How is the size of animals reduced over a series of generations? In other words what is the process by which, for example, a chameleon the size of your hand ends up being no bigger than the tip of your finger? We are talking about a fascinating evolutionary process called insular dwarfism which occurs when a mammal's gene pool is limited to a very small and secluded environment, primarily islands. And guess what, it's been taking place since the time of the dinosaurs. So how exactly does it work, and what creatures best exemplify this extraordinary condition?

Click through and size up the process known as insular dwarfism.

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Magyarosaurus -

Magyarosaurus is a genus of dwarf sauropod dinosaur from the Late Cretaceous period. Magyarosaurus inhabited Hateg Island, an offshore island in the Tethys Sea located in the region around modern-day Hateg in Romania.

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Rapetosaurus -

The island it inhabited led to Magyarosaurus becoming a product of insular dwarfism (also described as island dwarfism)—the process and condition of large animals evolving or having a reduced body size. Hateg's limited food supplies and lack of predators favored dinosaurs with a smaller body size. The Magyarosaurus was one of the smallest dinosaurs in the sauropod family, reaching only 20 feet (6 meters) in length. In contrast, Magyarosaurus' continental relative, Rapetosaurus, had an average body length of 39 feet (12 meters).

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Struthiosaurus -

Similarly, Struthiosaurus was a small dinosaur. It roamed the Ibero-Armorican, Australoalpine, and Hateg islands, also during the Late Cretaceous epoch.

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Edmontonia -

Struthiosaurus' continental relative was the broad, bulky, and tank-like Edmontonia. This dinosaur is named for the Edmonton Formation (now the Horseshoe Canyon Formation in Canada), where it was found.

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Telmatosaurus -

Hateg Island was also home to Telmatosaurus during the Late Cretaceous period. In another example of insular dwarfism, this dinosaur's modest dimensions measured on average 16 ft (5 m) in length and 1,300 lb (600 kg) in body mass.

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Hadrosaurids -

Meanwhile, back on the continent, Hadrosaurids, or duck-billed dinosaurs, were among the most dominant herbivores during the Late Cretaceous and towered over their smaller cousins.

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King Island emu -

The reduction in the size of animals as an evolutionary process continued long after the dinosaurs disappeared. The King Island emu was endemic to King Island, in the Bass Strait between mainland Australia and Tasmania. This now-extinct species was the smallest of all known emus, a fact that led scientists to conclude that the bird is a likely example of insular dwarfism.

Image: John Gerrard Keulemans (1842–1912)

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Emu -

The King Island emu's continental relative is the emu, Australia's largest native bird and the second-tallest living bird after the common ostrich.

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Brookesia minima -

Brookesia minima, also known as the dwarf chameleon, is endemic to Nosy Be, an island located just off the northwest coast of Madagascar.

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Brown Leaf Chameleon -

Most of the dwarf chameleon's continental relatives are far larger, including the brown leaf chameleon (pictured). But there is one exception. Hidden away in the elevated rainforests of northern Madagascar is Brookesia nana, also known as the nano-chameleon. This diminutive creature is the world's smallest lizard, its existence on the mainland somewhat defying the insular dwarfism process.

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Pygmy three-toed sloth -

The pygmy three-toed sloth, also referred to as the dwarf sloth, is endemic to Isla Escudo de Veraguas, a small island off the Caribbean coast of Panama. Isla Escudos de Veraguas is located farthest from the mainland, and began breaking up into small islands due to rises in sea levels 10,000 years ago. The pygmy three-toed sloth gradually became an independent species through insular dwarfism. The animal is assessed as Critically Endangered on the International Union for Conservation of Nature (IUCN) Red List.

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Brown-throated sloth -

The sloth's continental relative is the brown-throated sloth, the most common of the four species of three-toed sloth and widely distributed throughout the forests of South and Central America. It's approximately 40% heavier than the pygmy three-toed sloth.

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Megalocnus rodens -

Megalocnus rodens was a large ground sloth about the size of a black bear native to Cuba and Hispaniola during the Pleistocene and Holocene epochs.

