Ever wonder who made the dioramas in our mammal halls? Read all about the artists who created these wonderful scenes. Learn more >
There are many things that make mammals unique from other animals, but two important features are that all mammals have hair and all mammals nourish their offspring with milk. Most mammals give live birth, with the exceptions being the egg-laying monotremes: the duck-billed platypus, the short-beaked echidna, and the long-beaked echidna. Live birth also occurs in some reptiles and some fishes so it isn’t a unique mammalian character. Paleontologists rely on hard parts that fossilize and define a mammal as having a lower jaw that is made up of a pair of bones (the right and left dentary bones) that articulate with the right and left squamosal bones on the skull. In contrast, the lower jaws of nonmammalian vertebrates are composed of several bones and articulate with entirely different skull elements.
Whales and dolphins are mammals that are specially adapted to life in the ocean. They have smooth skin that is hydrodynamic, allowing them to swim more efficiently. While they might appear to be hairless, whales and dolphins do in fact have whiskerlike hairs around their chins.
According to Mammal Species of the World, 3rd Edition (Wilson and Reeder 2005), the most recent authoritative published checklist of modern mammal species, there are 5,416 different species of mammals. However, the exact number of recognized mammal species fluctuates as new species are described and as scientists make other taxonomic revisions.
The blue whale (Balaenoptera musculus) is not only the largest mammal, it is also the largest animal that has ever lived on Earth. Blue whales may reach a length of up to 100 feet and may weigh as much as 200 tons.
Kitti’s hog-nosed bat (Craseonycteris thonglongyai) weighs a mere two grams, making it the smallest species of mammal. Another common name for this endangered bat, found in the forests of Thailand, is bumblebee bat.
Our Mammal Department Resources Page has a list of books and web sites that might be helpful. When doing research on the internet, be sure to cite only reputable web sites. There’s a lot of misinformation out there! Also, be sure to check with the librarian at your school or local public library.