 Larger bodied specimens of Dimetrodon have larger sails relative to their size , an example of positive allometry . Positive allometry may benefit thermoregulation because it means that , as individuals get larger , surface area increases faster than mass . Larger @-@ bodied animals generate a great deal of heat through metabolism , and the amount of heat that must be dissipated from the body surface is significantly greater than what must be dissipated by smaller @-@ bodied animals . Effective heat dissipation can be predicted across many different animals with a single relationship between mass and surface area . However , a 2010 study of allometry in Dimetrodon found a different relationship between its sail and body mass : the actual scaling exponent of the sail was much larger than the exponent expected in an animal adapted to heat dissipation . The researchers concluded that the sail of Dimetrodon grew at a much faster rate than was necessary for thermoregulation , and suggested that sexual selection was the primary reason for its evolution . 
