Question

Mammary glands are functional in male and female both, in order of
(a) Prototheria
(b) Metatheria
(c) Eutheria
(d) All of the above

Answer 1

Hint: Almost most of the animals from this group are extinct. The egg-laying monotremes are studied from fossils of the Cretaceous and Cenozoic periods. They’re constituted today by the platypus and a number of other species of echidna.

Complete answer:
Mammary glands are functional in males and females both, in order of Prototheria. They lay eggs like most non-mammalian vertebrates. Contrarily, they nourish their newborn with mammary gland secretions like all other mammals. They lack nipples, but the skin over  their mammary glands exude milk for his or her babies. The Prototheria are well known as monotremes, which genuinely means that they have a single hole for excretion and reproduction. This is similar to birds and reptiles. The mammary glands of Prototheria are altered sweat glands. Males in addition to females have useful mammary glands.

Additional information: Some significant characteristics of mammals are- 1. Mammals are warm-blooded animals and they give birth to new ones. 2. They are the most dominant form of animals present in almost every kind of habitat. 3. They have mammary glands that assist them to secrete milk to nourish their younger ones 4. Presence of area of the brain called Neocortex 5. Their skin has oil glands (sebaceous glands) and sweat glands (sudoriferous glands) . 6. The fur of hair all over the body which benefits animals adapt to their environment. 7. They are heterodont as they have different kinds of teeth. 8. Mammals also possess cervical vertebrae. 9. The skull is dicondylic. 10. The mammals respire through the lungs.
So, the correct answer is ‘(a) Prototheria’.

Note: The Prototheria is also similar to reptiles in some aspects of their skeletons. Notably, their legs are on the edges of their bodies instead of underneath them. This results in a reptile-like gait. There are only 3 rare species of Prototheria. These are the Australian platypus and a couple of echidna (spiny anteater) species of Australia and New Guinea.