Dryosaurus ( ; meaning 'oak lizard', due to the vague oak shape of its cheek teeth (Greek δρυο/dryo meaning 'oak' and σαυρος/sauros meaning 'lizard') is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont (formerly classified as a hypsilophodont). Fossils have been found in the western United States and Tanzania and were first discovered in the late 19th century. The Tanzanian site proved to be an especially fertile hunting ground for Dryosaurus fossils, this specimen was previously called Dysalotosaurus (meaning "lost wood reptile"). An expedition led by German paleontologist Werner Janensch found a great many fossils that represented Dryosaurus at many stages of development.

Paleobiology

Dryosaurus had a long neck, long, slender legs and a long, stiff tail. Its 'arms', however, with five 'fingers' on each 'hand', were short. Known specimens were about long and weighed . However, the adult size is unknown, as no known adult specimens of the genus have been found.

Dryosaurus had a horny beak and cheek teeth and, like other ornithopods, was a herbivore. Some scientists suggest that it had cheek-like structures to prevent the loss of food while the animal processed it in the mouth.

A quick and agile runner with strong legs, Dryosaurus used its stiff tail as a counter-balance. It probably relied on its speed as a main defense against carnivorous dinosaurs.

Diet and dentition

Dryosaurus from the Morrison Formation subsisted primarily on low growing vegetation in the ancient floodplain.

Othnielosaurus was a dinosaur genus contemporary to Dryosaurus, although smaller and with more primitive dentition. The more highly derived teeth of Dryosaurus were, according to museum curator John Foster, characterized by "a strong median ridge on the lateral surface."

Growth and development

D. lettowvorbecki exhibited high rates of growth that were both continuous and independent of seasonal weather variation.

A Dryosaurus hatchling found at Dinosaur National Monument in Utah confirmed that Dryosaurus followed similar patterns of craniofacial development to other vertebrates; the eyes were proportionally large while young and the muzzle proportionally short. As the animal grew it's eyes became proportionally smaller and its snout proportionally longer.

Species

D. altus (previously Laosaurus altus)

Dryosaurus altus was originally described as Laosaurus altus.

D. lettowvorbecki (previously Dysalotosaurus lettowvorbecki)

The African Dryosaurus, D. lettowvorbecki, was originally described as the type species of a separate genus called Dysalotosaurus.

Paleobiogeography and fossil distribution

Morrison Formation

In the Late Jurassic Morrison formation of Western North America, Dryosaurus remains have been recovered from stratigraphic zones 2-6. A spectacular digsite near Uravan, Colorado held hundreds of D. altus fossils which represented multiple stages of the animal's life cycle. Other sites that have produced Dryosaurus material include Bone Cabin Quarry, the Red Fork of the Powder River in Wyoming and Lily Park in Colorado.

See also

• List of dinosaurs
• Paleobiota of the Morrison Formation
• Othnielosaurus, an anatomically similar, although somewhat smaller animal.

External links

• Dryosaurus, from the Dinosaur Encyclopaedia at Univ. of Illinois at Urbana-Champagne
• http://www.thescelosaurus.com/iguanodontia.htm

Footnotes

1. Marshall (1999) pp. 138-139
2. "Dryosaurus altus," Foster (2007) pp. 218-219.
3. "Appendix," Foster (2007) pp. 327-329.

References

• Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp.