Most of these studies give two thermoregulatory roles for the sail of "Dimetrodon": one as a means of warming quickly in the morning, and another as a way to cool down when body temperature becomes high. "Dimetrodon" and all other Early Permian land vertebrates are assumed to have been cold-blooded or poikilothermic, relying on the sun to maintain a high body temperature. Because of its large size, "Dimetrodon" had high thermal inertia, meaning that changes in body temperature occurred more slowly in it than in smaller-bodied animals. As temperatures rose in the mornings, the small-bodied prey of "Dimetrodon" could warm their bodies much faster than could something the size of "Dimetrodon". Many paleontologists including Haack have proposed that the sail of "Dimetrodon" may have allowed it to warm quickly in the morning in order to keep pace with its prey. The sail's large surface area also meant heat could dissipate quickly into the surroundings, useful if the animal needed to release excess heat produced by metabolism or absorbed from the sun. "Dimetrodon" may have angled its sail away from the sun to cool off or restricted blood flow to the sail to maintain heat at night.