Cold-hearted Reptiles

It was a deduction to make Sherlock Holmes queasy with envy. From the subtle curve of just a few ribs, Richard Owen declared that the dinosaurs had an advanced circulatory system to cope with what he believed was a rising level of oxygen in the atmosphere during the Cretaceous Period. With this grand conjecture, Owen aimed to refute the Lamarkian theory of evolution and its notion of increasing biological complexity.

Audacious though it was, Owen was not merely following his preconceptions; he was Britain's chief practitioner of the method of comparative anatomy invented by French naturalist Georges Cuvier. This technique could reconstruct an entire animal from a single bone based on similarities with known animals. Though not infallible, Cuvier and Owen were right often enough to gain enormous respect, such as when Owen predicted the size and character of the extinct moa of New Zealand from a chunk of leg bone.

Ideas about dinosaurian metabolism were colored from the outset by lumping them with reptiles. Reptiles were synonymous with cold-bloodedness--the need to absorb external heat to power bodily functions. Since Owen's antievolutionary argument relied on dinosaurs being better than modern reptiles, but still closely related, he always assumed that dinosaurs were cold-blooded.

History might have been different if the first dinosaurs to be described had been the smaller, obviously birdlike species. If they had been compared to birds instead of reptiles from the start, the warm-bloodedness of the group as a whole would have been assumed. As it was, the hot/cold-blood debate gave paleontologists something to argue about for 150 years.