Question

Unlike eutherians, both monotremes and marsupials

(A) lack nipples.

(B) have some embryonic development outside the uterus.

(C) lay eggs.

(D) are found in Australia and Africa.

Short answer

(A) The statement“lack nipples” is false.

(B) The statement “have some embryonic development outside the uterus” is true.

(C) The statement “lay eggs” is false.

(D) The statement “are found in Australia and Africa” is false.

Step-by-step solution

Class Mammalia

Vertebrates animals are classified under several classes, each with a different mode of survival. The class Mammalia includes animals that have hairy bodies, mammary glands for the offspring’s nourishment, and small ear bones.

Explanation of option ‘(A)’

The organisms of the class Mammalia are divided into three main groups; among these, the monotremes are organisms in which both male and female organisms have mammary glands, but nipples are absent.

Thus, marsupials are organisms that have nipples in their mammary glands.

Therefore, the given statement is false.

Explanation of option ‘(B)’

The different group of mammals has different modes for reproduction. In the case of eutherians, entire embryonic development occurs within the reproductive structure of the female.

In monotremes and marsupials, a part of the embryonic development occurs within the female body. Some development occurs externally; marsupial offspring develop in the external pouch of the mother, and monotremes develop within the egg.

Thus, the character mentioned in this option is commonly found in marsupial and monotremes but not in eutherians.

Therefore, the given statement is true.

Explanation of option ‘(C)’

In the class Mammalia, most of the organisms give live birth. An exception to this is found in monotreme organisms that lay eggs. This feature is absent in the other two groups; that is, marsupials and eutherians.

Thus, monotremes are the only mammals that have the ability to lay eggs.

Therefore, the given statement is false.

Explanation of option ‘(D)’

Eutherians are mammalian organisms that are found in almost every place of the world and are not restricted to any one continent. In contrast, marsupials and monotremes are mainly found in Australia.

Thus, the marsupials and monotremes are not found in Africa; they are only found in Australia.

Therefore, the given statement is false.