Megalania - WikiHQ

Megalania  (Varanus priscus) is an extinct species of giant monitor lizard, The indigenous peoples of Australia might have encountered megalania when they first arrived on the continent and might have subsequently played a role 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

thumb|Illustration of the original dorsal and cervical vertebrae, 1859

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". which encompasses all living monitor lizards. The genera "Megalania" and Varanus are respectively feminine and masculine in grammatical gender and their specific names need to match them: 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. 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

thumb|Two size estimations of megalania compared to extant monitor lizards and a human

The lack of complete or nearly complete fossil skeletons has made it difficult to determine the exact dimensions of megalania. In 2002, Stephen Wroe considerably downsized megalania, suggesting a maximum total length of and a weight of with average total lengths 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 snout-vent length. The average snout-vent length of known specimens were around , and such individuals would have weighed up to . The largest vertebra (QM 2942) would have belonged to an individual with a snout-vent length of and weighed up to .

Palaeobiology

thumb|[[Paleoart|Life restoration]]

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 such as Diprotodon, along with other reptiles and small mammals, as well as birds and their eggs and chicks. It had heavily built limbs and body, a large skull complete with a small crest between the eyes, and a jaw full of serrated, blade-like teeth. 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 T. carnifex's wide distribution across Australian Pleistocene deposits. Quinkana, a genus of terrestrial crocodiles that grew up to and was present until around 40,000 years ago, has also been marked as another apex predator of Australian megafauna.

Komodo dragons, megalania's closest relative, are known to have evolved in Australia before spreading to their current range in Indonesia, as fossil evidence from Queensland has implied. If one were to reconstruct the ecosystems that existed before the arrival of the humans on Australia, reintroducing Komodo dragons as an ecological proxy of megalania to the continent has been suggested.

A study published in 2009 using Wroe's earlier size estimates and an analysis of 18 closely related lizard species estimated a sprinting speed of . This speed is comparable to that of the extant freshwater crocodile (Crocodylus johnstoni).

The scales of megalania would possibly be similar to those of their extant relatives, possessing a honeycomb microstructure and both durable and resilient to water evaporation.

Venom

thumb|right|Hypothetical megalania skull, at the [[Museum of Science, Boston]]

Along with other varanid lizards, such as the Komodo dragon and the Nile monitor, megalania belongs to the proposed clade Toxicofera, which contains all known reptile clades possessing toxin-secreting oral glands, as well as their close venomous and nonvenomous relatives, including Iguania, Anguimorpha, and snakes. Closely related varanids use a potent venom found in glands inside the jaw. The venom in these lizards have been shown to be a haemotoxin. The venom would act as an anticoagulant and would greatly increase the bleeding the prey received from its wounds. This would rapidly decrease the prey's blood pressure and lead to systemic shock. Being a member of Anguimorpha, megalania may have been venomous and if so, would be the largest venomous vertebrate known.

Extinction

The youngest remains of the species date to the Late Pleistocene, with the youngest remains possibly referrable to the species being a large osteoderm dating to approximately 50,000 years ago from the Mount Etna Caves National Park in central-eastern Queensland.