Which Animals Are Mammals?

Mammals, in general terms, are animals with hair and mammary glands that give birth to young. The class of mammals (Mammalia) has evolved into an extremely diverse group of animals that includes a large group of species. A total of 5,500 species of mammals exist in about 125 families and 27–29 orders (the number of families and orders can be different depending on the authority). As a group, rodents (order Rodentia) are one of the most numerous and diverse groups of living mammals.

After the extinction of the dinosaurs about 65 million years ago, mammals diversified from a common ancestor into numerous species that we know today. Mammals are said to have a wider range and to be more adaptable than any other class of animals, with the exception of a few complex forms such as arachnids and insects.

If you wish to know more viviparous animals and mammals, then keep reading our article on differences between mammals and viviparous animals.

Mammals are not defined by just one or two characteristics, but by unique morphological features as well as a great deal of ethological complexity that makes each individual unique. Mammals exhibit the following characteristics:

• They all breathe air, even aquatic mammals. Mammals have two lungs, with or without lobes, depending on the species. They also have trachea, bronchi, bronchioles and alveoli prepared for gas exchange, and a vocal organ with vocal cords in the larynx. This enables them to produce various sounds.
  
  
• Mammals have a cerebral neocortex or highly developed brain that allows them to develop a variety of complex cognitive abilities.

• Compared to other animals, mammals have an extremely complex digestive system. The main feature that distinguishes them is the presence of an appendix or cecum.
  
  
• There are many mammals with horns. Sometimes they consist of a bony base, sometimes of a multilayered skin, and sometimes they have no bony base, as in the horns of rhinoceroses.
  
  
• Depending on the species, they have nails, hooves, or claws made of keratin.
  
  
• Mammals have mammary glands derived from sebaceous glands that produce milk, which is necessary for feeding their young.
  
  
• Their skin has a large number of sweat and sebaceous glands. Some of them have evolved into scent or venom glands.
  
  
• Almost all species develop some form of hair. Some species, such as whales, develop hair at birth that they shed as they mature.
  
  
• With the exception of monotremes, which have a simpler reptilian ear, they have three bones in the middle ear (malleus, incus, and stapes).

The class of mammals (Mammalia) is divided into three orders: the monotremes, the marsupials, and the placentals. The classical definition of mammals excludes some of the earliest mammals that evolved on Earth.

1. Monotremes: There are only five species of mammals that are monotremes, including the platypuses and the echidnas. These mammals lay eggs and are thus egg-laying. They have also retained a feature of their reptilian ancestors, namely the cloaca, where both the digestive and reproductive systems converge.
   
   
2. Marsupials: marsupials are mammals that are viviparous but have a very short placental development in which the mammary glands are located outside the uterus but inside the membranous sac, the marsupium.
   
   
3. Placental: last but not least, there are the placental mammals, which are also viviparous and complete their fetal development in the womb. When they leave it, they are completely dependent on their mother for protection and food.

Our list of mammals will help you get to know these animals better, although it is not as comprehensive as the 5,200 species of mammals that currently live on Earth. As you can see, they are all very diverse.

We will start with land mammals, some of them include:

• Mountain zebra ( Equus zebra)
• Cat (Felis silvestris catus)
• Dog (Canis lupus familiaris)
• African elephant (Loxodonta africana)
• Wolf (Canis lupus)
• Red deer (Cervus elaphus)
• Eurasian lynx (Lynx lynx)
• European rabbit (Oryctolagus cuniculus)
• Horse (Equus ferus caballus)
• Chimpanzee (Pan troglodytes)
• Bonobo (Pan paniscus)
• Bornean orangutan (Pongo pygmaeus)
• Brown bear (Ursus arctos)
• Panda bear or giant panda (Ailuropoda melanoleuca)
• Red fox (Vulpes vulpes)
• Sumatran tiger (Panthera tigris sumatrae)
• Tiger (Panthera tigris tigris)
• Reindeer (Rangifer tarandus)
• Mantled Howler Monkey (Alouatta palliata)
• Flame (Lama glama)
• The striped skunk (Mephitis mephitis )
• The European badger (Meles meles )

