Rodents (Rodentia) are a diverse group of mammals that consist of more than 2000 species. Species can be arboreal, fossorial (burrowing), or semiaquatic. Well-known rodents include mice, rats, squirrels, prairie dogs, porcupines, beavers, guinea pigs, hamsters, and capybaras. Other animals such as rabbits, hares, and pikas were once included with them, but are now considered to be in a separate order, the Lagomorpha. Most rodents are small animals with robust bodies, short limbs, and long tails. They use their sharp incisors to gnaw food, excavate burrows, and defend themselves. Most eat seeds or other plant material, but some have more varied diets. They tend to be social animals and many species live in societies with complex ways of communicating with each other. Mating among rodents can vary from monogamy, to polygyny, to promiscuity. Many have litters of underdeveloped, altricial young, while others have precocial (relatively well developed) at birth.


Seals and Sea Lions

Seals and sea lions (Pinnipedia) are a group of semi-aquatic marine mammals that include sea lions, fur seals, true seals and the walrus. Members of this group are also known as the fin-footed mammals and are characterized by clumsiness on land but great agility in the water.



Tree shrews (Scandentia) are a group of arboreal and terrestrial mammals that includes Madras trees shrews, northern tree shrews, large tree shrews, painted treeshrews and many others. There are about 19 species of mammals alive today.



Monotremes (Monotremata) are a unique group of mammals that lay eggs instead of giving birth to live young like other mammals such as placental mammals and marsupials. Monotremes include several species of echidnas and the platypus.



Pangolins (Pholidota) are a group of mammals that includes the Indian pangolin, Chinese pangolin, Sunda pangolin, giant pangolin, tree pangolin and others.



Primates (Primates) are a group of mammals that includes 356 species. Primates include prosimians, monkeys and apes. Primates inhabit tropical regions throughout Central America, South America, Africa, Madagascar and east and southeast Asia. They form complex social units and many species possess adaptations suited for life in the trees, including dextrous hands and a prehensile tail.



Hyraxes (Hyracoidea) are a group of mammals that includes the rock hyrax, the yellow-spotted hyrax, the western tree hyrax, and the southern tree hyrax. There are 8 species of hyraxes alive today.



Insectivores (Insectivora) are a group of mammals that include hedgehogs, moonrats, shrews, and moles. Insectivores are generally small mammals with nocturnal habits. There are about 365 species of insectivores alive today.



Marsupials (Marsupialia) are a group of mammals that give birth to their young at an early stage of their development. After their birth, the young crawl up the mother’s body and into the safety of her marsupium—a pouch located on the mother’s abdomen. Once inside the marsupium, the baby attaches to a nipple and nurses until it is large enough to leave the pouch and better fend for itself in the outside world.


Hares, Rabbits, and Pikas

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

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.


Odd-Toed Hoofed Mammals

Odd-toed hoofed mammals (Perissodactyla) includes horses and their relatives, rhinoceroses, and tapirs. There are 19 species of odd-toed hoofed mammals alive today. The articles listed below provide information about the characteristics, classification and evolution of odd-toed hoofed mammals.



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 they are quite undeveloped and in this respect the resemble marsupials.


Elephant Shrews

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.



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.



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.



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.



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.



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.


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.



Sirenians (Sirenia) are a group of group of aquatic mammals that includes dugongs, manatees and sea cows. There are 4 species of sirenians alive today.