Why do platypuses lay eggs when they are mammals?

Answer 1

Platypus are a member of a very specialised, very exclusive group of animals called Monotremes (egg laying mammals). Along with the Short and Long Beaked Echidna, they are the only members of this group. Platypus are also one of the very few venomous mammals as well. Why do they lay eggs? Good question. I would assume that it is an adaptation that assists them in surival. It must work for them since they have been around since the time of dinasaurs. They are a true enigma.

http://en.wikipedia.org/wiki/Platypus
http://www.rainforest-australia.com/Platypus%20page%202.htm

Answer 2

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RE:
Why do platypuses lay eggs when they are mammals?

Answer 3

They are a special exception to the mammal species. They are monotremes meaning that they are egg-laying mammals. They're considered mammals because they have hair (fur) and produce milk. Another monotreme is an echidna.

Answer 4

Never thought about it. I wondered if it was because they were aquatic, but so are other mammals, like water rats, and the Echidna lays eggs, and it is land based.
Perhaps the ancestors of the monotremes were required to lay eggs to protect them the environment, such as drying out. Marsupials adapted pouches, monotremes used eggs.

I'm going to keep a watch on this and see what people say.

Answer 5

There are three different types of mammals.

Placental mammals who reproduce like people.

Marsupials like kangaroos who have brief pregnancies that result in tiny newborns that finish their development outside the mothers body cavity in a pouch.

And monotremes, egg laying mammals. Monotremes have several relictual (primitive) characteristics including laying leathery reptile-like eggs and the lack of distinct nipples. The milk kind of sweats out in patches on the mothers underside. The other relictual characteristics are related to skeletal anatomy.

Monotremes are kind of evolutionary holdovers from the in-between species that split off from the mammal like reptiles of the late Permian and early Triassic.

They've probably lingered due in part to the isolation of Australia and in the platypus' case because it's electrolocation sense gives it an advantage that would be interlopers can't compete with. The bill can sense weak electric fields produced by the muscle contractions of buried crustaceans and insect larvae underwater.

The defining characteristics of mammals are hair, milk, our ear bones, and two distinct sets of teeth (milk teeth and adult teeth).

Answer 6

Like all other mammals, platypuses are covered in fur, lactate to feed their young, have four-chambered heart, a single bone in the lower jaws, three bones in the middle ear, and most importantly they are warm blooded. These are the characteristic of a mammals that the platypuses acquired.

Answer 7

Do Platypus Lay Eggs

Answer 8

The defining characters of a mammal are the presence of hair and females producing milk to feed offspring. Monotremes do this, even though they lay eggs.

Answer 9

They are mammals, but a special type called monotremes. They are still classified as mammals because their young drink milk.

Answer 10

they always lay eggs