Monotremes are mammals that reproduce by laying eggs. The only living monotreme species are the platypus and echidnas. Platypus females lay their eggs in a burrow. Echidna females have a pouch in which they store their eggs.

How did monotremes evolve?

According to this suggestion the monotremes evolved from birds by losing the derived features that in birds were beneficial for flight. They are usually believed to have descended from the first radiation of mammals, which could explain their similarity to reptiles and birds.

Do monotremes give birth to young?

There is a group of mammals, called monotremes, that lays eggs instead of giving birth to live young. Monotremes are a pretty exclusive bunch. There is just one species of platypus that's alive today. There are three or four types of echidna, with several subspecies.