The different types of mammals are classified into 21 groups including aardvarks, anteaters, bats, carnivores, cetaceans, elephants, marsupials, monotremes, primates, rodents, treeshrews and many others. This article explores mammal classification in order to better understand their diversity and common characteristics.
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Aardvarks (Tubulidentata) are burrowing, nocturnal placental mammals. There is only one living species in the group. The aardvark has a long snout, arched back and coarse fur. Their diet consists of primarily ants and termites, which it procures by tearing open the insects' nests with its long claws. Aardvarks inhabit savannas, woodlands and grasslands in sub-Saharan Africa, a range that extends from southern Egypt to the Cape of Good Hope. The closest living relatives to the aardvark includes cetaceans and the even-toed hoofed mammals.
The key characteristics of aardvarks include:
- distinct arch to the back
- sparse, coarse hair covering body
- four toes on front feet, five toes on hind feet
- each toe has a tough and claw-like nail that is well-suited for digging
- elongated head, disc-shaped snout tip
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Armadillos, Sloths, and Anteaters
Armadillos, sloths, and anteaters (Xenarthra) are a group of placental mammals that includes anteaters, armadillos and sloths. Anteaters are native to South America and one species, the armadillo, inhabits the southern United States. There are about 29 species of anteaters and their relatives alive today. Anteaters and their relatives are diverse in form. They are notable for the unique joints in their backbone which provide them with the strength and support they need to dig and burrow. The closest living relatives to the anteaters and their relatives are the pangolins.
The key characteristics of armadillos, sloths, and anteaters include:
- insectivores and herbivores
- lack incisors or canine teeth
- molars and premolars (when present) are cylindrical and lack enamel
- teeth have a single root
- unique joints in the lumbar vertebrae
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Bats (Chiroptera) are the only group of mammals that have wings. Although some other groups of mammals, such as flying lemurs, are able to glide using skin membranes, only bats are capable of true flight. There are 997 species of bats alive today. Bats include two basic groups, the megabats and microbats. There is some controversy over just how closely the megabats and microbats are related, with some scientists arguing that the two groups are differ markedly in brain structure. The closest living relatives to bats are colugos, followed by tree shrews and primates.
The key characteristics of bats include:
- only group of mammals that aer capable of powered, sustained flight
- front limbs are modified into wings
- thin membrane that extends between fingers on front hands and attaches to body and hind legs to form wings
- some species use echolocation for navigation
- diet varies among species (insects, fruit, nectar, small animals)
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Carnivores (Carnivora) are a group of mammals that consists of about 250 species. Carnivores first appeared during the Cenozoic, after the decline of the dinosaurs. The earliest carnivores were weasel-like creatures. During the Palaeocene, carnivores diverged into two lineages, feliforms and caniformes. Feliforms include cat-like carnivores such as hyenas, cats, civets, linsangs, mongooses and the fossa. Caniforms include dog-like carnivores such as dogs, red pandas, wolves, foxes, coyotes, bears, racoons, mustelids, aardwolves and wolverines.
The key characteristics of carnivores include:
- powerful, sharp claws
- enlarged carnassial teeth
- molars and premolars with sharp edges
- simple stomach
- at least four toes on each foot
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Cetaceans (Cetacea) are marine mammals that include toothed whales and toothless, filter-feeding baleen whales. There are about 88 species of cetaceans. Toothed whales are the more diverse of the two groups of cetaceans, with about 73 species. Toothed whales include dolphins, porpoises, sperm whales, beaked whales and killer whales. Baleen whales include about 15 species such as right whales, bowhead whales and rorquals. Cetaceans are highly-specialized mammals with sparsely-haired bodies, flipper-like forelimbs and reduced back limbs located within the body wall.
The key characteristics of cetaceans include:
- breath air through blowholes located at the top of the head
- higher myoglobin concentration in muscles, an adaptation to remaining under water for long periods of time
- lack external ear parts
- all species are aquatic
- streamlined (fusiform) body
- vestigial hind limbs
- front limbs are flippers or paddle-like
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Colugos (Dermoptera) are large, tree-dwelling placental mammals that glide using a flap of skin that forms a sail-like surface between their outstretched legs. Only two species of colugos remain today, the Philippine flying lemur and the Sunda flying lemur. Colugos are nocturnal herbivores that feed on leaves, shoots, flowers and fruits. Colugos inhabit the tropical rainforests of Southeast Asia. Despite being placental mammals, colugos give birth to their young when the young are still somewhat undeveloped. In this respect, colugos resemble marsupials.
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Elephant shrews (Macroscelidea) are small, long-nosed insect-eating mammals native to Africa. There are about 12 species of elephant shrews alive today including the golden-rumped elephant shrew, checkered elephant shrew, four-toed elephant shrew, short-eared elephant shrew, dusky elephant shrew and several others. The classification of elephant shrews has often been a matter of debate. In the past, elephant shrews have been classified as close relatives of hoofed mammals, hares and rabbits, insectivores, and treeshrews.
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Elephants (Proboscidea) include two groups, African elephants and Asian elephants. There are two species of African elephants, the forest elephant and the savanna elephant. There is only one species of Asian elephant. The most notable characteristics of elephants include their large size, massive skull and long muscular trunk. Elephants first arose during the Eocene. They diversified into as many as 150 different species that inhabited Africa, Europe and the Americas. The closest living relatives to the elephants are the sirenians.
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Hares, rabbits, and pikas (Lagomorpha) are small terrestrial mammals that can be found in a diverse range of habitats on every continent except Australia and Antarctica. Lagomorphs have short tails, large ears, eyes that are positioned high on each side of the head, and narrow, slitlike nostriles that they are able to close completely.
Even-toed hoofed mammals (Artiodactyla) includes pigs, hippopotamuses, pronghorn, deer, camels, giraffe, okapi and cattle. There are 225 species of even-toed hoofed mammals alive today. The articles listed below provide information about the characteristics, classification and evolution of even-toed hoofed mammals.