Question

Write the distinguished features of Prototheria, Metatheria and Eutheria.

Answer 1

Hint: Mammals evolved in the Triassic period of the Mesozoic era. Found in a variety of habitats. Living mammals are classified into two subclasses: Prototheria and Theria.

Complete Answer:

Sl.No	Prototheria	Metatheria	Eutheria
1.	It includes egg laying mammals, in which egg are large yolky and shelled	It includes all mammals more closely related to marsupials than to placentals.	They are true mammals and females have mammary glands.
2.	Mammary glands are without nipples	Mammary glands lack nipples, but the skin over their mammary glands exude milk for their babies	Mammary glands with nipples.
3.	Gynaecomastia [Both male and female suckle the young ones] is found in these animals.	Only females have mammary glands and show parental care.	Only female have mammary gland and show parental care
4.	In prototherian all the three tract i.e Anus, Urinary tract, reproductive tract commonly open into Cloaca	In marsupials, the genital tract [including urinary tract and reproductive duct] is separate from the anus.	In Male anus is separate and the urinogenital duct is separate. But in females the urinary tract, reproductive tract and anus is separate.
5.	In Males testis are inside the body and scrotum is absent.	In Male, the scrotum is present in front of the penis.	In Male, the scrotum is present behind the penis
6.	Young ones are hatch from egg after incubation	The young are born immature and for further development takes place in mothers pouch.	The young develop inside the mother's womb.
7.	Eg: Ornithorhynchus or Duck billed Platypus. Tachyglossus or Echidna or Spiny anteater	Eg: Marsupial[ Kangaroo], opossum, wombats	Eg: Tiger, Man, Elephants and Rhinoceros.

Note: Mammals produce amniotic eggs which contain albumin, provide the embryo with water and protein, and an egg yolk that supplies the embryo with energy. The Chorion, amnion, and Allantois are membranes covering the developing embryo found only in amniotic eggs.