Why do echidna and platypus belongs to phylum mammalia and not to any other phylum?

Answer 1

Mammalia is not a phylum, but a Class. The phylum is Chordata.

Platypuses and echidnas are mammals because, like all mammals, they feed their young on mothers' milk. This is despite them being egg-laying mammals. The defining trait of a mammal is to have mammary glands, to produce milk for its young. The platypus and the echidna produce their milk from numerous glands over their underside, and the milk runs into grooves from which the young drink. This is unlike other mammals which have teats.

There are other reasons why echidnas and platypuses are classified as mammals, such as having skin, hair or fur, being warm blooded and breathing via lungs (not gills).

Most mammals are also characterised by the following anatomical features, which the echidna and platypus share:

- A flexible neck with seven cervical vertebrae

- Mammals also show enhanced neocortex development

- Sound is produced by the larynx (a modified region of the trachea)

- limbs are oriented vertically

- The mammalian heart has 4 chambers

- Internal temperature is generally high

- Egg development occurs in the uterus (excluding monotremata)

- They have sweat glands

- A single lower jaw bone

- Diaphragm

- Three bones for a middle ear

- Give birth to young alive

- Feeds milk to its young

- Has hair on its body