestors


Author: Emma Schachner
Last updated: 13 November 2004
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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2003-4