Ornithopoda

HETERODONTOSAURIDAE

  • The most primitive of the ornithopods
  • Ranged in age from the Late Triassic (extremely rare) to the Late Jurassic
  • Bipedal with functional grasping hands
  • Robust jaws with various kinds of teeth, ranging from canine fangs to backwards-pointing chisel-shaped teeth
  • Teeth were often present on the premaxilla (bone at the end of the snout)
  • May be the basal ornithopods, or may be closer to marginocephalians
  • Example: Heterodontosaurus

Cladogram courtesy of T. Holtz Jr. 2004 (http://www.geol.umd.edu/~tholtz/G104/10419orni.htm)

HYPSILOPHODONTS


Iguanodon by Todd Marshall (2004)

IGUANODONTIA

  • These animals were much larger than the more basal ornithopods
  • Their forelimbs were used for walking and grasping, so they were partially bipedal
  • The premaxillary teeth have been lost
  • The external nares were much larger, and had fleshy components in some forms
  • Originated during the Middle Jurassic, but became extremely common during the Cretaceous

    Cladogram courtesy of T. Holtz Jr. 2004 (http://www.geol.umd.edu/~tholtz/G104/10419orni.htm)

HADROSAURIFORMES

  • The hadrosauriforms were larger and more specialized than the basal iguanodonts
  • The grew to lengths of 14 metres
  • The hand became more specialized, with the thumb bones fused into a spike, an opposable fourth finger, and a hoof-like two middle fingers
  • The jaws and teeth were highly efficient grinding machines with a hinge between the jaw and skull allowing a 'chewing' mechanism, and rows of hundreds of teeth in the back of the jaw
  • Example: Iguanodon

Iguanodon family by Todd Marshall (2004)

Hadrosaurids by John Sibbick (2004)
HADROSAURIDS "duck-billed dinosaurs"(2)

CHARACTERS

  1. HADROSAURINAE

    • These hadrosaurids had very wide faces with large nostrils
    • They possesed no cranial ornamentation
    • Examples: Edmontosaurus, Hadrosaurus foulkii
  2. LAMBEOSAURINAE

    • The lambeosaurs had various cranial ornaments that were hollow and developed late in life
  • Palaeontologists have speculated that hadosaur head crests were used for communication, sexual dimorphism, visual display, and breathing
  • Examples: Parasaurolophus, Lambeosaurus, Corythosaurus

Different Hadrosaurid skull types (Benton, 2000)


Parasaurolophus by P. Olsen (2004)


NEXT: MARGINOCEPHALIA



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