Asked Apr 7, 2019

5a. Define each of the 3 categories of mammals:

  • Eutherians
  • Marsupials
  • Monotremes:

Expert Answer

Step 1

Mammals belong to the class Mammalia. They are the warm-blooded animals and rule the terrestrial ecosystem. They are the largest (like a whale) and the most intelligent animals (like humans) on the planet. They have some typical characteristics like the presence of backbone, four-chambered heart, hair, neocortex, and three middle ear bones. They also contain mammary glands to secrete milk and feed the young ones.

Step 2

Based on their mechanism of baby’s development, they are divided into three groups:

  1. Prototheria – They are also termed as monotremes. They are almost extinct now but are the only mammals that lay eggs. Only 5 species of them are alive now, which are, anteater, platypus, Tasmania, and New Guinea. They have a single hole, that is, through the same hole they lay eggs and pass out the waste products. They maintain their body temperature at 32°C.
  2. Marsupials – They are also termed as Metatheria. They are mostly found in Australia, with 200 species there alone. The examples of marsupials are kangaroos, opossums, and koalas. They contain pouc...

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