Megalania (Varanus priscus) was a giant monitor lizard that lived in Australia during the Pleistocene era. It was part of a group of large animals known as megafauna. Scientists believe Megalania was the largest land lizard that ever existed, but the incomplete remains found make size estimates uncertain. Most fossils suggest these lizards were about 2–2.4 meters (6.6–7.9 feet) long without their tails, though some individuals may have grown much larger, possibly reaching lengths of 4.5 meters (15 feet), 5.5 meters (18 feet), or even 7 meters (23 feet) overall.
Megalania likely had a lifestyle similar to the modern Komodo dragon (Varanus komodoensis), which may be its closest living relative. The most recent fossils of giant monitor lizards in Australia are about 50,000 years old. Early human populations in Australia may have encountered Megalania when they first arrived and could have contributed to its extinction. Initially, Megalania was thought to be the only species in its genus, but it is now classified within the Varanus genus, which includes other Australian monitor lizards.
Taxonomy
In 1859, Sir Richard Owen described the first known remains of megalania from three vertebrae found among a collection of mainly marsupial bones. These bones were purchased by the British Museum and collected from the bed of a tributary of the Condamine River, west of Moreton Bay in eastern Australia. Owen named the species Megalania prisca, meaning "ancient great roamer," in reference to the land-dwelling nature of the large lizard. The name was inspired by the Greek word ἠλαίνω (ēlainō), which means "to roam." The similarity to the Latin word lania (a feminine form of "butcher") has led to some incorrect translations of the name as "ancient giant butcher." However, Megalania is no longer considered a valid genus. Many scientists now classify it as a junior synonym of Varanus, the group that includes all living monitor lizards. The genus names Megalania and Varanus have different grammatical genders (feminine and masculine), so their specific names must match: prisca (feminine) and priscus (masculine).
Megalania is grouped within Varanus because its physical features suggest it is more closely related to some Varanus species than others. Excluding Varanus priscus from Varanus would make the genus an unnatural grouping. In 2004, Ralph Molnar noted that even if all Varanus species were divided into subgroups, Varanus priscus would still belong to Varanus because it is the current subgenus and genus name for all Australian monitors. Unless other Australian monitor species were placed in their own exclusive genera, Megalania would not be a valid scientific name. However, Molnar suggested that "megalania" could be used as a common name for Varanus priscus.
Several studies have explored where Megalania fits within the Varanidae family. Some research suggests a connection to the perentie (Varanus giganteus), Australia's largest living lizard, based on skull structure. A recent study proposes that Megalania is closely related to the Komodo dragon (Varanus komodoensis) due to similarities in skull features, with the lace monitor (Varanus varius) being the closest living relative in Australia. In contrast, the perentie is more closely related to Gould's monitor and the Argus monitor.
Size
Because many fossils are incomplete, scientists have had trouble figuring out megalania's exact size. Early estimates suggested the largest megalania could be about 7 meters long and weigh up to 600–620 kilograms. In 2002, Stephen Wroe significantly reduced these estimates, proposing a maximum length of 4.5 meters and a weight of 331 kilograms. He argued that the earlier 7-meter estimate was too high and based on incorrect methods. In 2009, Wroe and other researchers increased the estimate to at least 5.5 meters long and 575 kilograms.
In 2003, Erickson and others estimated that a large fossil, QM F4452/3, might have been about 2.19 meters long, based on the length of its femur. In 2004, Ralph Molnar used the size of dorsal vertebrae to estimate megalania's size. He found that average specimens were around 2.2 to 2.4 meters long and could weigh up to 320 kilograms. The largest vertebra, QM 2942, suggested an individual could be 3.8 meters long and weigh up to 1,940 kilograms.
In 2012, Conrad and others compared megalania to other Varanus species. They estimated that the braincase (BMNH 39965) likely came from an individual about 1.78 to 1.9 meters in precaudal length. The largest specimen they studied, AMNH FR 6304, suggested precaudal lengths of up to 2 to 2.17 meters. They also noted that megalania might have grown longer than 3 meters in precaudal length, as some modern Varanus species are 151 to 225% larger than average individuals.
Palaeobiology
Megalania was the largest land-dwelling lizard that ever lived. Based on its size, it likely hunted medium- to large-sized animals, including giant marsupials like Diprotodon, as well as reptiles, small mammals, birds, and their eggs. It had strong limbs and a sturdy body, a large skull with a small crest between the eyes, and a jaw filled with sharp, blade-like teeth.
Some scientists question whether megalania was the main predator of Australia’s Pleistocene megafauna. They point out that the marsupial lion (Thylacoleo carnifex) has evidence of hunting very large mammals, while megalania has no such evidence. Additionally, megalania fossils are rare compared to the widespread remains of T. carnifex. Another top predator, Quinkana, a type of crocodile that grew up to 6–7 meters (20–23 feet) long and lived until about 40,000 years ago, was also a major predator of Australian megafauna.
Komodo dragons, megalania’s closest living relatives, evolved in Australia before spreading to Indonesia, as fossil evidence from Queensland suggests. Scientists have proposed reintroducing Komodo dragons to Australia as a way to study the ecosystems that existed before humans arrived.
A 2009 study estimated megalania’s sprinting speed at 2.6–3 meters per second (9.4–10.8 kilometers per hour) by comparing it to 18 related lizard species. This speed is similar to that of the modern freshwater crocodile (Crocodylus johnstoni).
Megalania’s scales may have resembled those of its living relatives, with a honeycomb-like structure that is strong and resistant to water loss.
Megalania belongs to a group of lizards called Varanidae, including Komodo dragons and Nile monitors, which are part of a larger group called Toxicofera. This group includes all reptiles with toxin-secreting glands, such as iguanas, some lizards, and snakes. Some related varanids use venom in their jaws, which acts as an anticoagulant and increases bleeding in prey, leading to a drop in blood pressure and systemic shock. As a member of Anguimorpha, megalania may have had venom and could have been the largest venomous vertebrate known.
The youngest megalania remains date to the Late Pleistocene, with the most recent evidence being a large osteoderm (a type of bony plate) found in Mount Etna Caves National Park, Queensland, and dated to about 50,000 years ago. A study comparing the muscle structure of nine related lizard species to megalania’s ancestor, V. priscus, suggests that megalania’s limbs, posture, and muscle composition would have made it inefficient at outrunning early human settlers in Australia. Many other Australian megafauna species went extinct around the same time, possibly due to human activity or competition with humans.
Encounters between megalania and early Aboriginal Australians may have inspired stories of fearsome creatures like the whowie.