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The Komodo dragon (Varanus komodoensis) is a monitor lizard native to the Lesser Sunda Islands of Indonesia. It is the largest extant species of lizard, growing to a maximum length of 3 m, and weighing up to 90 kg. Despite its large size, it occupies the smallest range distribution of any large carnivore in the world.

Komodo dragons spend most of their time in the hybrid zones between savannah and monsoon forest found at lower elevations. In the first year of their lives, they are primarily arboreal, preying on locusts and geckos, but as they grow larger, they become increasingly terrestrial. They have a powerful sense of smell; like other reptiles, they use their tongue to carry scent particles to their Jacobson's organ.

Komodo dragons exhibit a variety of feeding strategies: They can forage for small prey, ambush large prey like Javan rusa with an incapacitating bite, and scavenge on carrion. They primarily live an individual existence, but form small aggregations around carrion and kill sites in which they display a hierarchical system of feeding, where the largest individuals will eat first, leaving the scraps for smaller ones. Ritualized fighting and mating also usually occur in these aggregations. Larger Komodo dragons are willing to kill and eat smaller ones.

Mating typically occurs around June to August, with the eggs laid throughout the month of August. They incubate for about eight months and hatch around April or May, corresponding to the ending of the wet season when small prey is more numerous. Maturity is generally accomplished around 150 cm of length, or about 5 years of growth. It is estimated that in the wild, they may live up to 50 years.

Komodo dragons were first described by Western scientists in 1910, and since then, their rarity and fearsome appearance has made them popular in zoos. In the wild, their range has contracted significantly due to habitat changes caused by human activity. Because they prey on livestock and have been known to occasionally attack people, local people often try to hunt, trap, or poison them. They are listed as endangered by the IUCN Red List, and are protected under Indonesian law. A number of preserves in the area were founded to protect Komodo dragons, including Komodo National Park in 1980.

Nomenclature
In 1910, Lt. J.K.H. van Steyn van Hensbroek, the Civil Administrator in Reo on Flores, heard local stories of gigantic lizards on the nearby island of Komodo. Undertaking an expedition, he managed to capture and kill a 2.2 m long individual, sending a photograph of the specimen as well as its skin to Major Peter Ouwens, the director of the Zoological Museum of Bogor, Java. After procuring four more specimens, Ouwens first described the lizard in a paper published in 1912 as Varanus komodoensis. The common name "Komodo dragon" was coined by W. Douglas Burden in his 1927 book Dragon Lizards of Komodo: An Expedition to the Lost World of the Dutch East Indies, in which he recounted the 1926 expedition that captured two Komodo dragons and brought them alive to the Bronx Zoo.

Other common names for the Komodo dragon in English include the Komodo monitor or Komodo island monitor. It also has a variety of local names in Central Malayo-Polynesian languages, including but not limited to: ora in western Manggarai (which is spoken where Komodo dragons are most numerous), rugu in eastern and central Manggarai, sembe in Riung, and mbou in Bima. In Malay, it is referred to as biawak raksasa (giant monitor) or buaja darat (land crocodile).

Evolutionary history
Chromosomal studies suggest that the major extant lineages of the genus Varanus diverged about 40 million years ago in Asia, subsequently spreading out towards Africa, India, and Australia. Mitochondrial DNA analysis shows that the Komodo dragon is the closest relative (sister taxon) of the lace monitor (V. varius), and that their common ancestor diverged from a lineage that gave rise to the crocodile monitor (V. salvadorii) of New Guinea. Fossil and genetic evidence indicates that Komodo dragons evolved in Australia during the Pliocene about 3.8 million years ago, became widespread throughout the continent, and even hybridized with other species of monitor lizards there, and that they have changed very little compared to their current morphology. About one million years ago, they spread throughout the islands of Wallacea, which were connected to the mainland during the Pleistocene but eventually became isolated due to changes in sea level. Komodo dragons became extinct in Australia around 50,000 years ago, concurrent with the extinction of other megafaunal species such as their fellow giant monitor Megalania, and became reduced to the few remnant populations existing today.

