The largest known land lizard is probably Megalania at 7 metres (23 ft) in length.
However,maximum size of this animal is subject to debate. Megalania (Megalania prisca or Varanus priscus) is an extinct very large goanna or monitor lizard. They were part of a megafaunal assemblage that inhabited southern Australia during the Pleistocene. They seem to have disappeared between 40,000 and 30,000 years ago. The first aboriginal settlers of Australia might have encountered them.
The name Megalania prisca was coined in 1859 by Sir Richard 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.
Owen introduced the genus Megalania to accommodate the species Megalania prisca. Its status as a valid genus remains controversial, with many authors preferring to consider it a junior synonym of Varanus which encompasses all living monitor lizards. As the gender of the genera Megalania and Varanus are respectively feminine and masculine, the specific name prisca (fem.)/priscus (masc.) follows suit.
The genus Megalania is included as a synonym of Varanus by many researchers due to the relationships of the many Varanus species; M. prisca is closely related to other Australian monitors classified as Varanus, so excluding M. prisca 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.
Several studies have attempted to establish the phylogenetic position of megalania within the Varanidae. An affinity with the perentie, 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 Komodo dragon based on neurocranial similarities, with the lace monitor as the closest living Australian relative. Conversely, the perentie is considered more closely related to the Gould's and argus monitors.
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 7 m (23 ft), with a maximum weight of approximately 600–620 kg (1,320–1,370 lb). In 2002, Stephen Wroe considerably downsized Megalania, suggesting a maximum length of 4.5 m (15 ft) and a weight of 331 kg (730 lb) with averages of 3.5 m (11 ft) and 97–158 kg (214–348 lb). decrying the earlier maximum length estimate of 7 m (23 ft) as an exaggerations based on flawed methods. However in 2009, Wroe, along with other researchers revised upwards their estimates to at least 5.5 m (18 ft) and 575 kg (1,268 lb).
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 (Varanus varius), then it would have reached a length of 7.9 metres (26 ft), while if its tail-to-body proportions were more similar to that of the Komodo dragon (Varanus komodoensis), then a length of around 7 m (23 ft) is more likely. Taking the maximal 7 m (23 ft) length, he estimated a weight of 1,940 kg (4,280 lb), with a leaner 320 kg (710 lb) being average.
Megalania is the largest terrestrial lizard known to have existed. Judging from its size, it would have fed mostly upon medium to large sized animals, including any of the giant marsupials like Diprotodon along with other reptiles and small mammals, as well as birds and their eggs and chicks.It had heavily built limbs and body and a large skull complete with a small crest in between the eyes, and a jaw full of serrated blade-like teeth.
Some scientists regard with skepticism the contention that megalanias were the only, or even principal, predators of the Australian Pleistocene megafauna.They note that the "marsupial lion" (Thylacoleo carnifex) has been implicated with the butchery of very large Pleistocene mammals, while megalania has not. In addition, they note that megalania fossils are extremely uncommon, in contrast to Thylacoleo carnifex with its wide distribution across Australian Pleistocene deposits. Quinkana, a genus of terrestrial crocodile that grew up to 6m and was present until around 40,000 years ago, has also been marked as another apex predator of Australian megafauna.
It has been suggested that, if one were to reconstruct the ecosystems that existed before the arrival of the humans on Australia, it would be desirable to introduce Komodo dragons to represent megalania.
A study published in 2009 utilizing Wroe's earlier size estimates and an analysis of 18 closely related lizard species estimated a sprinting speed of 2.6–3 m/s (5.8–6.7 mph). This speed is comparable to that of the extant freshwater crocodile (Crocodylus johnstoni).
Along with other varanid lizards, such as the Komodo dragon and the lace monitor, megalania belongs to the proposed clade Toxicofera, which contains all known reptile clades possessing toxin-secreting oral glands, as well as their close, non-venomous relatives, including Iguania, Anguimorpha, and Serpentes.Being a member of Anguimorpha, megalania may have been venomous and if so, would be the largest venomous vertebrate known.
