What is a Mammal?

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NGSS Performance Expectations

MS-LS1-1 Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells.

MS-LS1-2 Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.

MS-LS1-3 Use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells.

HS-LS1-2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.

The content and activities in this topic will work towards building an appreciation for the evolutionary and ecological significance of mammals.

Mammals are a group of vertebrate animals. Examples of mammals include rats, cats, dogs, deer, monkeys, apes, bats, whales, dolphins, and humans. Figure 6.2 shows some examples of mammals.

<p><strong>Fig. 6.2.</strong> (<strong>A</strong>) Epauletted fruit bat (<em>Epomophorus</em> sp.)</p>

Fig. 6.2. (A) Epauletted fruit bat (Epomophorus sp.)

Image courtesy of Bernard DUPONT, Flickr

<p><strong>Fig. 6.2.</strong> (<strong>B</strong>) Atlantic spotted dolphins (<em>Stenella frontalis</em>)</p>

Fig. 6.2. (B) Atlantic spotted dolphins (Stenella frontalis)

Image courtesy of Bmatulis, Wikimedia Commons

<p><strong>Fig. 6.2. </strong>(<strong>C</strong>) Bennett's wallaby (<em>Macropus rufogriseus rufogriseus</em>)</p>

Fig. 6.2. (C) Bennett's wallaby (Macropus rufogriseus rufogriseus)

Image courtesy of Noodle snacks, Wikimedia Commons

<p><strong>Fig. 6.2.</strong> (<strong>D</strong>) Modern humans (<em>Homo sapiens</em>)</p>

Fig. 6.2. (D) Modern humans (Homo sapiens)

Image courtesy of Victor, Flickr

Mammals are distinguished from other vertebrate animals by several unique features. All mammals produce and secrete milk from mammary glands to feed their offspring. They also have hair on their bodies, although some mammalian groups have less hair than others. Hair or fur helps mammals survive in cold climates by insulating their bodies.

Mammals are a diverse group of animals that includes between 5,000 and 5,500 species adapted to live in a wide variety of environments. The vast majority of mammal species live on land, although some, such as otters, seals, and dolphins, live in freshwater and ocean habitats. Bats are mammals that are capable of flying.

Mammals are arguably one of the most successful groups of vertebrate animals. Evolutionary adaptations have allowed mammals to survive in places like the cold polar zones and alpine mountain habitats where few other vertebrate animals can live. The success of mammals in colonizing the earth is perhaps best illustrated by one particular species capable of altering its environment on a global scale: the human.

The remainder of this unit will focus on marine mammals—mammals that live in or near the ocean. There are 128 known species of marine mammals. Marine mammals include whales, sirenians, pinnipeds, the marine otter, the sea otter, and the polar bear. Figure 6.3 shows some examples of marine mammals. There are also several groups of marine mammals that have gone extinct. These include marine sloths, marine bears, and an entire order of hippo-like mammals called desmostylians.