**Mammals** are species that can maintain a constant body temperature by generating their own heat when they are in a cooler environment, and by cooling themselves when they are in a hotter environment. They are four-chambered hearts, a closed circulatory system, and paired lungs for efficient respiration.

The three major subgroups of mammals are the following:

1. **Monotremes**: mammals that lay eggs, an example of which are spiny anteater and platypus.
2. **Marsupials**: mammals that have pouches in which the young spend most of the time during their development, an example of which is the kangaroo.
3. **Placenta**: mammals that have babies nourished by the placenta as they develop in the uterus, examples of which are dogs and cats.

The continental drift is the event in evolution in which the supercontinents moved in separate ways, resulting in convergent evolution where mammals evolve similar adaptations in form and functions due to similar environments.

See explanation.

A **placenta** serves as a channel between the mother and the fetus. Oxygen and nutrients pass through placenta from mother to the young. Waste products and carbon dioxide exit from the fetus to the mother via the placenta.

See explanation.

**Placental mammals** have babies nourished by the placenta as they develop in the uterus of the parent, In placental mammals, the embryo develops much longer inside the body of the mother, and as it passed birth it will be nourished through nursing.

There are **12 known orders of mammals** that exhibit placental development and they are:

1. Insectivores (examples: moles and hedgehogs)
2. Sirenians (example: Manatees
3. Chiropterans (example: bats)
4. Rodents (examples: squirrels, and rats)
5. Cetaceans (examples: narwhals, and whales)
6. Perissodactyls (examples: horses and zebras)
7. Xenarthrans (example: anteaters)
8. Carnivores (examples: dogs, and cats)
9. Artiodactyls (examples: giraffes, and antelope)
10. Primates (examples: chimpanzees, and gorillas)
11. Proboscideans (example: elephants)
12. Lagomorphs (example: rabbits)

**Lagormorphs** are mammalian species that are very similar to rodent species. These organisms have long ears and strong limbs that enable them to hop, leap and move efficiently. One distinguishing characteristic of these species from rodent species is that they have two pairs of large incisors in their upper jaw.

**Mammals** that feed on insects such as ants and termites evolved not just once but several times. These adaptations such as powerful claws, long, hairless snouts, and sticky tongues are products of evolutionary mechanisms to help them feed their prey and cope with their environment.