Why Are Bears Mammals?


Bears belong to the family Ursidae, with eight species living worldwide, and three species living in North America. I saw a comment on a video recently that asked if bears were mammals, and this made me wonder if they have all the mammalian characteristics.  

Bears are mammals and have six of the seven mammalian traits. Bears are vertebrates, they have mammary glands which they use to feed their live young, have a four-chambered heart, have hair, possess a large neocortex, and have three inner ear bones. Bears do not have sweat glands.

If you want to find out more about the characteristics that bears share with other mammals then please read on.

If you or someone you know loves bears then check out these great gifts on Amazon.

Bear cub

Is A Bear A Vertebrate?

The first characteristic that all mammals share is that they have a backbone inside their body. However, it is not just mammals that have a backbone. Other animals such as amphibians, reptiles, fish, and birds also have a backbone. The animals with a backbone are called vertebrates.

There is another group of animals which are called invertebrates. These are animals that don’t have a backbone inside their body. Some examples of these include earthworms, starfish, single-celled organisms, octopus, clams, insects, snails, and spiders.

Bears are classed as vertebrates as they have a backbone inside their bodies. The spinal cord of the bear is surrounded by cartilage or bone.

Does A Bear Have Mammary Glands?

The second characteristic that mammals share is having mammary glands. The name mammal is taken from the Latin word mamma, which means breast and was popularised by Carl Linnaeus, a Swedish botanist, and zoologist.

Mammary glands are used to produce milk which is fed to the young after birth. Birth of mammals is live, although the duck-billed platypus and the echidna give birth to eggs. Milk is produced in the mammary glands after childbirth and is called lactation.  

Bears produce milk within their mammary glands. Different species of bears have a different amount of mammary glands. Polar bears have four mammary glands, whereas the brown bear and the American black bear have six nipples. Bears produce milk to feed their cubs after birth.

Polar bear cubs can feed on their mother’s milk for up to 30 months, although this can also be as short as 18 months before they are fully weaned off milk. Brown bears usually nurse until they are five months old. Black bears are usually weaned off milk between six to eight months. The milk contains essential nutrients for bear in the early stages for them to grow healthy.  

Does A Bear Have A Four-Chambered Heart?

Mammals and birds all share another characteristic. The heart of a mammal or bird contains four chambers. Another animal that also has a four-chambered heart is a reptile. The crocodile shares the characteristic of having a four-chambered heart.

The four-chambered heart is essential for the respiratory system of mammals and for mammals to survive. Oxygen is needed to survive, but the waste product once the oxygen has performed its function is carbon dioxide. Carbon dioxide is expelled back into the air when mammals breathe out.

The respiratory system allows mammals to breathe in oxygen and expel carbon dioxide. Oxygen enters the lungs where the cells of the body transport it through the blood to the left ventricle of the heart. The left ventricle pumps oxygen-rich blood to the left atrium. It is then pumped through the arteries to the rest of the body. 

The other two chambers of the heart are the right atria and right ventricle. Oxygen-poor blood is received from the veins and is pumped to the lungs where the carbon dioxide is expelled.

The four-chambered heart which mammals possess is essential for their survival. Four-chambered hearts are essential for warm-blooded animals as they use up a lot of energy. Due to this, they require a lot of oxygen. The four-chambered heart is an efficient way of getting large amounts of oxygen into the body.

Bears do have a four-chambered heart. Bears need plenty of oxygen as it is needed to produce energy. The oxygen is used to burn sugars and fatty acids in their cells which produces energy. The energy is needed for everything they do including movement and keeping themselves at a steady temperature.

Brown bear

Do Bears Have Hair?

Another characteristic of a mammal is that they have fur or hair. The fur is generally used as a word when a mammal has very thick body hair. Humans have hair, but we wouldn’t call it fur, whereas other mammals which are covered, such as bears would be said to have hair.

Hair or fur consists of two layers. These consist of a layer of oily guard hairs on top and a thicker underfur.  

The guard hairs are longer and coarser than the underfur. The guard hairs are used to repel water from the skin and to block ultraviolet rays from the sun. Animals that have markings, such as jaguars, have these markings on the guard hair layer.

The thick underfur is also called down fur. The down fur is used to keep the animal warm and is made up of curly, wavy hairs.

Whales and dolphins also have hair, although some species only have hair follicles. Toothed whales usually lose their hair shortly after birth. Some species such as the humpback whale have hair their entire life, although only with a single hair coming out of each hair follicle.  

