Mammals Diversity and Characteristics Quiz

Study Notes

Mammals are a diverse group of vertebrate animals characterized by several unique features. They are the only animals that produce milk to nourish their young, and all female mammals have glands that can produce milk. Mammals also grow hair at some point during their life, which helps to keep their body warm and may help them blend in with their surroundings.

There are over 5,500 species of living mammals, arranged in about 125 families and 27–29 orders. The rodents (order Rodentia) are the most numerous of existing mammals, with the most diverse lineages. In contrast, the order Tubulidentata is represented by a single living species, the aardvark.

Mammals can be found in every major habitat, from land to water. Their size ranges from a bat weighing less than a gram to the largest animal, the blue whale, which reaches a length of more than 30 meters (100 feet) and a weight of 180 metric tons (nearly 200 short tons). They have evolved to exploit every major habitat, including seas adjacent to all major landmasses.

Mammals are known for their adaptability. They are found on every continent and in every ocean, and they use every possible form of locomotion. Terrestrial species walk, run, jump, climb, hop, swing, dig, and burrow. Aquatic ones swim, shuffle, and dive. Some even fly.

Diet and behavior vary among mammals. Carnivores, such as jaguars, tigers, and polar bears, are top predators that generally live solitary lives. Herbivores, like deer and zebras, live in family groups for protection and more opportunities to breed. Omnivores, such as primates and rodents, are known for their high intelligence and large numbers.

Mammal bones, especially skulls, are used for identification and to work out the evolutionary history of each species. For example, the jaws of a house cat are more lion-like than wolf-like, while the teeth of horses and zebras look alike. The ear bones of mammals were once the jaws of prehistoric reptiles.

Mammals have a hinged jaw, a muscular diaphragm separating the heart and lungs from the abdominal cavity, and only the left aortic arch persists. Mature red blood cells in all mammals lack a nucleus, while all other vertebrates have nucleated red blood cells. Except for the monotremes (an egg-laying order of mammals comprising echidnas and the duck-billed platypus), all mammals are viviparous, bearing live young.

Mammals are worldwide in distribution and have been said to have a wider distribution and be more adaptable than any other single class of animals, with the exception of certain less-complex forms such as arachnids and insects. This versatility in exploiting Earth is attributed in large part to the ability of mammals to regulate their body temperature.