Biology · Animal Kingdom · NEET
Oviparous animals lay eggs and the baby grows inside the egg outside the mother's body. Viviparous animals do not lay eggs; the baby grows inside the mother and is born alive. The clue is in the name: 'ovi' means egg (like ovum), and 'vivi' means alive. So oviparous = egg-laying, viviparous = live-bearing.
No. This is the most tested trap. MOST mammals are viviparous, but a few egg-laying mammals exist. NCERT says mammals 'are viviparous with few exceptions'. The exception is Ornithorhynchus (Platypus), which is an OVIPAROUS mammal. So a statement like 'All mammals are viviparous' is FALSE in NEET. Say 'most mammals' not 'all mammals'.
The platypus (Ornithorhynchus) is OVIPAROUS. It is a mammal that lays eggs. NCERT lists it directly: 'Oviparous - Ornithorhynchus (Platypus)'. It is the classic exception used to break the 'all mammals give birth' rule. Remember this one animal and you can answer most exception-based questions.
All birds (class Aves) are OVIPAROUS. They all lay eggs; no bird gives birth to live young. NCERT states for Aves: 'They are oviparous.' This is why a NEET question can ask what feature birds and mammals do NOT share, and the answer is viviparity, because birds lay eggs while most mammals give birth.
Egg-layers (oviparous): fishes (Osteichthyes, mostly oviparous), amphibians, reptiles, and all birds (Aves). Live-bearers (viviparous): most mammals. Special notes: many cartilaginous fishes (Chondrichthyes, like some sharks) are viviparous, and the platypus is an oviparous mammal. So do not memorise it as 'fish always lay eggs' or 'mammals always give birth' — there are exceptions NEET loves.
In the Animal Kingdom chapter, NEET asks you to match features to classes (fish, amphibia, reptilia, aves, mammalia). Oviparity/viviparity is one of the grid features. Knowing that birds are oviparous, most mammals are viviparous, and the platypus is the exception lets you eliminate wrong options quickly in matching and 'always true' questions.
Which one of the following characteristics is not shared by birds and mammals?
Choose the correct statement.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Oviparous means egg-laying. The mother lays eggs and the young one develops inside the egg, outside her body. Examples: birds, most reptiles, most bony fishes, and the platypus.
Viviparous means giving birth to live young. The young one develops inside the mother's body and is born alive. Examples: most mammals including humans, and many cartilaginous fishes like some sharks.
Ornithorhynchus, the platypus. It is a mammal but it is oviparous (lays eggs). NCERT lists it as the oviparous example under Mammalia, and NEET uses it to break the 'all mammals are viviparous' statement.
Humans are viviparous. The baby develops inside the mother's uterus and is born alive. NCERT states clearly that humans are sexually reproducing and viviparous.
No. Most bony fishes (Osteichthyes) are oviparous, but many cartilaginous fishes (Chondrichthyes), such as certain sharks, are viviparous. NCERT notes that many chondrichthyans have internal fertilisation and are viviparous.
Oviparous means eggs are laid and hatch outside the mother. Ovoviviparous means eggs develop and hatch inside the mother's body, and then live young come out, but the embryo is nourished by the egg yolk, not by the mother directly. Pure viviparous animals nourish the embryo through the mother's body. For NEET Class 11 Animal Kingdom, focus mainly on oviparous vs viviparous.
