Monotremes are a subgroup of mammals that are known for their ability to lay eggs rather than giving birth to young ones which are a characteristic feature of all the groups of mammals and hence, monotremes are famously known as egg-laying mammals.
They are more commonly formed in Australia and New Guinea and some regions of South America.
Today, there are only 4 species of echidna and platypus that constitutes the existing monotremes.
