Bears are mammals from the Ursidae family and marsupials are also mammals that usually bear a pouch, like a koala and a kangaroo. According to Australian Museum, mammals are divided into three major groups, i.e., monotremes, marsupials, and placentals.
Two-thirds of marsupials live in Australia. On the other hand, bears live throughout the world, except in Australia and Antarctica.
Bears are classified as mammals due to being covered in hair, their spine, their warm blood, and the fact that the female bears feed their cubs with milk once they’re born.
Marsupials and mammals have some shared characteristics like being warm-blooded and covered with hair and having a uterus and a placenta. But they also differ in many ways.
This article explores why bears are mammals and not marsupials, as well as how to differentiate between mammals and marsupials.
Why Are Bears Mammals?
Bears are mammals because they are vertebrates, have mammary glands that feed their young, have a heart with four chambers, are hairy, have a big neocortex, and have three bones in their inner ear.
1. Mammals are Vertebrates.
Having a backbone inside the body isn’t exclusive to mammals. Other animals like reptiles, fish, and birds also have a backbone.
All animals with a backbone are vertebrates. Those without it are called invertebrates. The bear’s spinal cord is surrounded by bone and cartilage.
2. Bears have Mammary Glands
Mammary glands or breasts of mammals produce milk which is food for the young when they’re born. The milk production known as lactation happens after childbirth.
The number of mammary glands depends on the bear species. For example, the polar bears have four while the brown and the black ones have six.
3. Bears Have a Four-Chambered Heart
A four-chambered heart is a trait of most mammals, but also of reptiles. This heart is pivotal for the mammal’s respiratory system and survival.
It helps mammals breathe in oxygen and remove carbon dioxide. Oxygen goes to the heart from the lungs and from there to the rest of the body. Bears need plenty of oxygen to burn the fatty acids and sugars for the production of energy.
4. Mammals Have Hair or Fur
Humans have hair whereas bears have fur that has two layers, one is the oily hairs on top and the second is the thick underfur.
Bears’ fur can be of different colors and it depends on the species. It doesn’t just keep the bears warm, but also protects them from pathogens, injuries, etc.
Read More: Black Bear vs Brown Bear
5. Mammals Have a Large Neocortex
The cerebral cortex is part of the cerebral cortex (the outer layer of the brain) and manages the memory storing, conscious thought, coordination, balance, spatial reasoning, etc.
The brown bear was found to have the largest brain; however, the number of neurons was the same as in a cat whose brain is one-tenth of that of the brown bear.
Read More: Do Bears Eat Cats?
6. Mammals have Three Bones in their Middle Ear
Mammals have three bones in their middle ear and this is also the case in bears. It helps them hear well and survive.
Bears are known to have excellent hearing and can hear over long distances. Their frequency of hearing is much greater than that of humans and also more sensitive.
Related Article: Do Bears Attack Horses, Cows, or Sheep?
What Is the Difference between Mammals & Marsupials?
Mammals and marsupials differ in the fact that the mammal feeds their young with milk from their mammary glands outside their body whereas marsupials grow and nourish their young in a pouch located in the front part of the body.
According to Science ABC, mammals give birth in one of three ways: birthing developed offspring, laying eggs, or birthing at an early development stage.
Bears give birth to live young in January and the cubs usually weigh between eight and 17 ounces and are blind. The litter number ranges from 1 to 5 cubs.
On the other hand, marsupials birth small and underdeveloped young that crawl from the mother into the pouch. Most of the females have pouches where the fetus known as a joey is fed with milk and also urinates and defecates there.
The joey remains in the pouch until the juvenile stage.
What About Koalas?
Despite being commonly referred to as the koala bear because it reminds of a bear due to its round ears and black nose, koalas aren’t bears-they’re marsupials. This iconic Australian animal is an avid tree climber.
The koala got the tagline “bear” from the English-speaking settlers during the 18th century due to the koala’s bear-like appearance and behaviors. For example, many bears and koalas are adept tree-climbers.
According to National Geographic, the koala lives in the eucalyptus forests in the east and south of Australia. When it’s not sleeping, the koala is eating.
Their favorite is the eucalyptus tree. It’s both their food and habitat. Their digestive system works hard to break down the eucalyptus which is toxic and to extract the nutrients.
This marsupial is born tiny, blind, and furless. On the journey to the pouch, it uses its sense of touch and smell, sense of direction, and claws. Inside the pouch, koalas attach to the teats of the mom that swells in the mouth and gets fed until grown, around six to seven months.
It consumes only milk during this period.
Bears are mammals, not marsupials. Marsupials are a group of mammals and there are three groups of mammals. Bears and marsupials have certain shared characteristics but aren’t the same.
The bear has six of the seven features of mammals and marsupials also have some of these traits, but not all of them. Marsupials and mammals are similar because they’re both warm-blooded, feed their young with milk, and are furry.
However, the major distinction between them is that mammals give birth to live young which is fed outside the mother’s body whereas marsupials are born underdeveloped and fed into a section of the mom’s body known as the pouch.
Although koalas are often referred to as koala bears, they’re not bears, but marsupials. They have a pouch and are born underdeveloped. They’re native to Australia where there are no bears.
Stuart is the editor of Fauna Facts. He edits our writers’ work as well as contributing his own content. Stuart is passionate about sustainable farming and animal welfare and has written extensively on cows and geese for the site.