Teaching Vertebrates: Key Traits of Mammals

Mammals are a special group of creatures with some unique features. Mammals are a huge and diverse group of animals. They live on land, in freshwater, in oceans, and even take to the skies! They come in all sizes, from tiny creatures like the bumblebee bat to giants like whales. Mammals might seem very different from one another, but they share some special traits that help us distinguish them from other animals.

Mammals are part of a bigger category of animals called vertebrates, which means they all have a backbone. There are seven different groups, or classes, of vertebrates on Earth. These include amphibians, birds, mammals, reptiles, and three kinds of fish. In this post, we’ll learn more about the traits that make mammals unique from their other vertebrate relatives.

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Produce Milk

First, female mammals produce milk to feed their young. This trait is unique to mammals: none of the other vertebrate groups make milk. Milk comes from special mammary glands in female mammals only.

Since mammals nurse their young, the mother must stick around after a baby mammal is born. For this reason, mammal mothers are very involved parents. Parental care is taken to the extreme in a sub-group of mammals called marsupials (e.g., kangaroos and opossums). Not only do they nurse their babies, but they also carry them around in a special pouch or on their backs or bellies.

Other types of mammals called placentals and monotremes don’t carry their babies around. Instead, some hunker down in a den or burrow with their newborn babies. For example, foxes and bears give birth to their babies in dens. Other mammal babies, like horses and elk, are born ready to start walking and even running. Though mammal babies vary in their abilities and needs, they all require milk from their mothers.

Breathe Air With Lungs

Third, all mammals breathe air through their lungs – even the mammals that live in water must come to the surface to breathe. Despite their excellent swimming skills, whales, otters, seals, manatees, dolphins, and walruses are all mammals and come to the surface to breathe air.

However, these animals can all hold their breath for much longer than you or me. While a human might be able to hold their breath for about a minute, some marine mammals can hold their breath for an hour or more! For example, an elephant seal can hold its breath for up to two hours! However, if they cannot get to the surface to breathe for some reason, a seal (or any mammal) can drown. They do not have gills like fish and sharks.

Hair or Fur

Mammals must have hair or fur on some part of their body for at least part of their lives. You might be saying “Now wait a minute… what about marine mammals like whales?” Even marine mammals that appear hairless, like whales, are born with sensory hairs (whiskers) on their faces. Some species of whales lose these whiskers as they grow older.

From the sensory whiskers of a whale to the thick fur of a polar bear, there’s a huge variety of hairstyles among mammals. Hair and fur may serve several different purposes. Often hair and fur are for staying warm, especially among animals that live in temperate and polar climates. In warmer places, hair and fur help protect a mammal’s skin from intense sun. Hair and fur may also have patterns that help an animal camouflage.

Warm-blooded

Mammals are warm-blooded (also known as endothermic), which means they make their own body heat and maintain a constant temperature. Mammals are not the only vertebrates that are warm-blooded. Birds and even some fish are warm-blooded too.

You may be wondering: what does it mean to be warm-blooded? Warm-blooded animals make enough body heat to keep a relatively constant body temperature. For example, most humans maintain a constant body temperature of around 98°F (37°C). This takes a lot of energy, which comes from eating food.

Many warm-blooded animals have thick fur or feathers to help insulate their body – the same way a thick sweater keeps you warm by trapping your body heat. If a warm-blooded animal gets too warm, it may sweat or pant to cool off. Can you think of any mammals that sweat or pant?

Skeletal Features

Finally, mammal skeletons have some key characteristics. You already know that mammals are vertebrates, which means they have a backbone. Additionally, mammals always have hinged jaws with a single lower jawbone. All mammals also have three tiny ear bones, sometimes called the hammer, anvil, and stirrup.

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