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This 66 million year old heart has recently been analyzed -- it has four chambers and a single aorta, which is quite different from existing reptiles, but is similar to modern warm-blooded animals (like birds and mammals).

If true, this discovery suggests not only that Thescelosaurus may have been warm-blooded, but that many other dinosaurs may have been warm-blooded as well. This is because we now have evidence of warm-bloodedness in both Ornithischia and Saurischia (the two major groups of dinosaurs, which diverged early in the Mesozoic Era). Thescelosaurus was an ornithischian; birds, which are known to be warm-blooded, are saurischians.

Finding fossilized soft tissue (like a heart) is extremely unusual. Soft tisssue usually decays long before it can fossilize (fossilization is a process in which rock-like minerals replace organic tissue, forming a rocky copy of the original material).

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.

RELATED LINKS
Rebuttal to the find from 2001: Tim Rowe, Earl McBride and Paul Sereno think that the "heart" is an ironstone concretion.

Printout on Thescelosaurus

North Carolina Museum of Natural Sciences, Raleigh, NC - where you can see Willo, the Thescalosaurus whose fossilized, four-chambered heart was found.

DinoHeart.org, a site on Willo

Information on dinosaur metabolism