Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal. Like marsupials and most other mammals, monotreme young are larval and fetus-like, as the presence of epipubic bones prevents the expansion of the torso, forcing them to produce small young. COUNT 4
QSN1 What is the common mammal group that gives birth to live young? ANS1 viviparous QSN2 How many species of mammals lay eggs? ANS2 five species QSN3 Which mammal that has the bill of a duck lays eggs? ANS3 platypus QSN4 The platypus has sex chromosomes more related to which other non-mammal? ANS4 chicken