משתמש:דליק הכלבלב/ארגז חול/יונקים

What is a mammal? You are faced with an unknown animal - how can you tell if it's a mammal or not?

If this is a living animal there are a few characteristics you can look out for:

Is it a warm-blooded animal? If you touch its skin is it warmer than its surroundings? If so, it could be a mammal, but this isn't a defining characteristic, though, because some mammals allow their body temperature to drop, and some animals which aren't mammals (such as birds) are also warm-blooded. Does it have hair? Even just whiskers? If so then it almost certainly is a mammal, but if not then it could still be a mammal, just one which has lost its hair. Be careful not to be fooled by some flightless birds, though, whose feathers may look like hair. Does it have mammary glands? These might be difficult to recognise, especially if your animal is a male, but most mammals also have teats (even males), which should give you a clue. In fact, mammary glands are the only feature that all mammals have and no other living animals do. If you've got a fossil animal, or just a skeleton then looking for hair, warm blood or mammary glands isn't going to help you. There are some other things you could do though.

Does it have teeth of different shapes? If so then you could be looking at a mammal.

Does it have a bar of bone on the skull which a part of the lower jaw fits under to form a joint? Are there little bones inside the inner ear? If so then you have a mammal.

In fact it is usually the structure of the jaw that is used as the definition of what is a mammal, but for living animals it is whether or not they have mammary glands that is the feature to look for. The mammary glands produce milk, the food that all mammals start life on, and this has had a real impact on the success of mammals, as we explore in the later sections of this website.