Ornithopoda

• 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

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

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