Viewpoint: Yes, the most recent fossil evidence indicates that at least some dinosaurs were hot-blooded animals.

Viewpoint: No, the long-standing view of dinosaurs as cold-blooded animals is still the most compelling; recent evidence may suggest, however, that some dinosaurs had hybrid metabolisms, or aspects of both hot-and cold-bloodedness.

Naturalists have speculated about the nature of fossils since the time of Aristotle (384-322 B.C.), but it was not until the seventeenth century that these remarkable objects were generally recognized as the remains of ancient plants and animals. The work of the great French comparative anatomist and geologist Georges Cuvier (1769-1832) established the foundations of pale-ontology, the study of fossilized remains, and stimulated interest in the systematic study of fossils. Richard Owen's (1804-1892) investigations of reptilian fossils led to the discovery that some of these specimens were quite distinct from modern lizards. In...