 Their decreasing size made them more vulnerable to heat loss because it increased their ratios of surface area to mass, and thus forced them to increase internal heat generation and thus become full endotherms.On the other hand, dinosaurs became medium to very large animals and thus were able to retain the "intermediate" type of metabolism.Armand de Ricqlès discovered Haversian canals in dinosaur bones, and argued that there was evidence of endothermy in dinosaurs.