Dryosaurus

Dryosaurus was a lightly built, fleet-footed herbivorous dinosaur that roamed North America during the Late Jurassic period, roughly 155 to 145 million years ago. Measuring around three to four metres in length, it was comparable in size to a large modern deer or small horse. Fossils from the Morrison Formation reveal a creature built entirely for speed, with slender hind legs, a stiff balancing tail, and short, five-fingered forelimbs. Its horny beak and cheek teeth were well suited for snipping and grinding ferns, horsetails, and other low-growing vegetation. Unlike some of its contemporaries, it completely lacked armour or defensive horns, relying entirely on keen eyesight and agility to outrun theropod predators.

It relied entirely on swift running on elongated hindlimbs to escape large Late Jurassic predators like Allosaurus.

Where and when

Dryosaurus lived in the Late Jurassic, from 155 to 145 million years ago (Kimmeridgian-Tithonian age). Its remains come from United States, in the Morrison Formation.

The numbers

Length 3.3 m (estimates run from 2.5 to 4 m). Mass about 77 kg. Hip height about 1.2 m. That is 1.9 human-lengths, or 0.29 of a double-decker bus. These are estimates from near-complete skeleton; fields marked estimated by the site are length, mass, hip height.

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