Megalania (Varanus priscus) is an extinct species of giant monitor lizard,[1] 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 97–1,940 kg (214–4,277 lb), 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.[2] The first indigenous settlers of Australia might have encountered megalania,[3] and been a factor in megalania's extinction.[4][2][5] 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
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".[1] 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,[6][7] 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).[8]
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.[8]
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.[10] The most recent comprehensive study[9] 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
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.[7] 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).[11] 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),[12] decrying the earlier maximum length estimate of 7 m (23 ft) as exaggerations based on flawed methods. In 2009, however Wroe joined other researchers in raising the estimate to at least 5.5 m (18 ft) and 575 kg (1,268 lb).[13]
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 7.9 m (26 ft), while if its tail-to-body proportions were more similar to that of the Komodo dragon, then a length 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.[7]
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.[citation needed] 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.[8]
Some scientists regard with skepticism the contention that megalania was the only, or even principal, predator of the Australian Pleistocene megafauna.[14] They note that the marsupial lion (Thylacoleo carnifex) has been implicated with the butchery of very large Pleistocene mammals, while megalania has not.[citation needed] 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 6 m 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.[15][16] 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.[17]
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 2.6–3 m/s (9.4–10.8 km/h). This speed is comparable to that of the extantfreshwater crocodile (Crocodylus johnstoni).[18]
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.[19]
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.[20][21][22] 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.[13]
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.[2] A study examined the morphology of nine closely related extant varanid lizards and then allometrically scaled and compared them to V. priscus, found that the musculature of the limbs, posture, muscular mass, and possible muscular composition of the animal would most likely have been inefficient when attempting to outrun the early human settlers who colonised Australia during that time.[4] Considering many other species of Australian megafauna went extinct around the same time, either due to human predation or being outcompeted by them, the same can be assumed for megalania.
Confrontations between megalania and early Aboriginal Australians may have inspired tales of fearsome creatures such as the whowie.[7]
References
^ abcOwen R. (1859). "Description of Some Remains of a Gigantic Land-Lizard (Megalania Prisca, Owen) from Australia". Philosophical Transactions of the Royal Society of London. 149: 43–48. doi:10.1098/rstl.1859.0002. JSTOR108688.
^ abcPrice, Gilbert J.; Louys, Julien; Cramb, Jonathan; Feng, Yue-xing; Zhao, Jian-xin; Hocknull, Scott A.; Webb, Gregory E.; Nguyen, Ai Duc; Joannes-Boyau, Renaud (2015-10-01). "Temporal overlap of humans and giant lizards (Varanidae; Squamata) in Pleistocene Australia". Quaternary Science Reviews. 125: 98–105. Bibcode:2015QSRv..125...98P. doi:10.1016/j.quascirev.2015.08.013.
^Lydekker R. (1888). Catalog of the fossil Reptilia in the British Museum (Natural History) Cromwell Road S.W. Pt. 1: The Orders Ornithosauria, Crocodilia, Squamata, Rhynchocephalia, and Proterosauria. London: The Trustees. Cited in Molnar RE (2004). "The long and honorable history of monitors and their kin". In King, Ruth Allen; Pianka, Eric R.; King, Dennis (eds.). Varanoid lizards of the world. Bloomington: Indiana University Press. p. 45. ISBN978-0-253-34366-6.)
^ abcdMolnar, Ralph E. (2004). Dragons in the dust: the paleobiology of the giant monitor lizard Megalania. Bloomington: Indiana University Press. ISBN978-0-253-34374-1.
^ abcMolnar RE (2004). "History of monitors and their kin". In King, Ruth Allen; Pianka, Eric R.; King, Dennis (eds.). Varanoid lizards of the world. Bloomington: Indiana University Press. p. 588. ISBN978-0-253-34366-6.
^Wroe S, Myers TJ, Wells RT & Gillespie, A (1999). "Estimating the weight of the Pleistocene marsupial lion, Thylacoleo carnifex (Thylacoleonidae : Marsupialia): implications for the ecomorphology of a marsupial super-predator and hypotheses of impoverishment of Australian marsupial carnivore faunas". Australian Journal of Zoology. 47 (5): 489–498. doi:10.1071/ZO99006.((cite journal)): CS1 maint: multiple names: authors list (link)
^Bucklitsch, Yannick; Böhme, Wolfgang; Koch, André (2016-08-17). "Scale Morphology and Micro-Structure of Monitor Lizards (Squamata: Varanidae: Varanus spp.) and their Allies: Implications for Systematics, Ecology, and Conservation". Zootaxa. 4153 (1): 1–192. doi:10.11646/zootaxa.4153.1.1. ISSN1175-5334. PMID27615821.
