"Mammals give birth to living younglings"
Mammals give birth to living offspring, except if they live in Australia and New Guinea. You can find there: Platypus (Ornithorhynchus anatinus) and Echidna (Short-beaked Echidna, Sir David's Long-beaked Echidna, Eastern Long-beaked Echidna and Western Long-beaked Echidna), two species that lay eggs first, and after that nurse the hatched offspring. They are called monotremes and they share anatomical characteristics of mammals and reptiles. In common with mammals, they have warm blood, body covered with hair, mammary glands, a single jaw bone and three middle-ear bones. In common with reptiles and marsupials they have no connective structure between the two brain hemispheres and a single cloaca.
dpeaici: Monotremes live long, have a low reproduction rate and they take care of their infants a relatively long period of time.
As with marsupials, mammals that lay eggs are a kind of intermediate station in the evolution of mammals.