While there are occasional reports from Australia and New Guinea of giant lizards similar to megalania these reports only began after the species was first described and became publicly known. There is no credible scientific evidence of the existence of a surviving population.
Palaeosaniwa canadensis is an extinct species of carnivorous lizard from the late Cretaceous of North America. The name, given by Charles Whitney Gilmore in 1928, means "ancient Saniwa from Canada".
Palaeosaniwa was roughly comparable to a large monitor lizard (Varanidae) in size. Measuring around 3.5 meters or more in length it is among the largest terrestrial lizards known from the Mesozoic period (though Asprosaurus may compete with it in size). It is similar to modern varanid lizards (particularly the Komodo dragon) in having bladelike teeth with minute serrations. These teeth would have been effective for seizing and cutting large prey items, and suggest that Palaeosaniwa fed on other vertebrates. Adult Palaeosaniwa would have been large enough to prey on any of the birds or mammals known from the time, small dinosaurs, and the eggs and juveniles of large dinosaurs.
Palaeosaniwa is a member of the Platynota, a group that includes the monitor lizards (Varanidae) and Gila monsters (Helodermatidae). Originally, it was thought to be a member of the Varanidae, but has also been interpreted as a relative of the Helodermatidae.The most recent analysis places Palaeosaniwa outside of either Varanidae or Helodermatidae, as a stem member of the Varanoidea. Its precise affinities remain poorly understood, but it may be related to other Late Cretaceous, North American carnivorous lizards such as Parasaniwa, Paraderma, Labrodioctes, and Cemeterius.
Asprosaurus is an extinct genus of anguimorph lizard from the Late Cretaceous of South Korea. Named in 2015 from the Boseong Bibong-ri Dinosaur Egg Site, the type species Asprosaurus bibongriensis is the first Mesozoic lizard to have been discovered on the Korean peninsula. Because Asprosaurus is known only from fragmentary material, its relationships with other lizards are uncertain. However, features of the lower jaw suggest that it may be a member of a clade (evolutionary grouping) called Monstersauria, which includes the living Gila monster.Asprosaurus is noted for being a particularly large lizard species, measuring at an estimated length of 3-3.5 meters, a size comparable to the modern komodo dragon and the Cretaceous Palaeosaniwa. Alongside the latter, it is among the largest terrestrial squamates of the era, showcasing that these animals could grow to fairly large sizes in spite of competition from dinosaurs.
Estesia (in honour of Richard Estes) is an extinct genus of Late Cretaceous helodermatoid lizard found in the Gobi Desert in Mongolia. It was discovered in June 1990 by a joint expedition made up of Mongolian and American palaeontologists, and described in 1992 by Mark Norell, Malcolm McKenna and Michael Novacek. This animal is very interesting, not only because it's a close, albeit distant in time, relative to modern Gila monsters (Heloderma), but also because its dentition shows evidence that it was venomous. The type species is E. mongoliensis, after Mongolia, where it was found. It appears that it existed approximately eighty million years agо.
In the description, Estesia was assigned to Varanoidea, as the sister group to Varanidae, based on skull characters. However, the new material found in 1993 provided evidence that not only Estesia was not closely related to modern varanids, it was actually a distant relative of Gila monsters. The phylogenetic analysis presented by Norell and Gao (1997) actually supported the creation of a new group that included modern Gila monsters and extinct pre-historic forms, the Monstersauria.
The teeth of Estesia were sharp and recurved, like in modern varanoids. Interestingly, these teeth possess longitudinal grooves that run both from the anterior and posterior tooth surfaces during the entire tooth length. Similar characteristics are present in the teeth of Gila monsters. Because of the grooves, it is thought that this lizard was venomous, probably delivering venom in a manner similar to modern Gila monsters. It was 300 cm long.