One of the great arguments in paleontology has flared up again with the discovery of a fossilized dinosaur heart by scientists from the North Carolina State Museum of Natural Sciences and North Carolina State University. Soft tissue, such as the heart muscle, is hardly ever found in fossilized form, and analysis of the structure of the fossilized heart-is adding more weight, to the idea that some dinosaurs may well have been warm-blooded.
The heart was found inside the skeleton of the scelosaurets, a small, plant-eating dinosaur dating back about 66 million years to the end of the dinosaur era. The anatomy of the heart was analyzed through a scanning technique called computerized tomography (CT) adopted from the healthcare industry. According to Paul Fisher, the lead author of a report on the findings, these scans “basically sliced the heart up like a loaf of bread.” The two-dimensional slices were then converted by a sophisticated software program into three-dimensional images which could be manipulated and studied on a computer screen. The initial images were shown to seven cardiologists. These experts all agreed that they were looking at two separate ventricles of a four-chamber heart connected to a large blood vessel, the systemic aorta.
The significance of the twin-ventricle, four-chamber heart is that it separates oxygen-rich and oxygen-lean blood in the circulators systems of up until now, only mammals. Most reptiles have single-ventricle, three-chamber hearts, but even in those with four chambers such as the crocodile, blood is pumped through paired arteries that mix blood, says team member Dale Russell.
The prevailing view on dinosaurs has been that they were cold-blooded animals, or more accurately ectotherms, and thus reliant on an external source of heat, usually the sun, for maintaining body temperature. However, some paleontologists maintain that it is possible that dinosaurs were endotherms, animals which generate heat through bodily processes and maintain heat regardless of most external conditions. There is circumstantial evidence for both arguments, but the weight of opinion has been on the ectothermic side. Deeper analysis of the first fossilized dinosaur heart may swing things the other way.
Not all scientists are convinced by the analysis of the scanned heart. The scan does not show major blood vessels.. The routing of these important structures decides whether the flow of oxygen-rich and oxygen-lean blood is independent or intertwined. Their failure to appear during the analysis may be because these Structures collapse at death and were therefore not fossilized, or because they were simply not revealed on the initial scan.
However, John Ruben, physiologist at Oregon State University in Corvallis, says the evidence at the moment is simply not sufficient to make any claims “There's no apparent trace of other major vessels that we know would have been there in life,” he says. “I think it's premature for them to say this is a heart of an endotherm,” Further scans may resolve the issue, but in the meantime the debate surrounding this prehistoric mystery continues.