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Biophysical Constraints on the Thermal Ecology of Dinosaurs

Michael P. O'Connor and Peter Dodson
Paleobiology
Vol. 25, No. 3 (Summer, 1999), pp. 341-368
Published by: Paleontological Society
Stable URL: http://www.jstor.org/stable/2666002
Page Count: 28
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Biophysical Constraints on the Thermal Ecology of Dinosaurs
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Abstract

A physical, model-based approach to body temperatures in dinosaurs allows us to predict what ranges of body temperatures and what thermoregulatory strategies were available to those dinosaurs. We argue that 1. The huge range of body sizes in the dinosaurs likely resulted in very different thermal problems and strategies for animals at either end of this size continuum. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in the absence of insulation. The smallest animals in which metabolic heating resulted in predicted body temperatures $\geq 2^\circ$C above operative temperatures (T$_e$) weigh 10 kg. Body temperature would respond rapidly enough to changes in T$_e$ to make behavioral thermoregulation possible. 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 adjusting metabolic rate and blood flow. Behavioral thermoregulation by changing microhabitat selection would likely have been of limited utility because body temperatures would have responded only slowly to changes in T$_e$. 4. Endothermic metabolic rates may have put large dinosaurs at risk for overheating unless they had adaptations to shed the heat as necessary. This would have been particularly true for dinosaurs with masses >10,000 kg, but simulations suggest that for animals as small as 1000 kg in the Tropics and in temperate latitudes during the summer, steady-state body temperatures would have exceeded 40$^\circ$C. Slow response of body temperatures to changes in T$_e$ suggests that use of day-night thermal differences would have buffered dinosaurs from diel warming but would not have lowered body temperatures 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 situations that demanded marked seasonal adjustment of metabolic rates and/or precise control of metabolism (and heat-loss mechanisms) as typically seen in endotherms.

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