Final answer:
Endothermy and high metabolic rate are characteristic features observed in mammals. Mammals regulate their body temperature internally by keeping their metabolic rate high, generating heat through extra mitochondria in their cells, and shivering to produce heat bursts.
Step-by-step explanation:
Endothermy and high metabolic rate are characteristic features observed in mammals. Endothermy refers to the regulation of body temperature internally through metabolic or physical changes. This allows mammals to maintain a stable body temperature and high activity level regardless of the outside temperature. Mammals achieve this by keeping their metabolic rate high, generating heat through the extra mitochondria in their cells, and shivering to produce bursts of heat.