A Heart of Stone by Fred Bervoets
by Fred Bervoets
In 1993 amateur fossil hunter Michal Hammer discovered the fossil remains of the dinosaur Thescelosaurus in the Late Maastrichtian Hell Creek Formation. The specimen is called \"Willo\" in honor of the wife of a rancher who owns the discovery site in northwestern South Dakota near Buffalo.
During the studying and preparing of the specimen by Dr. Dale Russell paleontologist at North Carolina State University together with a team of North Carolina paleontologists the team came across a circular shaped, reddish-brown, grapefruit sized lump located in the chest cavity, now described in Science magazine as what may be the until now only known fossilized heart of a dinosaur.\"It\'s truly amazing that this animal seems to have had such a highly evolved heart,\" Russell told reporters.
The CT scan results, astounded the team when they found traces of the heart\'s internal structure which consisted a four chambered heart with a single aorta. This heart type is very similar to birds, but is vastly different from the three chambered hearts seen in modern day reptiles, adding substantially to evidence suggesting that at least some dinosaurs had high metabolic rates an idea proposed by Robert Bakker and John Ostrom in the late 1960\'s. The specimen is on public display in the N.C. Museum of Natural Sciences.
A four-chambered heart would mean that the blood circulatory system of dinosaurs was much more advanced than previously believed, that the animals were more tolerant of temperature extremes, and that they were capable of rapid and sustained movement typical of modern birds and mammals.
Russell states that possibly both lineages, and maybe all dinosaurs, had highly evolved hearts, and were capable of high metabolic activity. Possibly, he stated, this physiology may have evolved independently, or possibly it may stretch back to a common ancestor some 235 million years ago.
Russell explained that a single aorta implies the creature kept its oxygenated and deoxygenated blood separate in its heart -just like mammals and birds, which use their aortas to pump oxygenated blood to the body, while sending de-oxygenated blood to the lungs by another vessel, the pulmonary artery.
Sending only oxygen-rich blood to the body allows an animal to maintain a higher metabolism and body temperature and to be more active.
George Olshevsky noted \"Whe have to remember that the shape of this heart indicates a high activity level with these animals, but does not necessarily indicate whether animals were endo- or ectothermic. High activity level follows from perfect blood aeration (and separation of lowpressure pulmonary circulation from highpressure systemic circulation), but endothermy is not necessary for high activity level.\"
\"It\'s an efficient heart: The aorta is strong, so this must be a body that didn\'t mess around,\" said Russell. However, Chris Brochu, a paleontologist at Chicago\'s Field Museum said \"I am not convinced that this is a heart,\" \"Part of this stems from the extreme unlikelihood of a heart being preserved in isolation.\"
American Museum of Natural History paleontologist Mark Norell said \"It\'s exciting to see another set of data to bolster our case for a close relationship between dinosaurs and birds,\" but, he also noted. \"All of this will undergo critical review in the next couple of years. We will just have to wait and see how it shakes out.\" University of Chicago paleontologist Dr. Paul Sereno agrees.
In an interview with New York Times reporter John Noble Wilford Sereno said he \"questioned whether internal organs could have been preserved in the sediments where the specimen was found.\"
Sereno\'s statement is backed up with the fact that no other internal organ preservation has been discovered in the South Dakota sediments that bore this Thescelosaurus skeleton.
Organ preservation has only been noted once before, in the fossilized skeleton of a baby Scipionyx theropd discovered in near Rome, Italy earlier this decade, when Italian researchers used ultraviolet light to peer inside the chest of a fossil baby dinosaur and found its organs were laid out like a bird\'s or mammal\'s.
The \"ironstone\"-cemented fossils from the Hell Creek Fm. are almost always cemented by one or more of the following minerals: siderite (an iron carbonate mineral), \"limonite\" (a mix of goethite/hematite), goethite, and (rarely) hematite alone. In increasing order of difficulty to prepare, siderite and goethite tend to be the easiest to remove, and \"limonite\"- and hematitecemented matrix tends to be the worst to remove.
The news of a fossil dinosaur heart brings to mind this passage from Samuel W. Williston\'s 1914 classic book Water Reptiles of the Past and Present, in the chapter on crocodilia (pg. 199).
..[T]he crocodiles differ from all other living reptiles in having a four-chambered heart, like that of birds and mammals, that is, a heart with two auricles and two ventricles.
This more perfect structure of the circulatory organs does not, however, insure, at all times a complete separation of the pure or arterial blood from the impure or venous blood, since the blood may be more or less intermixed outside of the heart by a connection between the venous and arterial systems. Whether these imperfectly developed organs, so suggestive of a higher and more perfect mode of respiration, are the vestiges of what were once among some reptiles functional structures, or whether they are rudiments of a higher organization, developing independently in these creatures, cannot be positively determined, but it seems very probable that, far back in geological times.
Some reptiles, especially the pterodactyls and dinosaurs, had their respiratory and circulatory systems more like those of the birds and mammals of today. Unfortunately, however, if such was the case, we may never be able to prove it, although proof would not be impossible; stranger things than fossil hearts have been found by paleontologists!
Sources: George Olshevsky, Phillip Bigelow, Samuel W. Williston, Thomas, R. Holtz Jr., Steve Brusatte, Jeff Hecht