[citation needed] Some scientists suggest that it had cheek-like structures to prevent the loss of food while the animal processed it in the mouth.[who?]

[9] The generic name is derived from the Greek δρῦς, drys, "tree, oak", referring to a presumed forest-dwelling life mode.

[9] The holotype, YPM 1876, was found in a layer of the Upper Brushy Basin Member of the Morrison Formation, dating from the Tithonian.

In Lily Park, Moffat County, James Leroy Kay and Albert C. Lloyd in 1955 recovered CM 21786, a skeleton lacking skull and neck.

This site, unintentionally exposed by a bulldozer, was found to contain fossil fragments, said to be in such condition they looked like unfossilized bone.

In the Late Jurassic Morrison formation of Western North America, Dryosaurus remains have been recovered from stratigraphic zones 2–6.

In 1877 this formation became the center of the Bone Wars, a fossil-collecting rivalry between early paleontologists Othniel Charles Marsh and Edward Drinker Cope.

The Morrison Basin where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan, and was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west.

[citation needed] The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs such as Brontosaurus, Camarasaurus, Barosaurus, Diplodocus, Apatosaurus and Brachiosaurus.

[22] Other animal taxa that shared this paleoenvironment included bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaur.

The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers.

[23] 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.