Dryosaurus

Dryosaurus is a genus of herbivorous ornithopod dinosaur that lived during the Late Cretaceous period, approximately 75 million years ago. It is known from a single species, Dryosaurus altus, which was discovered in the Hell Creek Formation of North Dakota, USA. The genus name, Dryosaurus, means "tree lizard," while the specific name, altus, means "tall."

Dryosaurus is one of the largest known ornithopods, with an estimated length of around 10 meters (33 feet) and a weight of up to 5 metric tons (5.5 short tons). It had a long, slender snout filled with sharp teeth, which it likely used to graze on low-growing vegetation. Its legs were relatively long and slender, adapted for a fast gait, and it likely moved in a bipedal manner.

The skeleton of Dryosaurus is known from a partial specimen, including parts of the skull, vertebrae, ribs, and limb bones. Its most distinctive feature is the presence of a large, bony crest on the skull, which may have been used for display or communication. The crest is unique among ornithopods and is thought to have been a sexual dimorphism, with males having larger crests than females.

Dryosaurus is an important dinosaur for understanding the evolution of ornithopods and the diversity of Late Cretaceous ecosystems. Its large size and unique features make it a fascinating subject for paleontologists and dinosaur enthusiasts alike.