How are platypuses mammals if they lay eggs?

Answer 1

They're mammals because they have all the characteristics used to define mammals, and the mode of reproduction is not one of them.
The exclusive characteristics of any group of living beings are called diagnostic characters.

In the case of mammals, the main diagnostic characters are:

1) Possession of hair (fur, wool, and all its variations).

2) Possession of mammary glands that produce milk which is fed to the young (note that having nipples is not the same; in fact platypuses lack these, but still feed their young with milk).

3) The lower jaw is formed by a single bone, the dentary (indeed, if you find a lower jaw without its teeth or skull, you can tell if it belongs to a mammal by this single character).

4) The middle ear has 3 ossicles (small bones called hammer, anvil and stirrup, or more technically malleus, incus and stapes).

In mammals, reproductive mode (egg-laying, live-bearing + development in a pouch or full live-bearing) is one of the characters used to classify species into the three major groups. Thus, live-bearing does not define whether an animal is a mammal, but it does define which type of mammal it is. Egg-laying mammals are Monotremes like the platypus and echidnas; pouched mammals are Marsupials or Metatheria, like opossums and kangaroos; and placental mammals are Eutherians, like e.g. humans, dogs, bats or whales.

Also, homeothermy (warm-bloodedness) is NOT a defining characteristic of mammals. Birds are warm-blooded, as well as some turtles, sharks and bony fish. And some mammals are only imperfect homeotherms.

See more about mammals in the Animal Diversity Website:
http://animaldiversity.ummz.umich.edu/site/accounts/information/Mammalia.html

Answer 2

Platypuses are the odd ball of all animals, They have fur like mammals, have a bill like a duck, a tail like a beaver, are marsupials like a kangaroo, are endothermic unlike reptiles, and lay eggs.

The key criteria of a mammal is that all mammals nurse their babies. In many languages the word used for mammal actually means one that nurses. Anyway, platypus are marsupials, they have a pouch were their young lives in and is feed by the mother's utter (just like a kangaroo). All marsupials are mammals so platypus are mammals.

Answer 3

The duckbilled platypus and spiny anteater are regarded as one of the most ancient mammals, monotremes, since it has characteristics of both reptiles and mammals...though it does not have a placenta, like most modern mammals, it lays eggs,and when hatched are nursed by the mother, at a very immature state, and they suck milk that secretes through the glands of the mother.

Answer 4

Mammal=mammary. Some other organisms have live birth. We are placental mammals and platypuses are monotremes.

Answer 5

1) They have fur, not feathers or scales
2) They are endotherms ("warm blooded")
3) They nurse their young.
With the exception of live birth, they fit all characteristics of a mammal. They are also not the only egg laying mammal. Echidnas are the same way.

Answer 6

They produce milk to feed their young. Milk comes from their mammary glands. That is why they are mammals. It is rare for a mammal to lay eggs, but the criterion is the production of milk for the babies.

Answer 7

They have all characteristics of mammals except laying eggs.But the fertilization of the egg is internal.Only hatching is external.

Answer 8

They are not mammals. They are marsupials which also nurse their young.

Answer 9

They nurse their young.