Question

Eutherian mammals are
(a) Oviparous
(b) Viviparous
(c) Ovoviviparous
(d) Both oviparous and ovoviviparous

Answer 1

Hint: Mammals are the most dominant animal which inhabits most environments of the world. They are mostly terrestrial and some of them are aquatic. The class Mammalia is divided into subclass Prototheria, Metatheria, and Eutheria.

Complete answer:
Eutherian mammals are viviparous animals, in which the fetus develops inside the uterus of the mother. They are also known as placental mammals due to the presence of the placenta inside the mother which helps to nourish the fetus. They have a characteristic feature like an external ear, a mammary gland at the abdomen or thoracic region, presence of corpus callosum, digestive and urogenital tract have a separate aperture, and young one borne in an advanced stage. Examples of Eutherian mammals are the rat, shrews, bat, whale, elephant, lemurs, whale, human being, etc.

Additional Information: Prototheria is an egg-laying mammal that shows the connecting link between reptiles and mammals. They have mammary glands without a nipple. They have hairy skin and external ears are absent. They do not have a scrotum and the testes lie in the abdominal region. The digestive and urogenital tract opens out through a single opening cloacal aperture. They do not have a placenta in the mother’s womb and eggs are covered with a calcareous shell. Examples are the spiny anteater and the duck-billed platypus.
Metatheria is a pouched mammal characterized by the presence of a pouch on the belly of females. In the pouch of a mother, an immature young one lay till the maturation which feeds on mother milk. They have mammary glands with the presence of nipples located at the abdomen. They have a scrotum in front of the penis. They have a separate opening for digestive and urogenital which is controlled by a common sphincter muscle. They have placenta but small in size as compared to eutherian. An example is kangaroo, koala, and opossum.
So, the correct answer is ‘Viviparous’.

Note: Eutherian mammals show an evolutionary relationship with Insectivora, Edentata, Chiroptera, Primates, Rodentia, Lagomorpha, Cetacea, Carnivora, Proboscidea, Artiodactyla, and Perissodactyla. The evolutionary relationship of Eutherian depends upon the dentition.