Question

With regards to reproduction, what 3 groups can mammals be classified in, based on modes of development and birth?

Answer 1

When we consider reproductive methods in mammals, they are classified as:
1. egg laying Monotremes,
2. pouched Marsupials, and
3. true Placentals.

Explanation:

Traditionally Class Mammalia is divided in two subclass:
Prototheria (includes egg laying mammals i.e. Monotremes), and
Theria (includes mammals which can give birth).

Subclass Theria is subdivided in two infraclass:
Metatheria (develop short-lived yolk sac placenta i.e. Marsupials), and
Eutheria (true placentals who develop chorionic placenta).

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