What we found

Our findings contradicted the claim that larger body size conferred greater and greater circulatory control over reptiles' thermal energy balance.

We found that circulatory control of heat exchange peaked at a body mass of roughly 5 kg body mass. At body masses smaller than 5 kg, the ability to control heat exchange with circulation lessened. The same was true for body masses greater than 5 kg, and had only slight effect at the largest body size of our sample, roughly 50 kg.

When we compared our results against those that had claimed greater physiological control at large body size, we found that our data matched closely. The claim of greater control at large body size was a statistical artifact.

We also found a significant effect of body shape. At small body sizes, conduction heat exchange at the torso was so large that ay effect of circulation would be negligible. At large body size, boundary layer effects were so large that circulation within the torso would have little influence on total flows of heat. At larger and larger body sizes, what control did exist was due to increasing reliance of heat exchange in appendages (legs and tail) to manipulate heat exchange.

Further reading

Turner, J. S. (1987). The cardiovascular control of heat exchange: Consequences of body size. American Zoologist. 27: 69-79.

Turner, J. S., K. A. Hammond, et al. (1980). Energy flux at the appendages and trunk of the American alligator during heating and cooling. Anatomical Record 196: 192A.

Turner, J. S. and C. R. Tracy (1983). Blood flow to appendages and the control of heat exchange in American alligators. Physiological Zoology 56: 195-200.

Turner, J. S. and C. R. Tracy (1985). Body size and the control of heat exchange in alligators. Journal of Thermal Biology 10: 9-12.

Blood flow pages

Heat exchange

Why alligators?

What we did

What we found