Answer:
Mammals have stronger more stable jaws because of the single bone structure.
Relatively larger brains require a high metabolic rate.
Internal heating allows mammals to remain quick and active in cold climates.
No eggs. Mammals have well-developed offspring that they can keep it safe inside their body until the time it is ready to be in the outside world.
Four legs under the body. It allows mammals to be highly developed when it comes to speed.
Fur. It protects the mammals’ skin.
(Pick whichever ones you like best!)