It should be noted that this evolutionary history contradicts the former notion that Komodo dragons had evolved to their large size as a result of island gigantism. Instead of evolving from small ancestors who lacked competition from other predators within the islands, Komodo dragons arrived to the islands already massive and stayed the same size over time. It is thought that their large size allowed them to hunt the dwarf elephant Stegodon until they became extinct around 50,000 years ago, a niche that would not be replaced until the introduction of large ungulate prey by humans around 7,000-10,000 years ago. That Komodo dragons survived in the absence of large prey for tens of thousands of years is a testament to their physiological, behavioral, and ecological flexibility.

Description
Because of its reputation as a large lizard, estimations of the Komodo dragon's size have often been greatly exaggerated. The longest recorded specimen was a male at the St. Louis Zoo that measured 3.13 m from snout to tail tip. While 3 m long individuals are not unheard of in the wild, sexual mature Komodo dragons are at least 1.5 m long, and a length of 1.75 - 2 m is considered large. Their size varies dramatically based on their islands of origin: Komodo dragons from the larger islands of Komodo and Rinca have a snout-vent length up to 33% longer and a mass over 400% higher than those from the smaller islands of Gili Montang and Nusa Kode.

Komodo dragons that have not eaten weigh about 35 - 54 kg, but the largest wild Komodo dragons weigh around 70 kg, and weights as high as 81 kg have been recorded. The task of weighing Komodo dragons is complicated by the fact that they can consume up to 80% of their own weight in food. Including recently ingested food, it is quite possible for Komodo dragons to weigh past 100 kg.

The body plan of Komodo dragons is similar to that of other varanids, with long bodies, necks, tails, and limbs. However, their body proportions are flatter and more massive compared to smaller varanids. Throughout the lifespan of the Komodo dragon, the tail is slightly longer than the head and body, although this proportion lessens with age. Their hindlimbs are stout compared to their forelimbs, and all their toes bear long, recurved claws.

The coloration of Komodo dragons in different stages of their lifespans serve as cryptic coloration in different parts of its life. Young Komodo dragons have a speckled greenish-grayish appearance, which helps them blend in amidst the trees that they dwell in, but as they grow older, they adopt a uniform reddish clay color that suits their ground-dwelling nature. Larger Komodo dragons often have snouts that are speckled with metallic green, greenish-yellow, or yellowish-pink. As they mature, they also grow osteoderms beneath their scales throughout their bodies. The osteoderms in their head are particularly complex: Compared with other lizards, which have only one or two osteoderm shapes arranged in a simple pattern (if they have osteoderms at all), Komodo dragons have four distinct osteoderm shapes—rosette, platy, dendritic, and vermiform—arranged in a configuration resembling chain mail. The only areas lacking osteoderms on the head are the regions around the eyes, nostrils, mouth margins, and pineal eye, a light-sensing organ on the top of the head.

Komodo dragons have 7 premaxillary, 13 maxillary, and 12 mandibular teeth in their upper and lower jaws, for a total of 64 sharp, curved, serrated teeth that are well-adapted to slicing flesh. Their teeth are more laterally compressed than any other lizard, with a greatest-width-to-greatest-length ratio of 1:3.1. At least two-thirds of the tooth is sheathed in a thick, spongy layer of gum tissue, and when the Komodo dragon bites, the serrations on the tooth lacerate the gums, causing them to bleed and coloring the Komodo dragon's saliva pink or red.

Males are generally larger than females, with the latter rarely exceeding 2 m in length. At a glance, however, it is usually not possible to differentiate between males and females. One feature that only males have are a pair of small scale rosettes just anterior to the cloacal vent on either side of the midline, each of which enclose a little pit in a central scale. In juveniles, these pits may be filled with a waxy, yellowish-brown secretion plug, especially during the breeding season.

Senses
As with other varanids, Komodo dragons have only a single ear bone, the stapes, for transferring vibrations from the tympanic membrane to the cochlea. This arrangement means they are likely restricted to sounds in the 400 to 2,000 hertz range, compared to humans who hear between 20 and 20,000 hertz. They were formerly thought to be deaf because of their insensitivity towards soft and loud noises, but this was disputed by accounts of captive Komodo dragons responding to their keepers. In one example, a London Zoological Garden employee trained a captive specimen to come out to feed at the sound of her voice, even when she could not be seen.

