Mammals

Mammals descended from a group of reptiles that flourished before the time of the dinosaurs. The first true, furry mammals lived alongside dinosaurs, but during this time remained small shrew-like. They diversified only after the dinosaurs went extinct. Like birds, mammals became warm-blooded, and regulation of contant body temperature helped them stay active even in the cold But unlike birds, most mammals abandoned egg laying to give birth to live young, nourished by milk produced from their eponymous mammary glands.