Ornithopoda (or-nith-uh-PODE-ah) consists of bipedal herbivores with
horny beaks. Larger ornithopods may have walked on all fours when moving
slowly, but like the theropods, they ran with their bodies and tails horizontal
to the ground. This group includes Camptosauridae, Hadrosauridae, Heterodontosauridae,
Hypsilophodontidae and Iguanodontidae.
Heterodontosauridae, a family of ornithopoda, were among the smallest and
earliest ornithischians. These animals had a horny beak, followed by a
large tooth and a row of closely-packed cheek teeth.
One ornithopod provided an important clue to dinosaur behavior. The nests
of Maiasaura were discovered in Montana, along with hatchlings and young
Maiasaura. The conditions of the nests and hatchlings provide evidence
that hadrosaurs -- and probably other dinosaurs -- cared for their young,
something that differentiates them from most modern reptiles. (Maiasaura
means “Good Mother Lizard.”)
Some hadrosaurs had crests upon their heads. Hollow crests served as “resonance
chambers” to project the hadrosaur's calls across great distances. If this
crest was like the inside of a nose, its size would have given the hadrosaur
a very good sense of smell.