The question of whether dinosaurs lacked effective temperature control (were heterotherms) or were endothermic homeotherms has given rise to much controversy. Their reptilian character suggests heterothermy; in contrast, their rise to dominance over early mammalian stocks suggests high physiological efficiency - homeothermy. Despite much argument, the criteria considered to date do not yield a convincing answer. Such an answer may be obtained from oxygen isotope ratios in dinosaur bone. A basic premise, well substantiated, is that the isotopic composition of bone reflects two variables: the composition of the body fluids from which it was deposited, and the temperature at which deposition occurred. A second premise, also well established, is that the isotopic ratios in the body fluids of an individual are uniform at any one time. This implies that any isotopic differences in bone deposited in a given individual at any time will reflect differences in temperature. Observations to date suggest that in mammals, body temperatures vary only slightly between extremities and body core, whereas notable differences exist in heterothermic reptiles (such as the Komodo dragon). Isotopic values will be compared from extremital and body core bones selected from articulated or partially articulated dinosaur skeletons. The results will give the first direct evidence of dinosaur thermal physiology.
