Tuesday, November 23, 2010


HADROSAURIDAEThe Hadrosauridae are commonly known as the duck-billed dinosaurs. They first appeared in Medial Cretaceous time and were the last group of ornithopods to evolve. There is more known about this family than any other group of dinosaurs. Their fossil record includes many complete skeletons, eggs and nests, footprints, and two mummified individuals with skin intact (there are also other fossilized skin impressions of these dinosaurs).
The hadrosaruids were large ornithopods, with lengths of 7 to 10 meters. They had broad, toothless beaks and intricate dental batteries. The dental batteries consisted of hundreds of teeth with a washboard-like grinding surface and three replacement teeth in each tooth position. As in the hyspsilophodontids, they had kinetic jaws such that the upper jaw moved outward and the lower jaw moved inward during chewing. They could process fibrous vegetation, even twigs.
Two mummified hadrosaurids from Canada have stomachs full of conifer needles and twigs, seeds, and other tough plant material. There is very little variation among hadrosaurid skelet
Hadrosaurinae skull
ons, so identification is based on skull structure. There are two major subfamilies based on skull type, the Hadrosaurinae and the Lambeosaruinae
The hadrosaurines were the more primitive subfamily with rather flat skull roofs or solid crests on the skull. They were large "Roman-nosed" hadrosaurids with long nasals, which often peaked near the posterior end of the nostrils. Examples are Edmontosaurus and Maisauria.
Lambeosaurinae skull
These were the "crested" duck-bills. They are distinguished by convoluted tubes and crests on the tops of their skulls. The crests contained modified nasal passages and a nasal cavity that was relocated to a position above the orbits. The crests and tubes changed during the growth of individuals, suggesting that sexual dimorphism may have been present. The Upper Cretaceous genera Parasaurolophus and Corythosaurus are representative examples of lambeosaurines.
Short Description
  • Like iguanodontids, hadrosaurids were large, strong, quadrapedal walkers, but also could walk on two legs.

  • Mummies from Alberta have flaps of skin between fingers, has been suggested that they may have had webbed hands; however, the shrunk and stretched skin from mummification may only make it appear that way.

  • They had a tall, paddle-like tail, perhaps for propelling in water.

  • Their skeletons are found in river, lake, swamp, deltaic, and sea depositis. Perhaps they were aquatic dinosaurs. But hadrosaurids were also well suited to living on dry land and thus may have entered the water only for feeding or for defensive purposes.

  • Had a very wide geographic distribution, known from North America, Asia, Europe, and South America. But they were most abundant and diverse in Asia and North America.

  • The hadrosaurids were the dominant plant eating dinosaurs of the Late Cretaceous and they were among the last dinosaurs to become extinct.

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