The Komodo dragon[4] (Varanus komodoensis), also known as the Komodo monitor, is a species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang.[5] A member of the monitor lizard family Varanidae, it is the largest living species of lizard, growing to a maximum length of 3 metres (10 ft) in rare cases and weighing up to approximately 70 kilograms (150 lb).[5]
Their unusually large size has been attributed to island gigantism, since no other carnivorous animals fill the niche on the islands where they live.[6][7] However, recent research suggests the large size of Komodo dragons may be better understood as representative of a relict population of very large varanid lizards that once lived across Indonesia and Australia, most of which, along with other megafauna, died out after the Pleistocene (as a result of human activity).[1] Fossils very similar to V. komodoensis have been found in Australia dating to greater than 3.8 million years ago, and its body size remained stable on Flores, one of the handful of Indonesian islands where it is currently found, over the last 900,000 years, "a time marked by major faunal turnovers, extinction of the island's megafauna, and the arrival of early hominids by 880 ka [kiloannums]."[1]
As a result of their size, these lizards dominate the ecosystems in which they live.[8] Komodo dragons hunt and ambush prey including invertebrates, birds, and mammals. It has been claimed that they have a venomous bite; there are two glands in the lower jaw which secrete several toxic proteins. The biological significance of these proteins is disputed, but the glands have been shown to secrete an anticoagulant. Komodo dragons' group behaviour in hunting is exceptional in the reptile world. The diet of big Komodo dragons mainly consists of Timor deer, though they also eat considerable amounts of carrion.[5] Komodo dragons also occasionally attack humans.[9]
Mating begins between May and August, and the eggs are laid in September. About 20 eggs are deposited in abandoned megapode nests or in a self-dug nesting hole.[5] The eggs are incubated for seven to eight months, hatching in April, when insects are most plentiful. Young Komodo dragons are vulnerable and therefore dwell in trees, safe from predators and cannibalistic adults. They take 8 to 9 years to mature, and are estimated to live up to 30 years.[5]
Komodo dragons were first recorded by Western scientists in 1910.[10] Their large size and fearsome reputation make them popular zoo exhibits. In the wild, their range has contracted due to human activities, and they are listed as vulnerable by the IUCN.[2] They are protected under Indonesian law, and a national park, Komodo National Park, was founded to aid protection efforts.
Evolutionary history
The evolutionary development of the Komodo dragon started with the genus Varanus, which originated in Asia about 40 million years ago and migrated to Australia, where it evolved into giant forms (the largest of all being the recently extinct Megalania), helped by the absence of competing placental carnivorans. Around 15 million years ago, a collision between Australia and Southeast Asia allowed these larger varanids to move back into what is now the Indonesian archipelago, extending their range as far east as the island of Timor. The Komodo dragon was believed to have differentiated from its Australian ancestors 4 million years ago. However, recent fossil evidence from Queensland suggests the Komodo dragon actually evolved in Australia before spreading to Indonesia.[1][21] Dramatic lowering of sea level during the last glacial perioduncovered extensive stretches of continental shelf that the Komodo dragon colonised, becoming isolated in their present island range as sea levels rose afterwards.[1][11] Extinct Pliocene species of similar size to the modern Komodo dragon, such as Varanus sivalensis, have been found in Eurasia as well, indicating that they fared well even in environments containing competition such as mammalian carnivores until the climate change and extinction events that marked the beginning of the Pleistocene.[22]
Genetic analysis of mitochondrial DNA shows the Komodo dragon to be the closest relative (sister taxon) of the lace monitor (V. varius), with their common ancestor diverging from a lineage that gave rise to the crocodile monitor (Varanus salvadorii) of New Guinea.[23][24][25]
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