Monotremes are a unique group of egg-laying mammals, primarily found in Australia and New Guinea. The most well-known monotremes are the platypus and the echidna. Unlike most mammals, which give birth to live young, monotremes reproduce by laying eggs, which they incubate until hatching. These animals possess a mix of mammalian and reptilian traits. For instance, monotremes have fur and produce milk for their young, but they also have a cloaca, a single opening for excretion and reproduction, similar to reptiles. This combination of features makes monotremes an interesting subject of study in evolutionary biology.