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Endotherms are animals such as modern birds and mammals that keep their body temperatures constant. For instance, humans are endotherms and maintain an internal temperature of 37℃, no matter whether the environment is warm or cold. Because dinosaurs were reptiles, and modern reptiles are not endotherms, it was long assumed that dinosaurs were not endotherms. However, dinosaurs differ in many ways from modern reptiles, and there is now considerable evidence that dinosaurs were, in fact, endotherms.
恒温动物是指诸如现代鸟类和哺乳动物这种可以保持体温恒定的动物。比如，人是恒温动物，无论环境温度是怎样，体温都维持在37℃。因为恐龙属于爬行动物，而现代的爬行动物都不属于恒温动物，所以长期以来恐龙都被当做是变温动物。然而，恐龙在很多地方都同现在的爬行动物不一致。同时，现在有大量的证据表明恐龙其实是恒温动物。
Polar dinosaurs
One reason for believing that dinosaurs were endotherms is that dinosaur fossils have been discovered in Polar Regions. Only animals that can maintain a temperature well above that of the surrounding environment could be active in such cold climates.
极地恐龙
主张恐龙属于恒温动物的原因是在极地发现了恐龙。只有能够很好维持体温的动物才能在如此寒冷的地方生存。
Leg position and movement
There is a connection between endothermy and the position and movement of the legs. The physiology of endothermy allows sustained physical activity, such as running. But running is efficient only if an animal's legs are positioned underneath its body, not at the body's side, as they are for crocodiles and many lizards. The legs of all modern endotherms are underneath the body, and so were the legs of dinosaurs. This strongly suggests that dinosaurs were endotherms.
腿的位置和运动方式
恒温动物和腿的位置及运动方式有一定联系。恒温动物的生理结构允许它们进行持续的物理运动，比如奔跑。但是，只有当腿长在身体的下部而不是两侧的时候才能快速地奔跑，而像鳄鱼或者很多蜥蜴的腿，都是长在身体两侧的。所有现代恒温动物的腿都是长在身体下部的，而恐龙的腿也具有同样的特点。这很有力地说明了恐龙是恒温动物。
Haversian canals
There is also a connection between endothermy and bone structure. The bones of endotherms usually include structures called Haversian canals. These canals house nerves and blood vessels that allow the living animal to grow quickly; and rapid body growth is in fact a characteristic of endothermy. The presence of Haversian canals in bone is a strong indicator that the animal is an endotherm, and fossilized bones of dinosaurs are usually dense with Haversian canals.
哈弗森管
恒温动物和骨结构之间也有相应的关联。很多恒温动物都有一种名为哈弗森管的骨结构。这种哈弗森管可以保护神经和血管以保障动物快速地生长，而快速生长恰恰是恒温动物的一个特征。哈弗森管的存在可以有力的说明该动物属于恒温动物，而恐龙的骨骼化石中常常可以观察到哈弗森管。
