Although endothermy is in principle the most reliable way to maintain a fairly constant temperature, it is expensive; for example modern mammals need 10 to 13 times as much food as modern reptiles.
Iako je endotermija u principu najpouzdaniji način održavanja relativno konstantne temperature, skupa je; današnji sisavci, na primjer, trebaju 10 do 13 puta više hrane od današnjih gmazova.