Image: Havana Academy of Sciences

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Megatherium -

Megalocnus rodens' continental cousins however were far larger. In fact, Megatherium, a sloth species endemic to South America, was the size of an elephant.

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Pygmy mammoth -

The extinct pygmy mammoth was native to the Channel Islands off the coast of California. In a classic example of island dwarfism, the pygmy mammoth was descended from the colossal Columbian mammoth, whose domain was the Americas as far north as the Northern United States and as far south as Costa Rica.

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Columbian mammoth -

The Columbian mammoth was one of the largest mammoths to walk the Earth. It was also among the last mammoth species. The closest surviving relative of the Columbian and other mammoths is the Asian elephant.

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Palaeoloxodon falconeri -

Palaeoloxodon falconeri, or the Siculo-Maltese elephant, lived in Sicily and Malta during the Middle Pleistocene (around 500-200,000 years ago). Long extinct, P. falconeri was a species of dwarf elephant.

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Straight-tusked elephant -

Palaeoloxodon falconeri derived from a population of the mainland European straight-tusked elephant, which stood 13 feet, or 4 meters.

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Cozumel raccoon -

A species of raccoon named for Cozumel Island off the coast of the Yucatan Peninsula, Mexico, the Cozumel raccoon is listed as Critically Endangered by the IUCN. It's sometimes called the dwarf raccoon due to its diminutive size. The animals are, on average, about 18% shorter and 45% lighter than the subspecies of common raccoon found on the local mainland.

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Common racoon -

The common raccoon is the Cozumel's continental relative. It's native to North America.

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Japanese wolf -

Long extinct, the Japanese wolf was once endemic to the islands of Honshū, Shikoku, and Kyūshū in the Japanese archipelago.

Image: Philipp Franz von Siebold, 1850/ Special Collections of the University of Amsterdam

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Gray wolf -

The Japanese wolf's continental relative is the gray wolf. This large canine is native to Eurasia and North America.

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Tamaraw -

A bovid example of insular dwarfism is the tamaraw, or Mindoro dwarf buffalo. This small buffalo is endemic to the island of Mindoro in the Philippines, but its status is precarious, classified as Critically Endangered by the IUCN.

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Wild water buffalo -

The tamaraw's continental relative, the wild water buffalo, is itself endangered. It's currently found in small pockets in India, Nepal, Bhutan, Myanmar, Thailand, and Cambodia.

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Key deer -

This smallest extant North American deer species only lives in the Florida Keys. A rare species, key deer easily swim between islands and occupy nearly all habitats within their range, including pine rocklands, mangroves, and freshwater wetlands.

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White-tailed deer -

The white-tailed deer is the key deer's continental relative. It is native to North America, Central America, and South America.

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Svalbard reindeer -

Svalbard reindeer are endemic to the remote Norwegian islands of Svalbard, where they have lived for at least 5,000 years. Svalbard lies midway between the northern coast of Norway and the North Pole, and is noted for its particularly harsh climate. Fortunately, these small but robust reindeer are well adapted to the cold.

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Reindeer -

As the Svalbard's continental relative, reindeer or caribou are perfectly at home in the Arctic regions of Northern Europe, Siberia, and North America.

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Zanzibar red colobus -

The Zanzibar red colobus' home is Unguja, the main island of the Zanzibar Archipelago, off the coast of Tanzania. It's an endangered species, according to the IUCN's Red List.

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Udzungwa red colobus -

Back on the mainland, the Udzungwa red colobus represents the red colobus' continental relative.

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Homo floresiensis -

At just over 3 feet tall, or 1 meter, the ancient human species Homo floresiensis has been occasionally referred to as the real-life 'hobbit.' This archaic human is known as "Flores Man" after the island of Flores in Indonesia where this diminutive being lived until the arrival of modern humans about 50,000 years ago.

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Homo erectus -

Homo erectus—"upright man"—appeared during the Pleistocene, with its earliest occurrence about 2 million years ago. The last known population of H. erectus is H. e. soloensis from Java, around 117,000–108,000 years ago.