diaphragmA mammal's main breathing muscle, shaped like a dome. It separates the chest from the belly. When it tightens, air is drawn into the lungs.
furThe dense, soft hair that covers most mammals. It has two layers: oily guard hair on top keeps water off the skin, and thick underfur beneath holds in warmth.
gestationThe span for which a mother carries unborn young. An elephant's lasts from a year and a half to two years.
litterA set of brothers and sisters born together. The word is used most where three to eight young are born at once.
live birthArriving as a formed baby, with no egg to hatch from. Nearly all mammals are born this way. The platypus and the echidnas are the exceptions.
mammalA haired animal that suckles its babies. The name was coined in 1758 from mamma, the Latin word for breast.
mammary glandWhere a mother's milk is made. It is a modified sweat gland.
nurseTo feed newborn young with milk from the body. Every young mammal starts life this way, even the ones that hatch from eggs.
placentaThe organ that feeds a baby before it is born. It is joined to the baby by the umbilical cord. Mammals that have one are called placental mammals.
vertebrateA creature whose body is held up by a spine. Mammals, birds, reptiles, amphibians and fish are vertebrates.
warm-bloodedAble to keep a steady body heat in any weather. Birds are warm-blooded as well. Scientists call such an animal an endotherm.
weanTo end a youngster's milk feeding, bit by bit. Weaning is finished when the young animal no longer takes any milk.
Show all 36 terms (24 more)
Groups of mammals 12
batA mammal whose arms and hands have become wings. No other mammal can truly fly. Only the rodents have more species among the orders of mammals.
carnivoranA member of the order of cats, dogs and bears. The order has about 300 species. Seals, sea lions and the walrus belong to it too.
cetaceanAny whale, toothed or baleen, dolphins included. Porpoises are cetaceans too. A cetacean lives its whole life in water and breathes air through a blowhole.
lagomorphA rabbit, hare or pika. Lagomorphs look like rodents and are close relatives. They have four upper incisors where a rodent has two.
marsupialA mammal whose newborn shelters in a belly pouch. Kangaroos, koalas, wombats and opossums are marsupials. The young are born very small and do most of their growing while they nurse.
monotremeA mammal of the small group whose young hatch. Just five species are living: one platypus and four echidnas.
orderA rank of classification just below class. Mammals are one class. Rodents, bats and primates are three of its orders.
pinnipedA seal, sea lion or walrus. The name means fin-footed. Pinnipeds live mostly in water and come ashore to have their young.
primateA monkey, ape, lemur or human. Most primates have thumbs that can press against the fingers, which makes for a better grip.
rodentA gnawer, such as a mouse, squirrel or beaver. About 40 percent of mammal species are rodents. Their front teeth never stop growing, and the largest rodent is the capybara.
sirenianA manatee or dugong; a sea cow. Only three species of manatee and the dugong are alive today. All of them live in water and feed on plants.
ungulateA hoofed mammal such as a horse, deer or pig. Horses and rhinoceroses are odd-toed ungulates. Cattle, pigs, deer and giraffes are even-toed.
Teeth, food and body parts 12
antlerA bony branch that a deer grows new every year. Antlers are real bone. In most kinds of deer only the males grow them, and reindeer are the exception.
baleenRows of bristly plates in place of a whale's teeth. It is made of keratin. A baleen whale has no teeth and filters small animals such as krill out of the water.
canine toothA fang: the pointed tooth beside the front teeth. It is often the largest tooth in a mammal's mouth. The tusks of a walrus are canine teeth.
carnivoreAn animal whose food is mostly other animals. The name comes from Latin words that mean meat and to devour.
herbivoreAn animal with a diet of plants and no meat. Herbivore teeth are built for squashing and grinding.
hoofA toenail grown thick enough to walk on. It is made of keratin, the material of hair and nails.
incisorA front tooth with a thin edge for biting off food. The tusks of an elephant are incisors. A person has eight incisors, four above and four below.
molarA chewing tooth with a wide crown, set far back. Molar is from the Latin for millstone.
omnivoreAn eater with a mixed diet, part plant, part meat. Pigs and bears are omnivores.
ruminantA hoofed plant-eater that chews its food twice. Cattle, sheep, goats, deer and giraffes are ruminants. Swallowed food comes back up as cud to be chewed again.
trunkAn elephant's nose and upper lip grown into one. It can grasp, and it brings food and water to the mouth. A trunk has no bone in it.
tuskA tooth so long that it shows with the jaws shut. Tusks keep growing all through life.
How this list was compiled: Term list chosen for this site on 2026-10-12. Each meaning is written in our own words and was checked that day against the article on the term in the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Fur, Warm-blooded, Vertebrate, Mammary gland, Lactation, Viviparity, Thoracic diaphragm, Litter (zoology), Weaning, Gestation, Elephant, Placenta, Placentalia, Marsupial, Monotreme, Primate, Rodent, Capybara, Cetacean, Ungulate, Lagomorpha, Pinniped, Bat, Sirenia, Carnivora, Order (taxonomy), Incisor, Canine tooth, Molar (tooth), Carnivore, Herbivore, Omnivore, Ruminant, Hoof, Antler, Tusk, Baleen and Baleen whale; the word mammal against its entry in the English Wiktionary (https://en.wiktionary.org/). What all mammals share (hair, milk, three middle ear bones, a muscular diaphragm) was checked against the Animal Diversity Web of the University of Michigan Museum of Zoology (https://animaldiversity.org/accounts/Mammalia/), and hair, milk, warm blood, live birth and the teeth of plant-eaters and meat-eaters against BBC Bitesize (https://www.bbc.co.uk/bitesize/articles/zfm84xs, What are mammals?; https://www.bbc.co.uk/bitesize/articles/z4w3bdm, Why do animals have different teeth?). The fact after each meaning is from the same pages. The largest and smallest mammals named in the questions were checked against the Wikipedia articles Blue whale, Etruscan shrew and Kitti's hog-nosed bat. Licence: own work
How it works
This mammals vocabulary worksheet lists mammal, fur, warm-blooded, vertebrate, live birth, litter, placenta and five more terms down the left, with their meanings in another order down the right and an answer key as its last page.
Read the full guide
Groups of mammals
Set opens on What makes a mammal. The second set has marsupial, monotreme, primate, rodent, cetacean, ungulate, lagomorph, pinniped, bat, sirenian, carnivoran and order.
Teeth, food and body parts
The third set has incisor, canine tooth, molar, carnivore, herbivore, omnivore, ruminant, hoof, antler, tusk, trunk and baleen.
Three things that no other animals have: hair, milk that the mother makes for her young, and three small bones in the middle ear. Mammals are also warm-blooded and breathe air with lungs.
What are the three types of mammals?
Placental mammals, whose young grow inside the mother, fed through a placenta; marsupials, whose young are born tiny and go on growing in a pouch; and monotremes, which lay eggs.
What is the largest mammal?
The blue whale, which is also the largest animal known to have lived. The smallest mammals weigh about 2 grams: the Etruscan shrew is the lightest, and Kitti's hog-nosed bat is arguably the shortest.
Are humans mammals?
Yes. People have hair, feed their babies on milk and are warm-blooded. Humans belong to the order of primates, with the monkeys, the apes and the lemurs.