H.Huxley reasoned that flying vertebrates must have been warm-blooded because flying implies a high rate of metabolism, which in turn implies a high internal temperature.

• 赫胥黎对此解释说，飞翔脊椎动物肯定已经是热血动物，因为飞翔要求一个高新陈代谢率，后者要求一个较高的体温。