Dryosaurus (Oak lizard)

Short Info

Dryosaurus (Oak lizard)

Phonetic : Dry-o-sore-us.

Named By : Othniel Charles Marsh – 1894

Diet : Herbivore

Size : Estimated 2-4 meters long

Type of Dinosaur : Euornithopod

Type Species : D. altus (type), D. elderae

Found in : Tanzania, USA, Morrison formation

When it Lived : Late Jurassic, 155-140 million years ago

Dryosaurus (/,draI@’so:r@sDRY-@-SAWR@s) which means “tree lizard”, Greek the word drus (drys) meaning ‘tree’, oak sauros (sauros) meaning lizard and the name refers to the forested environment and not the vague oak-leaf design of its teeth on the cheeks as it is often believed) can be described as a species belonging to ornithopod dinosaurs that was a resident of the Late Jurassic period. It was an Iguanodont (formerly classified as an Hypsilophodont). Fossils were discovered across the Western United States and were first discovered in the 19th century. Valdosaurus canaliculatus as well as Dysalotosaurus lettowvorbecki are both believed to be a the species Dryosaurus.


Beneski Museum of Natural History Dryosaurus altusRichard Haddad, CC BY 2.0, via Wikimedia Commons


Based on the known specimens, it was estimated that they would have been between about 8-14 feet (2.4 to 4.3 millimeters) long, and to weigh as high as 170-200 pounds (77 to 91 kilograms). But because no adult specimens from the genus were found and the size of an adult is unknown. In the year 2018, most massive specimen (CM 1949) was identified as of a different species. Re-examining the identity of this specimen has brought previous studies on growth and size to be questioned.


Dryosaurus limbOthniel Charles Marsh (1831–1899), Public domain, via Wikimedia Commons


Dryosaurus had a neck that was long and slender, long legs, and a long stiff tail. Their arms, however with five fingers per hand, were shorter. They were horny with a beak as well as cheek teeth. There are theories that suggest cheek-shaped structures were present to stop the loss of food as the animal processed it through its mouth. Dryosaurus’ teeth were distinguished by a large median ridge that ran along the lateral surfaces.


Dryosaurus skull dinosaur national monumentJens Lallensack, CC BY-SA 4.0, via Wikimedia Commons


It was in 1876 that Samuel Wendell Williston in Albany County, Wyoming discovered small euornithopods’ remains. In 1878 Professor Othniel Marsh identified them as a distinct species in Laosaurus, Laosaurus altus. Altus meaning “tall” in Latin, is a reference to the fact that it is larger in size than Laosaurus celer. It was in 1894 that Marsh created the taxon as dryosaurus a distinct genus. The name of the generic genus comes from the Greek drys, drus “tree, oak”, in reference to a supposed nature-loving lifestyle. In later times, it was believed to be named in reference to an oak-leaf design of its cheek teeth, but this however, isn’t present. The species that is the type remains Laosaurus altus, and the combinatio nova species is Dryosaurus altus.

The Holotype, YPM 1876, was discovered in a layer of Upper Brushy Basin Member of the Morrison Formation, dating from the Tithonian. It is composed of a part of a skull, which includes a fairly complete skull as well as lower jaws. Other fossils found in Wyoming have been identified as Dryosaurus altus. The most notable are YPM 1884, the rear portion of a skeleton AMNH 834: fragmentary skull that is missing of the Bone Cabin Quarry; and CM 1949: a back portion of a skeleton discovered into during 1905, by William H. Utterback. From 1922 and onwards within Utah, Earl Douglass discovered Dryosaurus remains in the Dinosaur National Monument. They include CM 11340: the front part of a skeleton that belonged to an extremely young person; CM 3392: a skullless skeleton but missing its tail CM 1137, a fragmentary skull from a juvenile as well as DNM 1016: a left ilium that was dug into by technical expert Jim Adams. Additional fossils were discovered in Colorado. At Lily Park, Moffat County, James Leroy Kay and Albert C. Lloyd in 1955 found the skeleton CM 21786, which was without a skull or neck. From the ‘Scheetz’ Quarry 1, at Uravan, Montrose County, in 1973. Peter Malcolm Galton and James Alvin Jensen described the specimen BYU ESM-171R, discovered in the hands of Rodney Dwayne Scheetz and comprising of vertebrae, a lower left jaw, a forelimb on the left as well as two hindlimbs.

Rodney D. Scheetz and his family discovered a fossilized site about five miles away far from Uravan, Colorado in the spring of 1972. The site, accidentally exposed by a bulldozer was found to be a fossilized fragments believed to have been in such good condition they resembled unfossilized bone. The site was described in a 1973 article that was published, and Scheetz continued to explore the site every year until he published the site in a brief note in the year 1991. Around 2500 pieces of material had been discovered and the majority of these were believed to be belonging to Dryosaurus. Eight individuals are depicted, ranging in age from embryonic to juvenile; the discovery of specimens from embryonic stage is extremely rare in dinosaur fossils. Eggshells also were found in the specimen. Scheetz declared his intention to keep working at the site after the publication of the report.

Gregory S. Paul in his field guide to dinosaurs (2nd edition released in 2016) claimed his theory that Utah material could be a separate species. This is verified by Carpenter and Galton (2018) Carpenter and Galton (2018), who identified that the Dinosaur National Monument Dryosaurus as the first species of its kind, D. elderae.

Source: Wikipedia