Megalania (Varanus priscus) is an extinct species of giant monitor lizard, part of the megafaunal assemblage that inhabited Australia during the Pleistocene. It is the largest terrestrial lizard known to have existed, reaching an estimated length of 3.5 to 7 metres (11.5 – 23 ft), and weighing between , but the fragmentary nature of known remains make estimates highly uncertain.
Megalania is thought to have had a similar ecology to the living Komodo dragon (Varanus komodoensis). The youngest fossil remains of giant monitor lizards in Australia date to around 50,000 years ago. The first indigenous settlers of Australia might have encountered megalania, and been a factor in megalania's extinction. While originally megalania was considered to be the only member of the titular genus "Megalania", today it is considered a member of the genus Varanus, being closely related to other Australian monitor lizards.
Taxonomy
Sir Richard Owen described the first known remains of megalania in 1859, from three vertebrae amongst a collection of primarily marsupial bones purchased by the British Museum, collected from the bed of a tributary of the Condamine River, west of Moreton Bay in eastern Australia. The name "Megalania prisca" was coined in the paper by Owen to mean "ancient great roamer"; the name was chosen "in reference to the terrestrial nature of the great Saurian". Owen used a modification of the Greek word ἠλαίνω ēlainō ("I roam"). The close similarity to the Latin word: lania (feminine form of "butcher") has resulted in numerous taxonomic and popular descriptions of "Megalania" mistranslating the name as "ancient giant butcher." "Megalania" is no longer considered a valid genus, with many authors preferring to consider it a junior synonym of Varanus, which encompasses all living monitor lizards. As the genera "Megalania" and Varanus are respectively feminine and masculine in gender, the specific names agree: prisca (feminine) and priscus (masculine).
Megalania is included within Varanus because its morphology suggests that it is more closely related to some species of Varanus than others, so excluding V. priscus from Varanus renders the latter genus an unnatural grouping. Ralph Molnar noted in 2004 that, even if every species of the genus Varanus were divided into groups currently designated as subgenera, V. priscus would still be classified in the genus Varanus, because this is the current subgenus name, as well as genus name, for all Australian monitors. Unless other Australian monitor species were each also classified their own exclusive genera, "Megalania" would not be a valid genus name. However, Molnar noted that "megalania" is suitable for use as a vernacular, rather than scientific name, for the species Varanus priscus.
Phylogeny
Several studies have attempted to establish the phylogenetic position of megalania within the Varanidae. An affinity with the perentie (Varanus giganteus), Australia's largest living lizard, has been suggested based on skull-roof morphology. The most recent comprehensive study proposes a sister-taxon relationship with the large Komodo dragon (Varanus komodoensis) based on neurocranial similarities, with the lace monitor (Varanus varius) as the closest living Australian relative. Conversely, the perentie is considered more closely related to Gould's monitor and the Argus monitor.
Size
The lack of complete or nearly complete fossil skeletons has made it difficult to determine the exact dimensions of megalania. Early estimates placed the length of the largest individuals at , with a maximum weight of approximately . In 2002, Stephen Wroe considerably downsized megalania, suggesting a maximum length of and a weight of with averages of and , decrying the earlier maximum length estimate of as exaggerations based on flawed methods. In 2009, however Wroe joined other researchers in raising the estimate to at least and .
In a book published in 2004, Ralph Molnar determined a range of potential sizes for megalania, made by scaling up from dorsal vertebrae, after he determined a relationship between dorsal vertebrae width and total body length. If it had a long, thin tail like the lace monitor, then it would have reached a length of , while if its tail-to-body proportions were more similar to that of the Komodo dragon, then a length around is more likely. Taking the maximal length, he estimated a weight of , with a leaner being average.