DnaG
That’s the first answer that came up on google
1. Well developped offspring, and portable baby food despencing. Mamalian young are generally quite well developed when they are born, and the parent does not need to find any specific types of food for the new born since the mother already provides te perfect nutrition.
2. Internal heating allows mammals to remain quick and active in cold climates.
3. Fur is really effective and cheap to produce.
