What features suggest that the platypus is a mammal?

Answer 1

Numerous features suggest that a platypus is not a fish.

• A platypus has fur; no fish has fur.
• A platypus uses a fully developed mammalian respiratory system to breathe, i.e. nose and lungs; fish receive oxygen via their gills.
• A platypus can move around on land, out of water, and its young are incubated and hatched on dry land; fish must reproduce in water.
• Platypuses are warm-blooded; fish are cold-blooded.

Answer 2

Other than the platypus's bill, which some may construe as bird-like in shape, all the features of a platypus suggest that it is not a bird. Even this bill serves a completely different function to that of any duck - the bill is fitted with electro-receptors, which is a feature no bird has. The platypus has a mammalian type of hip structure, it has fur rather than feathers, and it secretes milk to feed its young (although not in exactly the same way that most mammals do).

The only feature of the platypus that is remotely birdlike is the fact that it lays eggs. Even these are different to those of a bird. A bird's eggs are hard-shelled, while the platypus lays soft-shelled, leathery eggs.

Answer 3

They have fur, breathe through lungs, are warm-blooded, and they feed their young milk, though not through nipples, but through patches of skin that milk oozes out of.