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Updated on December 11, 2009

Monotremes are egg-laying mammals of the sub-class Prototheria, the most primitive of living mammals. There are only two families, the duck-billed platypus of Australia and the spiny anteater (Echidna) of New Guinea and Australia.

Monotremes have certain features similar to reptiles, birds, marsupials and placental mammals and their classification was the center of controversy between anatomists in the 19th century.

Monotremes comprise the order Monotremata of the class Mammalia and are represented by the Platypus and the Spiny Anteater or Echidna. They are found only in Australia and New Guinea and no fossilized evidence of their existence has been found in any other part of the world.

Monotremes share a number of features with reptiles: both lay eggs with shells and large yolks; monotremes have the combined urino-genital and anal openings common in all reptiles; and the structure of some parts of a monotreme's skeleton, such as the shoulder girdle, is reptile-like.

However, apart from the fact that they lay eggs instead of giving birth to live young, monotremes possess all the features of mammals, being warm-blooded, furred vertebrates which breathe air and suckle their young. The young are protected in a temporary pouch (marsupium). Male platypuses are unique in that they posses a venom gland and a spine on the hind-foot; the use of these features is disputed.

Unfortunately, the only fossils of monotremes found so far resemble the living species. Because monotremes are very specialised animals, one living on land and feeding on insects, the other leading an aquatic existence and feeding on aquatic invertebrates, the fossils give no clues as to the relationships and ancestry of these animals. Furthermore, the adults do not have teeth which are an important guide to mammal relationships as they are often the only fossil remains.


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    • profile image


      7 years ago

      i love these animals they are so cute love the way tehy eat there food with there toungs

    • dusanotes profile image


      8 years ago from Windermere, FL

      I could use a hudgehog or, as you call them, Monotremes. No teeth? What do they do suck in the insects and digest them away? Interesting mammals, aren't they. Thanks for this most interesting lesson. Don White

    • lorlie6 profile image

      Laurel Rogers 

      8 years ago from Bishop, Ca

      A temporary pouch? Wow-this is fascinating-and like dohn, I thought the only egg-laying mammal was the platypus.

      Science has never been my forte, but I really appreciate this information!

    • darkside profile imageAUTHOR


      8 years ago from Australia

      We have echidna's here. And by here I don't mean because I'm in Australia, but living on the property. But I think they've moved into the bush since we moved in because we have dogs. I found two having a cuddle under the kitchen window in the garden.

      As for the platypus, I haven't yet seen one in the wild. They are very shy, as most wild animals are, but they do a good job of making themselves scarce. I think the creek down the back might be a good place for them to hang out, but I doubt I'd be patient enough to wait around long enough to get a chance to see one.

    • frogdropping profile image


      8 years ago

      Hmmmmm - I think they're similar to what we call hedgehogs over here. From a different family though. I don't think you get them in Australia. They're a great addition to the garden though - they eat a whole heap of insects.

      Odd how similar the two species look and yet they're not related. Nature is pretty inventive :)

    • dohn121 profile image


      8 years ago from Hudson Valley, New York

      Such great facts. Until today, I had no idea that there were such a thing and that monotremes exist. The duckbill platypus (I thought until now) were the only know mammals that laid eggs. Thanks darkside!


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