My posts about echidnas seems to have generated both interest and confusion - so I will try to sort this out!
Mammals are a very familiar group of animals - many of our domesticated animals are mammals. All mammals have fur (or hair), produce milk and are 'warm blooded'. However, mammals are split into 3 groups based (more or less) on the way they reproduce.
The largest of these three groups are the placental mammals - these mammals are probably the most familiar of the mammals, and in most parts of the world they are basically the only mammals to be seen. The young of this type of mammal undergo a reasonable period of development inside the female and are nourished through a placenta. This type of mammal includes cows, cats, dogs, bats, seals, deer, whales and us. It also includes hedgehogs and porcupines. I'm a bit short of pictures of this sort of mammals, as I live in the only part of the world where they are not the dominant type of mammals. So - here are a few placental mammals.
|Humans (red-headed form!)
You can see that although all these mammals have fur or hair - the degree of furriness varies a lot between species! (And not all mammals have red hair either!).
The next group of mammals are marsupials - with very few exceptions marsupials occur in the Australian region. Opossums in America are a well known exception. These mammals give birth to tiny, underdeveloped young that continue to grow in a pouch after they have been born. Here are some marsupials.
Marsupials are a very diverse group - there are carnivores, omnivores and herbivores. In the not too distant past there were marsupials the size of small cars and ones that were similar in behaviour to lions and wolves - living in Australia today is probably a lot less risky then when these mega marsupials were alive.
The final group are the monotremes. These are egg laying mammals. Once the egg hatches the young animal continues its development in a pouch. The platypus is probably the best know monotremes, but there are also two species of echidna - only one of which, the short beaked echidna, lives in Australia. The other species of echidna is found in Papua New Guinea.
|Short beaked Echidna
So, thats a quick tour through mammals - and the final point I'd like to leave you with is this - we, as humans, are more closely related to hedgehogs and porcupines that echidnas! The fact that echidnas, hedgehogs and porcupines all have spines does not mean that they are closely related - although they probably all have them for similar reasons.
Hope you did not mind a quick burst of biology - once a teacher, always a teacher - just to show how unusual the echidna really is!