Komodo dragons can see objects as far away as 300 m, but because their retinas only contain cones, they are thought to have poor night vision. They can distinguish colors, but have poor visual discrimination of stationary objects. As with many other reptiles, Komodo dragons are primarily scent oriented, relying on their long, yellow forked tongue to detect, taste, and smell stimuli with the vomeronasal sense using their Jacobson's organ. With the help of a favorable wind and its habit of swinging its head from side to side as it walks, a Komodo dragon may be able to detect carrion from 4 km away.

Distribution and range
Currently, Komodo dragons live in the islands of Komodo, Rinca, Gili Motang, and Nusa Kode, which are all part of Komodo National Park. They can also be found on the northern and western coasts of Flores, the largest island in the region where Komodo dragons can be found, although their range there has almost been halved since the first major population surveys done in 1979. Although Komodo dragons were present on Padar in 1979, they have not been found there for several decades, indicating the lack of a resident population there.

The Komodo dragon has the smallest current range of any large terrestrial carnivore known, with fewer than 3000 individuals living in an area of about 600 km2. However, it was formerly more widespread. The fossil record indicates that it originated from mainland Australia about 4 million years ago, dispersed throughout Wallacea 1 million years ago, before reducing down to its present range about 50,000 years ago.

Within their range, Komodo dragons inhabit a variety of habitats, from the shoreline to hilltops up to 700 m in elevation. However, they prefer xeric environments, in particular the monsoon forest, savannahs, and hybrid zones between them that occur at elevations under 500 m. These dryer, flatter regions allow for Komodo dragons to move more easily as they travel between resting and feeding sites, and are also conducive to the spread of windborne odors of potential prey or carrion. Komodo dragons are good swimmers, propelling themselves with their powerful tails, and have been observed swimming to offshore islets about 1000 m away, diving up to depths of 4 m. However, this is by no means a common activity, and they prefer to stay on land.

Feeding
Komodo dragons are carnivores and feed on a large variety of prey. Young Komodo dragons are arboreal and feed mostly on tree-dwelling geckos for the first eight months of their lives, transitioning to eating mostly grasshoppers and insects when the rainy season occurs. In the following dry season, when they are about a year old, they start to live mostly on the ground, and thus start hunting rodents and birds, such as green junglefowl, domestic chickens, and dusky megapodes, in addition to foraging for their eggs. As they reach full maturity, they start to become ambush predators of larger mammalian prey, such as wild boar, Javan rusa, and water buffalo. They have even been observed preferentially targeting pregnant members of such species in order to induce miscarriages, which has the double advantage of producing a fetus and afterbirth that can be consumed, as well as leaving the prey animal itself weakened for several hours. Other documented prey animals include snakes, Sunda porcupine, bats, shrews, crab-eating macaques, Asian palm civets, rats, hawksbill and green sea turtles (adults and eggs), horses, feral and domestic dogs, and feral and domestic goats. Larger Komodo dragons do occasionally practice cannibalism on smaller Komodo dragons that get in their way, particularly during periods of high population density.

Around 1 year of age, when Komodo dragons start to live mainly on the ground instead of the trees, they also start to scavenge for carrion, which is a mainstay of their diet. Using their powerful sense of smell, they can locate a carcass up to 4 km away. Although Komodo dragons are generally solitary, they will aggregate around carcasses in small groups. It is in this context that they exhibit a strict hierarchy based on size, where the largest individuals eat most of the carcass, leaving the smaller individuals to pick at the scraps. These smaller Komodo dragons may rub their bodies in the hair and intestinal contents of the carrion to cover themselves in that scent. It is thought that the unpleasant smell they acquire might protect them from cannibalism and assist them in relocating the carcass after being chased away by larger Komodo dragons.

When eating a large carcass, Komodo dragons will first start by ripping open the body wall and pulling out the stomach and intestines, slinging them side by side to rid them of their inedible contents. Then, they eat the thoracic diaphragm, lungs, heart, and other viscera first, followed by the rest of the body wall. Their jointed, flexible skulls, serrated teeth, high rate of salivation, and expandable stomachs are all adaptations that allow them to slice large chunks of flesh and swallow them whole. A group of four Komodo dragons can eat a large deer in 3-4 hours, or a large water buffalo in about 3-5 days. After swallowing, they will occasionally pause to wipe their faces in the ground. Very little of the carcass is wasted: Only about 12% by weight of a carcass is left uneaten by Komodo dragons, compared to 32-37% by tigers, which probably contributes to the lack of other scavengers in the Komodo dragon's range. Smaller prey is often swallowed whole headfirst without slicing, even up to the size of a 15 kg wild boar. Komodo dragons may eat up to 80% of their own body weight in a sitting, which can drastically inflate the recorded weight of certain specimens. This reflects a "feast-or-famine" survival strategy in the wild, in which Komodo dragons may only make 12 large kills in a year with smaller prey foraged in between, for an estimated annual consumption of 171 kg of food. In captivity, large Komodo dragons are only fed about 3 kg of meat a week to avoid obesity.

