The sauropod dinosaurs, those long-necked, long-tailed giants, burst onto the world scene in the Lower Jurassic period and lived on until the end of the Age of Reptiles at the close of the Cretaceous. From the shapes of their teeth it is clear that they were herbivorous, and what an enormous amount of plant material they must have continuously consumed to fuel their gigantic bulk. Colbert (1962) estimated the weight of an adult Apatosaurus (Brontosaurus) at 34 metric tons, and that of Brachiosaurus at 78 metric tons. Dale Russell (see Russell, Beland and McIntosh, 1980) regards these estimates as too high by perhaps a factor of two, but in any case their masses were immense. The sauropods were quadrupedal, and their limbs were oriented in a columnar position as in large mammals, and unlike those of other dinosaurs. From this fact and a bone histology more nearly like that of mammals than typical reptiles, Bakker (1975) and de Ricqlès (1968, 1980) have independently suggested that the sauropods may have been warm-blooded (endothermic). Many dinosaur experts concede that this may have been true of some of the smaller, faster-moving carnivores, but the majority seem unconvinced of endothermy in the sauropods. Instead, it seems more appropriate to regard them as inertial homeotherms: that is, their large mass ensured a fairly constant body temperature, as in large mammals. However, as in mammals, the story is probably more complex than a single fact or factor can explain (Thomas and Olson, 1980; Weaver, 1983).