Abstract
Comparative anatomists since the time of Richard Owen (1) have observed that birds and crocodilians have a four-chambered heart and have speculated that such a heart was present in extinct archosaurs as well. Until recently, no direct evidence of the cardiovascular system had been reported in any archosaur fossil. Fisher et al. (2), however, using computerized tomography (CT) scanning, reported the discovery of a four-chambered heart with a single systemic aorta within the chest region of a dinosaur fossil dating from the Cretaceous. Even more surprising, the specimen reportedly was collected from channel sandstones of the Hell Creek Formation, a fluvial setting that rarely preserves soft tissues. Examination by one of us (Rowe) of the specimen in the North Carolina State Museum of Natural Science and examination of the CT imagery (3), however, lead us to conclude that the object is not a fossilized heart but an ironstone concretion. Such concretions are commonly found in Upper Cretaceous fluvial sediments of the North American western interior, often in association with dinosaur bones.
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