 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 . 
