Last April, scientists unveiled what they identified as a fossilized dinosaur heart. To the team, the birdlike heart was evidence that dinosaurs were warm-blooded (ScienceNOW, 20 April 2000). But in the 2 February Science Online, two paleontologists and a geologist argue that the grapefruit-sized structure is no heart at all but only a deceptive lump of minerals.
Fossilized organs are extraordinarily rare, even in the best conditions for preservation. So it was "a real stretch" to paleontologist Tim Rowe of the University of Texas, Austin, that a heart could have been fossilized in the delta rivers that coursed through South Dakota some 66 million years ago. Hungry bacteria in the flowing waters would have made short work of such tasty tissue, Rowe says.
Rowe says his skepticism is borne out by CT images that the fossil's investigators posted on the Web. One of the two supposed ventricles appears almost entirely closed and thus lacks any way for substantial amounts of blood to enter or leave, Rowe and his colleagues point out. Features of a normal heart, such as atria and coronary arteries, are missing. Rowe thinks the structure is an ironstone concretion. Such rocklike mineral deposits, precipitated by bacteria, are common in the Hell Creek Formation where the 4-meter-long Thescelosaurus was found, he says.
Dale Russell, a paleontologist at North Carolina State University in Raleigh, and co-author of the original Science paper, thinks the heart is getting a bad rap. The decay of heart tissue, he says, could have been delayed if the dinosaur lay in an anoxic, swamplike spot. The lack of detail is easily explained, Russell says: "This heart was rotten; it wasn't the kind of heart you can lay on a dissecting table." Russell and his colleagues have since scanned the putative heart at higher resolution and are searching for diagnostic details.
But even if the lump is a heart, says paleontologist Larry Witmer of Ohio University's College of Osteopathic Medicine in Athens, "it's not clear that it's telling anything about the biology of the animal," he says, because key features of the organ may have rotted away. The main scientific value of a certified heart, he says, would be as proof that the Hell Creek rocks hold more than just the bones of ancient creatures, thus encouraging paleontologists to look for better-preserved organs.