These aquatic mammals depend on the ocean and other marine ecosystems to survive. Marine mammals include animals such as dolphins, seals, whales, among others:

• Gray whale ( Eschrichtius robustus )
• Pygmy right whale ( Caperea marginata )
• Ganges dolphin (Platanista gangetica )
• Fin whale ( Balaenoptera physalus )
• Blue whale ( Balaenoptera musculus )
• Bolivian dolphin ( Inia boliviensis )
• La Plata dolphin (Pontoporia blainvillei )
• Baiji (Lipotes vexillifer)
• Araguaian river dolphin (Inia araguaiaensis)
• Bowhead whale (Balaena mysticetus)
• Dusky dolphin (Lagenorhynchus obscurus)
• Harbor porpoise (Phocoena phocoena)
• Amazon river dolphin (Inia geoffrensis)
• Indus dolphin (Platanista minor)
• North Pacific right whale (Eubalaena japonica)
• Humpback whale (Megaptera novaeangliae)
• Atlantic dolphin (Lagenorhynchus acutus)
• Vaquita (Phocoena sinus)
• Harbor seal (Phoca vitulina)
• Australian sea lion (Neophoca cinerea)
• Northern fur seal (Callorhinus ursinus)
• Mediterranean monk seal (Monachus monachus)
• Crabeater seal (Lobodon carcinophagus)
• Sea leopard (Hydrurga leptonyx)
• Bearded seal (Erignathus barbatus)
• Pied seal ( Pagophilus groenlandicus )

If you want to learn more about mammals that live in the sea, then do not miss our article on aquatic mammals.

Image: Harbor Seal

Monotremes are a group of highly specialized egg-laying predatory mammals. The group is less varied than the others and only includes these species:

• Platypus (Ornithorhynchus anatinus)
• Short-beaked echidna (Tachyglossus aculeatus)
• Sir David's long-beaked echidna (Zaglossus attenboroughi)
• Eastern long-beaked echidna (Zaglossus bartoni)
• Western long-beaked echidna (Zaglossus bruijni)

If you want to learn more about these mammals that lay egss, then do not miss out our article on Monotremes.

Image: Platypus

Marsupials give birth to relatively undeveloped young, which usually reside in pouches on the mothers' abdomens for some time. Of the 334 species currently known, about 70% live on the Australian continent (the mainland, Tasmania, New Guinea, and nearby islands). The remaining 30% are found in the Americas, most notably in South America, Central America, and on species native to North America, namely the Virginia opossum. Some species include:

• Common wombat ( Vombatus ursinus)
• Sugar glider (Petaurus breviceps)
• Eastern gray kangaroo (Macropus giganteus)
• Western gray kangaroo (Macropus fuliginosus)
• Koala (Phascolarctos cinereus)
• Red kangaroo ( Macropus rufus)
• Tasmanian devil ( Sarcophilus harrisii)

Image: Western Gray Kangaroo

Bats are the only mammals that can fly free. Several other mammals can glide or parachute, including flying squirrels and flying lemurs. Some species include:

• Geoffroy's bat (Myotis emarginatus)
• Common noctule (Nyctalus noctula)
• Meridional serotine (Eptesicus isabellinus)
• Western red bat (Lasiurus blossevillii)
• Giant golden-crowned flying fox (Acerodon jubatus)
• Hammer-headed bat (Hypsignathus monstrosus)
• Pipistrelles (Pipistrellus pipistrellus)
• Common vampire bat (Desmodus rotundus)
• Hairy-legged vampire bat (Diphylla ecaudata)
• White-winged vampire bat (Diaemus youngi)

Image: Red desert bat

If you want to read similar articles to Which Animals Are Mammals?, we recommend you visit our Facts about the animal kingdom category.