TOEFL Integrated Writing Practice Test 062Endotherms

Endotherms, such as modern birds and mammals, maintain a constant body temperature regardless of environmental conditions. For example, humans, as endotherms, keep their internal temperature at around 37℃, whether the surrounding environment is warm or cold. Traditionally, because dinosaurs were reptiles and modern reptiles are not endotherms, it was assumed that dinosaurs were also not endotherms. However, given that dinosaurs differ from modern reptiles in several ways, current evidence suggests that they were likely endotherms.

One reason for this belief is the discovery of dinosaur fossils in Polar Regions. Animals capable of surviving and being active in such cold climates must maintain a body temperature significantly higher than the surrounding environment.

Another indicator of endothermy is related to the positioning and movement of the legs. Endothermy supports sustained physical activity, such as running, which is most efficient when an animal’s legs are positioned directly underneath its body rather than at its sides, as seen in crocodiles and many lizards. The fact that dinosaurs had their legs positioned underneath their bodies, similar to modern endotherms, supports the idea that they were endotherms.

Bone structure also provides evidence for endothermy. Endotherms’ bones typically feature Haversian canals, which house nerves and blood vessels that facilitate rapid growth—a characteristic of endothermy. Fossilized dinosaur bones are often dense with Haversian canals, suggesting that dinosaurs were endotherms.