The word Prototheria is formed from the Greek word protos meaning first and ther meaning mammal. Mammals that lay eggs are called ovipositors or prototheria. They live in Australia and New Guinea. Dr. Siddique Publications
(i) They are primitive egg-laying mammals. They are not immortal.
(ii) They lay eggs with a leathery covering. A newborn is born from an egg.
(iii) Newborns suck the mother’s milk. Because their mammary glands do not have nipples.
(iv) They have sharp lips, no teeth and no external ears.
(v) There is only one mucous membrane for excretory, reproductive and digestive system. Hence they are called monotrims.
Examples: Goose-billed Platypus (Ornithorhynchus anatinus), Short-billed Echidna (Tachyglossus aculeatus)