Question

What characteristics is used to classify a mammals as a Monotremes, marsupials or placental mammals
A. The environment in which it lives
B. How much hair or fur it has
C. The structure of it’s brain
D. The way in which it’s young one’s develop

Answer 1

Hint: Vertebrate animals under the class Mammalia are called mammals. Monotreme, marsupial, and placental mammal come under class Mammalia but some characteristics in monotreme, marsupials, and placental mammal are different.

Complete step by step answer:Monotremes are mammals which lays egg but like other mammals, they nourish their young ones with milk. Like other mammals, they are also warm-blooded animals having mammary glands to feed their young ones. Examples: Echidnas, Ornithorhynchus (Platypus).
-Marsupials are mammals that have a pouch to carry their young ones and have mammary glands to nourish their young ones. Marsupials carry their young until they developed fully. Examples: Macropus (Kangaroo), Tasmanian devil.
-Placental mammal carried their foetus in the uterus of the mother to a minimum period of time in comparison to other mammals. Like other mammals, they have also mammary glands to nourish their young ones. Examples: Human, Elephas(Elephant).
-Monotremes, marsupials, and placental mammal all different in terms of the type of method they care for their young ones.
Hence option D is correct.
The way in which its young ones develop is the characteristics are used to classify mammals as Monotremes, marsupials, and placental mammal.
Additional Information: Common Characteristics of Mammals
1. Presence of mammary glands
2. Take care of their young ones for maximum time than others
3. Mostly give birth to young ones
4. Warm blooded a animals
5. Mammals possess hair
6. Different types of teeth present in the jaw
7. Development is direct

Note: Some placental mammal is defined as mammals that have placenta to nourish their foetus which is wrong because marsupials also have placenta to nourish their fetus. Placental mammal and marsupials are both good examples of adaptative evolution.