Bears do have a thick coat of fur. The hair on a bear can come in many different colors. Although you may think that brown bears only have brown fur, they can also have black, cinnamon, reddish-brown or yellowish-brown.  

Polar bears do appear white which allows them to blend into their icy environment, but their fur contains no white pigment. The fur of a polar bear is actually clear and hollow. Polar bears have black skin which allows them to keep warm from the sun.

Do Bears Have Sweat Glands?

Mammals are endothermic and need to regulate their temperatures, and one of the ways they do this is by sweating.

For humans, sweating is a way of regulating our body temperature so that we don’t overheat, although not all mammals do this the same way. Sweat glands produce sweat which is then carried away from the body by evaporation. This carries away the heat and makes us feel cooler.  

Humans aren’t the only mammals that sweat through their skin. Primates and horses also sweat through sweat glands.

Some other animals use different ways to expel heat from their bodies, such as panting. Dogs that have been running or playing can often be seen panting, and cats also do this when exceptionally hot. Panting allows them to get rid of heat through their mouth

Most mammals do not have sweat glands on their bodies in the same way that humans do, and so need to use these other ways to cool down.

Bears do not have sweat glands and so must use other ways of cooling down. Bears have a thick coat of fur which gets very hot in warm weather. They use other methods such as resting in shade, panting, which is something they share with dogs, entering into the cool water, and lying down with their stomachs touching the ground.

Although sweat glands are a mammalian trait this does not mean that bears are not mammals. 

Do Bears Have A Neocortex?

The brain is one of the most complex organs in a mammals body. The cerebral cortex is the outer layer of the brain and is used for functions such as movement, decision making, processing information from the senses, and in humans, speech. 

The neocortex is a set of layers of the cerebral cortex and it is the neocortex that controls motor commands, spatial reasoning, sensory perception, and conscious thought. The larger the neocortex, the larger the capacity for the mammal to control these.

 The neocortex also allows mammals to store memories, including past experiences and events.  

 The majority of brain cells are found in the neocortex and the cerebellum. The cerebellum is used for coordination, posture, and balance.

The neocortex looks different in different animals. Primates, humans, and other larger animals have grooves (sulci) and ridges (gyri). The grooves, ridges, and folds allow a large neocortex to fit inside a smaller braincase.

Smaller mammals like rodents do not have deep grooves and ridges. The neocortex on these animals is also much smoother.

In a study by Suzanaa Herculano-Houzel, a professor of psychology at Vanderbilt University, they found that brown bears have a cortex that weighs 222 grams.

It was found that a brown bear had 251 million neurons in their brains. Brown bears were the largest brains in the study, but although they had the biggest brains, the number of neurons (nerve cells) was found to be the same as a domestic cat. The domestic cat has a brain one-tenth the size of the brown bear. Non-neuronal cells were found to be ten times the amount of the cat.

Do Bears Have Three Middle Ear Bones?

The final characteristic that mammals possess is having three bones in the middle ear. The three small bones, called ossicles, conduct vibrations (sound) to the inner ear from the eardrum.

The three bones are called the hammer, the anvil, and the stirrup.

Once the vibrations are in the inner ear, the vibrations are converted into nerve impulses, which are sent to the brain. These three bones play a vital role in a mammal’s ability to hear.

With many animals relying on their sense of hearing to be able to hear both predators and prey, excellent hearing is essential for mammals to survive.

Bears do have the three small inner ear bones which help them to hear. Bears have excellent hearing and although it has not been tested over 200 yards, it has been observed that they can hear over great distances than they can see. 

A bears hearing has a greater frequency range than humans and is also over twice the sensitivity.

If you or someone you know loves bears then check out these great gifts on Amazon.

References and Sources

American Society of Mammalogists – Mammalian Species, Issue 145, 8 May 1981, Pages 1–7

American Society of Mammalogists – Mammalian Species, Issue 439, 23 April 1993, Pages 1–10

American Society of Mammalogists – Mammalian Species, Issue 647, 23 January 2001, Pages 1–11

Study – Dogs Have the Most Neurons, Though Not the Largest Brain: Trade-Off between Body Mass and Number of Neurons in the Cerebral Cortex of Large Carnivoran Species

https://www.frontiersin.org/articles/10.3389/fnana.2017.00118/full

Brown, Gary. The Bear Almanac : A Comprehensive Guide to the Bears of the World. Guilford, Conn., Lyons Press, 2013.‌

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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