Concepts and Controversy

Endothermy / Exothermy Page 1
For many years the word reptile has had an unfair stigma attached to it. In many minds the reptiles represent the bottom most rung of vertebrates: slow, lethargic and endothermic. Pterosaurs are reptiles, and hence must have been endothermic... Or were they?

If modern flying organism are examined, one would find that both birds and bats are exothermic. Insects by strict definition are cold blooded; however in flight they become effectively exotherms. The energy generated by the shear physical exertion of flight causes the blood to warm to temperatures higher than that of ambient air.

Were Pterosaurs exotherms? The answer is probably yes. Unfortunately there isn't much direct evidence. The shear physical requirements of flight seem to force exothermy. Flight by necessity is an aerobic activity; energy must be supplied continuously. A high metabolic rate is required to produce this continuous supply of energy.

However most exotherms have some sort bodily covering to help insulate the body against unnecessarily heat loss (bats have fur, birds feathers and insects have a limited hoary covering (bumblebees)).



© Patrick Lyons 1998.