Dryosaurus

Chapter • Meet the dinosaur

Overview

Dryosaurus altus was a slender, two-legged plant-eater roughly 2.4–4.3 metres long and weighing perhaps 70–100 kilograms – about the mass of a large deer, but built like a sprinter. It carried its body horizontally over the hips, balanced by a long, stiffened tail; there is no evidence that it dragged that tail along the ground. The skull was short and deep with unusually large eye sockets, and the front of the snout was toothless, covered instead by a horny beak. Behind the beak sat rows of leaf-shaped cheek teeth that ground against one another as the jaws closed. The hind limbs were long, and the lower leg was longer than the thigh – a hallmark of fast-running animals. The hands bore five fingers, while the foot rested on three strong toes. No skin impressions are known for Dryosaurus, so feathers or bristles cannot be demonstrated; most reconstructions show a scaly animal, possibly with simple filamentous structures like those found in some other ornithischians.

Chapter • Where it lived

Habitat

Dryosaurus lived in the Late Jurassic, roughly 155–148 million years ago, on the broad river plains of what is now the western United States. All secure finds come from the Morrison Formation in states such as Colorado, Utah and Wyoming, including the famous quarries at Dinosaur National Monument and Como Bluff. The setting was a seasonally dry lowland crossed by meandering rivers, with gallery forests of conifers and ginkgoes, fern prairies and wide open ground – a landscape where an alert, fleet-footed animal the size of a deer stood a reasonable chance of outrunning predators.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy