time Late Jurassic to Early
Cretaceous locality: North America (Colorado, Utah and Wyoming), Africa (Tanzania). Possibly Australia and Europe (England and Romania) size: up to 10 ft/3 m long Dryosaurus (also known as Dysalo-tosaurus) was one of the largest of the hypsilophodonts. Although it was also one of the earliest, its anatomy was advanced in several ways. For example, each long, slender leg had only 3 toes. And there were no teeth in the front part of the upper jaw; the horny beak at the front of the lower jaw met with a tough, toothless pad opposite on the upper jaw — an efficient arrangement for cropping vegetation.
Like other members of this family of long-legged sprinters, Dryosaurus' shin bones were much longer than its thigh bones. The heavy leg muscles were concentrated around the short thigh bones, and the lower leg and long feet were operated by light but powerful tendons. This arrangement gave Dryosaurus extra speed, and is exactly the same pattern possessed by modern deer and gazelle.
Dryosaurus was obviously a wide-ranging ornithopod, living as far apart as western North America and East Africa. In Jurassic times, these continents were only separated by a fledgling North Atlantic Ocean, and animals could still migrate across land by way of Europe and via the Siberia/Alaska link. This is why the dinosaurs found in the fossil-rich beds of the Morrison Formation in the western USA are so similar to those found in Tendaguru Hill of Tanzania.
Dryosaurus would, therefore, have shared its world with giant plant-
dryosaurus
dryosaurus eating dinosaurs such as Apatosaurus (= Brontosaurus), Diplodocus and Brachi-osaurus; small, rapacious carnivores like the coelurosaurs C oelurus and Elaphrosaurus; and large carnosaurs like Allosaurus and the horned Ceratosaurus.
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