Family Ornithorhynchidae
Platypuses
Family Tachyglossidae
Echidnas (Spiny Anteaters)
Platypus Long-nosed Echidna
Short-nosed Echidna
This is a small and unique order of mammals placed by themselves in the subclass Prototheria. There are only 3 living species of monotremes — one species of duck-billed platypus and two species of echidna. Very little is known about them from the fossil record. What makes these mammals so unique is their egg-laying ability, a trait found in no other mammals. This makes them more like birds than mammals in some respects, and indeed they do have highly modified snouts that resemble beaks, and the adults do lack teeth. They are also like reptiles in other respects — even though they are warm-blooded their body has a hard time adjusting to temperature and they can die of heat stroke. However, they produce milk for their offspring by way of mammary glands, they have hair and not feathers, they have 3 inner ear bones, and the lower jaw consists of a single bone. These are all characteristics of mammals.
Monotremes are only found in Australia and New Guinea. The platypus is typically found in aquatic environments and is an avid swimmer; echidnas and mainly terrestrial and are poor swimmers.
There were previously thought to be 6 species of monotremes: 1 platypus and 5 echidnas. However, the 5 species of echidnas are today grouped as 2 species. There are 2 families:
Ornithorhynchidae (platypuses) 1 spp
Tachyglossidae (echidnas) 2 spp
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