After feeding, Komodo dragons will seek out a sunny spot to bask and keep a high temperature in order to aid their digestion, lest their food putrefy in their stomach. Komodo dragons typically take about 3-6 days to digest their food, although the process may take longer if they are stressed or sick. Most of their food is digested, and whatever is indigestible—hair, teeth, hooves, feathers, or undigested bones—are disgorged in large gastric pellets, which are held together by a foul-smelling mucus. The process appears unpleasant to the lizards, and after disgorging, they will typically spend some time rubbing their faces into the ground and licking their lips to clean themselves. Fecal droppings are similar to that of other lizards, with nitrogenous waste expelled as white uric acid at the same time as the fecal matter.

Komodo dragons do not need to drink often, a useful adaptation given that surface water is generally unavailable during the 8-10 month long dry season. However, if water is available, they will drink deeply for a long time, particularly after large meals. When it drinks, it will immerse its snout up to its eyes, fill its mouth with water via buccal pumping in a similar matter to snakes, and tip its head backwards, allowing the water to run down its throat.

Although Komodo dragons are often referred to as apex predators in older sources, this designation is currently disputed because further research has shown that their presence does not significantly impact the population growth rates of its large mammalian prey, and because their population density is much higher than other apex predators. Because they are able to scavenge and take advantage of many different prey items, they have a much more generalist predatory role, which historically enabled their spread and survival from Australia to the Indonesian archipelago.

Bite
The Komodo dragon mainly aims to kill via directly induced bite trauma, using its serrated teeth to bite vulnerable areas, and then using its powerful neck muscles to violently thrash and shake prey to increase the severity of the wound and induce physiological shock. However, it is a subject of some controversy whether the Komodo dragon has other factors that aid in prey death.

In his 1981 study, Auffenberg observed that animals and humans bitten by Komodo dragons often had majorly infected bites. His hypothesis, which became known as the "bacteria as venom" model, posited that the Komodo dragon transmits virulent bacteria from its bite, resulting in a septic wound that cripples large prey who manage to survive the initial ambush. Moreover, Auffenberg believed that the Komodo dragon could also use its keen sense of smell to track prey with infected bite wounds. Indeed, 57 different species of bacteria have been identified from the saliva of wild and captive specimens, many of which are pathogenic, including Pasteurella multocida, which caused high mortality in mice injected with Komodo dragon saliva. However, this hypothesis had several major objections. First, although Auffenberg had observed prey animals with infected bites, neither him nor subsequent researchers ever observed Komodo dragons specifically tracking prey with infected wounds. Second, it was discovered that the oral microflora of Komodo dragons was largely shared with its environment, which would make infections incidental by nature rather than causal. In fact, it has been hypothesized in the "lizard-lizard epidemic model" that Komodo dragons may actually acquire pathogenic bacteria in an epidemic fashion from biting infected prey, who act as a disease vector for the bacteria, rather than prey acquiring the bacteria from their predators.

In 2009, the biologist Bryan Fry argued that the Komodo dragon, rather than using bacteria as venom, actually possessed venom glands in its lower jaw that could produce a variety of anticoagulant toxins, including Cysteine-rich secretory protein and kallikreins. This venom could be introduced into the bite through a "grip-and-rip" mechanism, in which the Komodo dragon's serrated teeth would create deep wounds for the venom to enter. However, Fry's definition of venom and venom glands was called into question by toxinologists, who did not see sufficient evidence to classify the Komodo dragon as venomous.

