Tall Animals Are Endothermic: Height, Blood Pressure, and an Animal’s Thermal Regulation Mechanism

The pressure of a fluid varies with height, as discussed in every introductory physics course. This observation enables students to develop a methodology which shows that endothermic animals with their high metabolism can be taller than ectothermic animals with their low metabolism. The heart of an animal must generate sufficient pressure to pump its blood up to the highest part of its body. Tall animals must have a high blood pressure which requires the heart to beat at a faster rate, necessitating a high metabolism.1 Consequently, endotherms can be taller than ectotherms. The upper limit for the height above the heart to which blood can be delivered by ectothermic animals is determined as a function of body mass for extant species. All animals exceeding that height are identified as endothermic. This methodology can be applied to any animal for which the height above the heart and body mass have been determined, including extinct animals such as non-avian dinosaurs (hereafter called dinosaurs).