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The very smallest deer on Earth is the northern pudu (Pudu mephistophiles). Found mainly in South American rainforests, they are only about a foot tall at the shoulder, weigh about 20 pounds, and grow tiny pointed antlers. Pudus are energetic little animals that skip, jump, and play during both the day and night. Northern pudus are only slightly smaller than their near cousin, the southern pudu.

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The unusual tufted deer (Elaphodus cephalophus) hails from the forests and jungles of Myanmar and China. A small deer that only weights about 100 pounds, the tufted deer has a unique tuft of hair on top of its head. In addition to the usual complement of antlers, it also grows fangs that it uses to defend itself and battle others for a mate.

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There are 10 confirmed species of brocket deer; all live in south and central American or on the island of Trinidad. All brocket deer are small, but the little red brocket deer is tiny, with a reddish coat and white underbelly. Little red brocket deer live only in the Andes region of South America, where they come out only at night.

Muntjacs are fairly common Asian deer, but some species of muntjac are wildly rare. The Truong Son muntjac (Muntiacus truongsonensis) is so rare that it was thought to be extinct until 1997 when a specimen was discovered by scientists from the World Wildlife Federation, Vietnam’s Ministry of Agriculture and Rural Development, and Da Nang University. The Truong Son muntjac's cousin, the large-antlered muntjac (Megamuntiacus vuquangensis) was also rediscovered during the 1990s. These amazing finds are the result of intensive conservation and research work.

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The unique Chinese water deer (Hydropotes inermis) lack antlers — but makes up for them with canine tusks so big that locals have dubbed them the "vampire deer." The deer sometimes even use their tusks to fight off rival males. While they are native to Korea and China, Chinese water deer can also be found at an English deer park called Woburn Abbey.

The big, shaggy cervid known as Pere David's deer (Elaphurus davidianus) was native to northeastern and east-central China but became extinct more than 200 years ago. It has since been reintroduced in the wild.

Pere David's deer have quite the history. In the 1800s, the only known specimens were kept in the Emperor of China’s Imperial Hunting Park. A French clergyman, Père Armand David, received permission to transport a few back to Europe. Soon afterward, natural disasters hit, and the entire Chinese deer population disappeared, while those few in Europe were spared by Père David's conservation efforts.

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The hog deer (Axis porcinus) comes from India. With its short legs and stocky body, it moves very much like a pig — which explains the name. Hog deer are small and shy, and with their rolling gait, they're more comfortable going under obstacles than leaping over them. Another unique quality of the hog deer is their bark, which they use when frightened or as a warning cry to others that danger is near.

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While caribou (Rangifer tarandus) and reindeer are the same species, the name caribou is used in the United States while the name reindeer is common in Europe and Asia. Caribou are big deer, and they have been domesticated for centuries. Both males and females have large antlers. In 2015, the IUCN Red List designated caribou as vulnerable, which can only be made worse by fact that their arctic habitat is shrinking.

The tiny silver-backed chevrotain (Ragulus versicolor), also called the mouse deer, receives an honorable mention here — while not a true deer, it has many characteristics in common with deer species. The chevrotain was believed to be extinct until it was rediscovered in 2019. This amazing little animal has fangs and lives in the jungles of Vietnam. The chevrotain weighs only about 20 pounds and, not surprisingly, remains highly endangered.