Temporal range: Late Jurassic, 155–145Ma
|D. altus skeleton (front) with Ceratosaurus|
|Species:||† D. altus|
(Marsh, 1878 [originally Laosaurus altus)
Dryosaurus (// DRY-o-SAWR-əs; meaning 'oak lizard', Greek δρυς/drys meaning 'oak' and σαυρος/sauros meaning 'lizard'; the name is from the vague oak-leaf shape of its cheek teeth) 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 were first discovered in the late 19th century. Valdosaurus canaliculatus and Dysalotosaurus lettowvorbecki were both formerly considered to represent species of Dryosaurus.123
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 8 to 14 feet (2.4 to 4.3 m) long and weighed 170 to 200 pounds (77 to 91 kg). However, the adult size is unknown, as no known adult specimens of the genus have been found.4
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.
The teeth of Dryosaurus were, according to museum curator John Foster, characterized by "a strong median ridge on the lateral surface."6Dryosaurus subsisted primarily on low growing vegetation in ancient floodplains.6
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.6 As the animal grew, its eyes became proportionally smaller and its snout proportionally longer.6
The Dryosaurus holotype specimen YPM 1876 was discovered in Reed’s YPM Quarry 5, in the Upper Brushy Basin Member, of the Morrison Formation. In the Late Jurassic Morrison formation of Western North America, Dryosaurus remains have been recovered from stratigraphic zones 2-6.7 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.6
- Tom R. Hübner and Oliver W. M. Rauhut (2010). "A juvenile skull of Dysalotosaurus lettowvorbecki (Ornithischia: Iguanodontia), and implications for cranial ontogeny, phylogeny, and taxonomy in ornithopod dinosaurs". Zoological Journal of the Linnean Society 160 (2): 366–396. doi:10.1111/j.1096-3642.2010.00620.x.
- McDonald AT, Kirkland JI, DeBlieux DD, Madsen SK, Cavin J, et al. (2010). "New Basal Iguanodonts from the Cedar Mountain Formation of Utah and the Evolution of Thumb-Spiked Dinosaurs". In Farke, Andrew Allen. PLoS ONE 5 (11): e14075. doi:10.1371/journal.pone.0014075. PMC 2989904. PMID 21124919.
- Galton, P.M., 1977. "The Upper Jurassic dinosaur Dryosaurus and a Laurasia-Gondwana connection in the Upper Jurassic", Nature 268(5617): 230-232
- Horner, John R.; de Ricqlés, Armand; Padian, Kevin; and Scheetz, Rodney D. (2009). "Comparative long bone histology and growth of the "hysilophodontid" dinosaurs Orodromeus makelai, Dryosaurus altus, and Tenontosaurus tillettii (Ornithischia: Euornithopoda)". Journal of Vertebrate Paleontology 29 (3): 734–747. doi:10.1671/039.029.0312.
- Marshall (1999) pp. 138-139
- "Dryosaurus altus," Foster (2007) pp. 218-219.
- "Appendix," Foster (2007) pp. 327-329.
- Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. 389pp.
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 138–139. ISBN 1-84028-152-9.