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

Answered: 5a. Define each of the 3 categories of…

Biology 2e

2nd Edition

ISBN:9781947172517

Author:Matthew Douglas, Jung Choi, Mary Ann Clark

Publisher:Matthew Douglas, Jung Choi, Mary Ann Clark

Chapter29: Vertebrates

Section: Chapter Questions

Problem 13RQ: Squamata includes. crocodiles and alligators turtles tuataras lizards and snakes

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Question

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

Eutherians
Marsupials
Monotremes:

Expert Solution

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:

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.
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 pouches in their belly, termed as marsupium, to protect and sustain the younger ones. They maintain their body temperature at 35°C.
Eutheria – They are also termed as placental mammals. They dominate the planet and are found everywhere. They are Rodentia, Chiroptera, Carnivora, and cetartiodactyls. Their body temperature is maintained at 38°C and has a high metabolic rate. They have a separate opening at the bottom of the pelvis to give the birth to young ones. In them, the fetus is present in the uterus of the mother. The fetus is nourished by placenta until the birth.

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