Biophysical constraints on the thermal ecology of dinosaurs

A physical, model-based approach to body temperatures in dinosaurs allows u s to predict what ranges of body temperatures and what thermoregulatory str ategies were available to those dinosaurs. We argue that 1. The huge range of body sizes in the dinosaurs likely resulted in very di fferent thermal problems and strategies for animals at either end of this s ize continuum. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in t he absence of insulation. The smallest animals in which metabolic heating r esulted in predicted body temperatures greater than or equal to 2 degrees C above operative temperatures (T-e) weigh 10 kg. Body temperature would res pond rapidly enough to changes in T-e to make behavioral thermoregulation p ossible. 3. Body temperatures of large dinosaurs (>1000 kg) likely were sensitive to both metabolic rate and the delivery of heat to the body surface by blood flow. Our model suggests that they could adjust body temperature by adjusti ng metabolic rate and blood flow. Behavioral thermoregulation by changing m icrohabitat selection would likely have been of limited utility because bod y temperatures would have responded only slowly to changes in T-e. 4. Endothermic metabolic rates may have put large dinosaurs at risk for ove rheating unless they had adaptations to shed the heat as necessary. This wo uld have been particularly true for dinosaurs with masses >10,000 kg, but s imulations suggest that for animals as small as 1000 kg in the Tropics and in temperate latitudes during the summer, steady-state body temperatures wo uld have exceeded 40 degrees C. Slow response of body temperatures to chang es in T-e suggests that use of day-night thermal differences would have buf fered dinosaurs from diel warming but would not have lowered body temperatu res sufficiently for animals experiencing high mean daily T-e. 5. Endothermic metabolism and metabolic heating might have been useful for intermediate and large-sized (100-3000 kg) dinosaurs but often in situation s that demanded marked seasonal adjustment of metabolic rates and/or precis e control of metabolism land heat-loss mechanisms) as typically seen in end otherms.