Yes, some soft parts impressions of dinosaurs have been found in the past, but they are rare. Plus, some fossils display the outlines of internal organs; and some animals have fossilized remains inside them of what the dinosaur had just eaten. One of the most exciting discoveries is housed in the North Carolina Museum of Natural Science: the first-ever discovery of traces of a dinosaur heart in a fossil nicknamed “Willo.” This dinosaur was a member of the group known as Tescelosaurus (“marvelous lizard,” living about 66 million years ago), a 600 pound, hog-like plant eater about the size of a pony. Its long, bony tail gave it a total length of about 13 feet (4 meters).

Using special equipment to see “inside” the dinosaur’s body, researchers developed a three-dimensional view of the heart. The organ had four highly developed chambers and a single arched aorta. This one discovery—found in North Dakota—changed the way many scientists look at dinosaurs. In particular, it provided evidence that some of the long-extinct beasts were quick and possibly warm-blooded like birds (a complex heart is usually indicative of a high metabolism), not slow and plodding like some contemporary reptiles.