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Dryosaurus
''Dryosaurus'' ( ; meaning 'tree lizard', Greek ''δρυς/drys'' meaning 'tree, oak' and ''σαυρος/sauros'' meaning 'lizard'; the name reflects the forested habitat, not a vague oak-leaf shape of its cheek teeth as is sometimes assumed) 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''.〔Galton, P.M., 1977. "The Upper Jurassic dinosaur Dryosaurus and a Laurasia-Gondwana connection in the Upper Jurassic", Nature 268(5617): 230-232〕
==Discovery and naming==
In 1876, Samuel Wendell Williston in Albany County, Wyoming discovered the remains of small euornithopods. In 1878, Professor Othniel Charles Marsh named these as a new species of ''Laosaurus'', ''Laosaurus altus''. The specific name ''altus'', meaning "tall" in Latin, refers to it being larger than ''Laosaurus celer''.〔O.C. Marsh, 1878, "Principal characters of American Jurassic dinosaurs. Part I", ''American Journal of Science and Arts'' 16: 411-416〕 In 1894, Marsh made the taxon a separate genus, ''Dryosaurus''.〔O.C. Marsh, 1894, "The typical Ornithopoda of the American Jurassic", ''American Journal of Science, series 3'' 48: 85-90〕 The generic name is derived from the Greek δρῦς, ''drys'', "tree, oak", referring to a presumed forest-dwelling life mode. Later it was often assumed to have been named after an oak-leaf shape of its cheek teeth, which, however, is absent. The type species remains ''Laosaurus altus'', the ''combinatio nova'' is ''Dryosaurus altus''.
The holotype, YPM 1876, was found in a layer of the Upper Brushy Basin Member of the Morrison Formation, dating from the Tithonian. It consists of a partial skeleton including a rather complete skull and lower jaws. Several other fossils from Wyoming have been referred to ''Dryosaurus altus''. They include specimens YPM 1884: the rear half of a skeleton; AMNH 834: a partial skeleton lacking the skull from the ''Bone Cabin Quarry''; and CM 1949: a rear half of a skeleton dug up in 1905 by William H. Utterback. From 1922 onwards in Utah, Earl Douglass discovered ''Dryosaurus'' remains at the ''Dinosaur National Monument''. These include CM 11340: the front half of a skeleton of a very young individual; CM 3392: a skeleton with skull but lacking the tail; CM 11337: a fragmentary skeleton of a juvenile; and DNM 1016: a left ilium dug up by technician Jim Adams.〔Gilmore C.W., 1925, "Osteology of ornithopodous dinosaurs from the Dinosaur National Monument, Utah. ''Camptosaurus medius'', ''Dryosaurus altus'', ''Laosaurus gracilis''", ''Memoirs of the Carnegie Museum'' 10: 385-409〕 Other fossils were found in Colorado. In Lily Park, Moffat County, James Leroy Kay and Albert C. Lloyd in 1955 recovered CM 21786, a skeleton lacking skull and neck. From Sheetz’ Quarry 1, at Uravan, Montrose County, in 1973 Peter Malcolm Galton and James Alvin Jensen described specimen BYU ESM-171R found by Rodney Dwayne Scheetz and consisting of some vertebrae, a left lower jaw, a left forelimb and two hindlimbs.〔Galton, P.M. & Jensen, J.A., 1973, "Small bones of the hypsilophodontid dinosaur ''Dryoraurus altus'' from the Upper Jurassic of Colorado", ''Great Basin Nature'', 33: 129-132〕 Gregory S. Paul in 2010 suggested that the Utah material represented a separate species.〔Paul, G.S., 2010, ''The Princeton Field Guide to Dinosaurs'', Princeton University Press p. 281〕
Apart from ''Dryosaurus altus'', several other species have been named in the genus. The first of these was created accidentally when in 1903 Giuseppe de Stefano renamed ''Crocodilus phosphaticus'' Thomas 1893 into ''Dryosaurus phosphaticus'';〔G. de Stefano, 1903, "Nuovi rettili degli strati a fosfato della Tunisia", ''Bollettino della Societa Geologica Italiana'' 22: 51-80〕 he had intended to call it ''Dyrosaurus phosphaticus''. This was only emended by Éric Buffetaut in 1981.〔R.T.J. Moody and E. Buffetaut, 1981, "Notes on the systematics and palaeoecology of the crocodiles and turtles of the Metaloui Phosphates (Eocene) of southern Tunisia", ''Tertiary Research'' 3(3): 125-140〕
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