Gigantothermy

Gigantothermy is a phenomenon where large, cold-blooded (ectothermic) animals can maintain a stable, warm body temperature due to their relatively small surface area to volume ratio. Unlike mammals and birds, which are endothermic and generate their own body heat, ectotherms rely on external sources like the sun. However, for a very large ectotherm, the heat absorbed from the environment is lost much more slowly than it would be for a smaller animal. This is because the surface area through which heat can escape increases with the square of the linear dimension, while the volume (and thus the capacity to store heat) increases with the cube. Consequently, a large ectotherm can absorb enough heat during active periods to maintain a relatively constant and warm body temperature for extended periods, even during cooler conditions or at night.

This concept is often invoked to explain how large dinosaurs, which are presumed to have been ectothermic or perhaps mesothermic (partially endothermic), could have been active in various climates. Their massive size would have provided a significant thermal inertia, allowing them to maintain stable body temperatures. Without gigantothermy, it would be challenging for large ectotherms to survive and thrive, especially in environments with fluctuating temperatures. The principle highlights how body size can play a crucial role in thermoregulation for ectothermic organisms, enabling them to occupy ecological niches that might otherwise be inaccessible.