Complex sentence: Mammals (class Mammalia) are a clade of endothermic amniotes distinguished from the reptiles and the birds by the possession of hair, three middle ear bones, mammary glands in females, and a neocortex (a region of the brain).
Split into simpler sentences: Mammals (class Mammalia) are a clade of endothermic amniotes. Among the features that distinguish them from the other amniotes, the reptiles and the birds, are hair, three middle ear bones, mammary glands in females, and a neocortex (a region of the brain).