Although both the "bacteria as venom" and "venom" hypotheses do not have major support as possible mechanisms of killing prey, the existence of virulent bacteria in Komodo dragon saliva is still a topic of interest to pharmaceutical researchers, since Komodo dragons appear to be immune to such bacteria even after receiving bites from other Komodo dragons. Indeed, antimicrobial activity has been observed from Komodo dragons serum in vitro, and 66 different genes related to the innate immune system have been identified in the Komodo dragon genome.

Reproduction and life cycle
Although courtship behavior can be observed in Komodo dragons from January to October, copulation only occurs in a three-month period around June to August. It is believed that this extended courtship season aids in mutual recognition over time and pair bonding. Courtship and mating tends to occur around the aggregations of Komodo dragons that form around carrion and kill sites. During courtship, the male approaches the female from behind, flicking his tongue and pressing his snout against her hindquarters, which suggests some sort of pheromonal cue. He will then crawl over and on top of the female, scratching her back and sides with his claws and tonguing the area behind her ear, and attempt to mount her. Generally, the female will either run away or attack the male, so the majority of mounting moments are brief, with no attempt towards copulation on the part of the male. When copulation does happen, the female will raise the base of her tail in response to the male, which allows contact between their cloacae. The copulation process takes about twelve minutes. Young and inexperienced males have been observed to court and mount one another, an example of homosexual behavior in animals.

In the wild, Komodo dragons will lay their eggs throughout the month of August, with clutch sizes ranging from 1-30 eggs and an average of 18.5 eggs per clutch. In captivity, however, they may lay their eggs year round. These eggs are typically laid in unused orange-footed scrubfowl nests, around which the female will excavate other holes to act as decoys and prevent other Komodo dragons from eating the eggs. Females do not stay around to protect their nests.

The eggs have a soft, smooth, leathery shell, and have an average length of 86.6 mm, an average diameter of 55.5 mm, and an average weight of 124.7 g. After incubating for eight months, hatching occurs around April or May, corresponding to the end of the wet season when the density of insects and other small prey is at its highest. Hatching is an exhausting affair in which the hatchlings cut their way out of the egg with their egg tooth, which may take several attempts. At an average size of 304 mm, they are quite vulnerable to predation and make their way up into the trees, where they will spend the first year of their lives.

Komodo dragons become sexually mature when they achieve a length of about 150 cm, which takes about five to seven years of growth, given that males typically grow faster than females. While captive specimens have lived up to 20 years, it is thought that wild Komodo dragons may live up to 50 years.

Relationship with humans
Komodo dragons have shared a long history with hominids and modern humans. Homo floresiensis shared the same range as Komodo dragons for much of the Pleistocene until they disappeared around 50,000 years ago. Excavations at Liang Bua, a limestone cave on Flores, revealed that Komodo dragons were a prey item for H. florensis. Around the time that H. florensis disappeared, Homo sapiens arrived in Australia and Wallacea, where the Komodo dragon was widely distributed, and it is hypothesized that their presence led to the megafaunal extinctions around that time, including the contraction of the Komodo dragon's range down to its present remnant population. The introduction of domesticated ungulates like pigs, deer, and buffalo by humans aided the survival of these remnant populations, replacing large prey like Stegodon that had gone extinct thousands of years before.

Komodo dragons will generally ignore or flee from humans, but smaller ones are known to be more curious. However, they do enter human villages quite often, especially when they are hungry, because they are attracted by the smell of domesticated animals or drying fish. Because they have been known to dig up recently buried human corpses and eat them, Komodo residents make sure to tamp down graves with clay. It is thought that this behavior explains why Neolithic graves on Komodo took the form of low cairns above the gravesite, so that the rocks could also prevent Komodo dragons from digging up the remains.

Attacks on humans are very rare, but fatalities have been reported. Auffenberg's field study records the stories of six deaths that occurred from 1931-1980 as a result of Komodo dragon attacks, along with several anecdotes of attacks from interviewed villagers. In a 34 year period from 1974-2012, 24 people were attacked by Komodo dragons in Komodo National Park, with 5 fatalities. Most victims were local residents who were caught off guard, including an eight year old boy who was killed while playing in 2007 and a 31 year old man who was killed after falling out of a sugar apple tree in 2009.

Conservation
The Komodo dragon has been listed in the IUCN Red List as endangered species since 2021, an escalation from its previous classification in 1996 as a vulnerable species.