Why and how does a platypus lay eggs?

Answer 1

Why not? note that reptiles, dinosaurs, and birds all lay eggs. And the platypus is a Survivor of one of the earliest mammals.

The real question is why (and how) other mammals developed a uterus and began delivering live young.
"Platypuses" and another type of monotreme, the "Echidnas", are an infraclass of mammals found in Australia and New Guinea called "Monotremes" that lay eggs rather than giving birth to live young like placental mammals and marsupials.
As you can see, this site officially recognizes "platypuses" as the plural of platypus, although "platopi" is the logical result of Latin grammar.

Mammals evolved from reptiles, and at some point the transition was made from laying eggs, as reptiles do, to live birth which is the way most mammals reproduce. The platypus is considered to be a particularly primitive form of mammal which has retained some reptilian features to a greater degree than other mammals. That is why they lay eggs.

Answer 2

Platypuses lay eggs in order to reproduce, unlike most mammals which give live birth.

The platypus is a monotreme, or egg-laying mammal, just like the echidna, and quite unique to Australia. Platypuses lay eggs in a chamber at the end of a burrow dug into a riverbank or next to a creek.

Their young, once hatched, drink milk from glands on the mother's abdomen, rather than attaching to teats.

Answer 3

A platypus is a monotreme, a mammal that lays eggs.
This is probably due to its moist habitat.