Question

How would you compare the reproductive patterns of monotremes, marsupials, and placental mammals?

Answer 1

Vertebrata is one of the subphylums of phylum Chordata. Vertebrates are divided into five classes i.e. aves, fishes, mammals, reptiles, and amphibians. Mammals can feed their young with the milk produced by their mammary gland. The presence of the mammary gland is an important characteristic of mammals that separates them from other classes. The class Mammalia can be further subdivided into monotremes, marsupials, and placental mammals.

Complete answer:
Monotremes are mammals that can lay eggs (oviparous), this is the primary difference between monotremes and other mammals. They are the more primitive animals of all the other mammalian orders (marsupials and placental). Therefore, they have much simpler body structures such as a primitive skeletal system. The shape of their jaw is very different from other mammals. Some examples of monotremes are Platypus, Echidnas, etc.
Marsupials birth their young prematurely. The young one remains in the mother's pouch (marsupium) and continues to develop. They also have multiple teats to provide sustenance to their young. Marsupials have a smaller skull. Corpus callosum, a nerve tract, is absent in both marsupials and monotremes. Examples of marsupials are Kangaroo, Koalas, etc.
Placental mammals have their young grow inside their womb. A placenta surrounds the growing fetus. This placenta nourishes and also removes the waste from the fetus’s body. The young one remains and develops inside the mother’s womb till it is time to give birth. While marsupials also have a placenta surrounding their young, the placenta is less developed. Hence, the young ones are birthed prematurely. Examples of placental mammals are elephants, humans, etc.
The main difference between all three Orders of mammals is how they give birth to their young ones.

Note: Mammals are not always terrestrial; they may live in water and land like a platypus or live their whole life in water like whales. Mammals have fur or hair covering their body (some species of whales lose their hair as they mature). Compared to other animals, mammals also possess more developed brains.