A Thescelosaurus' fossilized four-chambered heart was recently found near Buffalo, South Dakota, USA. A CAT scan revealed a powerful, advanced heart that seems to indicate that Thescelosaurus was an active, warm-blooded animal.

The name Thescelosaurus means "Marvelous Lizard"; it was named by the paleontologist Charles W. Gilmore in 1913. The type species is T. neglectus.

Anatomy: Thescelosaurus had a small head, a bulky body, a long, pointed tail, and short arms. It was a hypsilophodontid and an ornithischian dinosaur about 10 to 13 feet (3-4 m) long and 3 feet (0.9 m) tall at the hips; it weighed roughly 665 pounds (300 kg). This ornithopod (a Hypsilophodontid) had a small skull, cheek pouches, cheek teeth, and a beak made of horn.

Fossils: One complete specimen and 8 incomplete Thescelosaurus skeletons, including skin impressions, have been found in Wyoming, Montana, and South Dakota in the USA and in Alberta and Saskatchewan, Canada.