This particular specimen of Thescelosaurus (a little known species), was discovered in South Dakota in 1992 by professional fossil hunter and preparator Michael Hammer. The specimen was later purchased from the land owner by funds donated from the Friends of the Museum. Mr. Hammer was performing the preparation of the specimen when he saw a large, rusty stained concretion in the thoracic (chest) region of the dinosaur.
Mr. Hammer drew the attention of Dr. Russell to the rusty stained concretion, commenting that it was in the same area that the dinosaur's heart would have been, and could it possibly be a preserved heart? Initially, Dr. Russell felt that the concretion could not possibly be a preserved heart, but his curiosity was aroused. Could there be evidence of the heart structure in a dinosaur that died 66 million years ago, at the very end of the Cretaceous Period (140 to 65 million years ago)?
Dr. Russell took the Thescelosaurus to the Biological Imaging Facility at the College of Veterinary Medicine in the North Carolina State University, where Paul Fisher performed a CT scan of the specimen. They found "a tubular structure that resembled and was in the right position of an aorta," said Dr. Russell, still hesitant to call the concretion an actual heart. They also found two structures that resembled ventricles, thereby arousing their curiosity even more.
Further CT scans revealed the outlines of the "heart". Very interestingly, it did not resemble the structures of hearts seen in modern reptiles. Modern reptiles have a heart with a single ventricle and two aortae (the plural of aorta). This differs from the hearts of mammals, who have four chambered hearts with two ventricles and a single aorta. The CT scans showed a heart that resembled that of a mammal rather than a reptile.
The single ventricle and two aortae seen in modern reptiles allows oxygenated and de-oxygenated blood to mix together in the heart, and then be pumped to the body. The more sophisticated two-venticled heart of mammals keeps oxygenated and de-oxygenated blood separate, and is a factor in the higher metabolism seen in mammals versus reptiles.
