Bears are mammals.
Bears, regardless of their type, are classified as mammals by nature of several classifying features.
Definition and Classification of Mammals
There are some exceptional animals that are classified as mammals despite not meeting certain criteria, but bears meet all of them. Mammals are known for having sweat glands—specifically mammary glands, specialized teeth, hair, endothermy (or the ability to regulate their own temperature), a unique neocortex portion of the brain, red blood cells without nuclei, and a heart with four chambers. In addition, certain mammalian bones are used in classification, like the bones that meet to form the jaw and the three tiny bones known as the malleus, the incus, and the stapes, which form the middle ear. When asking if any animal is a mammal, it is necessary to understand that the definition extends beyond what is commonly thought of as just being warm-blooded or mammalian mothers nursing their young.
Different Groups of Bears as Mammals
The animals that we commonly think of as bears are not necessarily all related in the same ways, but all are mammals. While the koala bear isn’t technically a bear it, also, is a mammal. You can refer to a koala as a marsupial mammal, while other bears are placental mammals. Any other species of bear you might refer to (e.g., black bears, polar bears, Asian bears, sun bears) is found in the Ursidae family and has in common the same general characteristics of mammals referred to above.
Rowe, Timothy. “Definition, Diagnosis, and Origin of Mammalia.” Journal of Vertebrate Paleontology. N.p., n.d. Web. 1 Nov. 2012. http://www.geo.utexas.edu/faculty/rowe/Publications/pdf/010%20Rowe%201988.pdf
“American Black Bear.” Animalias.com. N.p., n.d. Web. 1 Nov. 2012. http://www.animalias.com/baribal-1980
“Mammal Species of the World – Browse: Ursidae.” Welcome to Bucknell || Bucknell University . N.p., n.d. Web. 1 Nov. 2012. http://www.bucknell.edu/msw3/browse.asp?id=14000939