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Meiolania

Meiolania is an extinct genus of meiolaniid stem-turtle native to Australasia throughout much of the Cenozoic. Meiolania was a large turtle, with the shell alone ranging from 0.7–2 m in length. Four species are currently recognized, although the validity of two of them is disputed. Meiolania was first described as a species of lizard related to Megalania by Richard Owen towards the end of the 19th century, before the continued discovery of additional fossils solidified its placement as a kind of turtle.

History and naming
Early research Perhaps the first recorded discovery of meiolaniid remains stems from John Foulis, a doctor who lived on Lord Howe Island halfway through the 19th century. Foulis mentioned that he discovered the bones of a turtle when describing the island's geology, with later authors claiming that he sent a skull to an unspecified museum. While records of his writing exist, the later claim could not be verified and remains questionable. More scientists arrived on the island around 1869 on the ship Thetis following the murder of a resident. Among these scientist was botanist and poet Robert D. FitzGerald, who according to Clarke (1875) discovered fossil turtles. However this claim too could not be verified by later research, as could the claim that another collection was made by a Mr. Leggatt, despite the fact that these remains were supposedly sent to British paleontologist Richard Owen. However, there are records of FitzGerald writing to Owen regarding later discoveries on Lord Howe Island and notes on turtle remains recorded by zoologist Edward P. Ramsay. Another early record tells of meiolaniid remains being collected by geologist H. Wilkinson during yet another Thetis expedition to the island in 1882. The fossils were originally assigned to two distinct species, M. platyceps and M. minor, tho the latter has since then been sunk into M. platyceps. Not long after Owen named Meiolania, more and more material was published, including fossils much better preserved than the holotype, which have led to revisions regarding Meiolanias classification. In 1887 Thomas Henry Huxley agreed with collectors in that Meiolania was not a lizard but a type of turtle, which he named Ceratochelys sthenurus. In addition to erecting Ceratochelys, Huxley also referred the Queensland skull to this new genus. Meanwhile, upon receiving some additional fossil remains collected by Wilkinson (including a fully preserved skull), Owen came to believe that Meiolania was related to both lizards and turtles and thus placed the animal in a group he called Ceratosauria (a name already occupied by a clade of dinosaurs). When the fossils were examined by George Albert Boulenger, he sided with Huxley, but placed the animal in Pleurodira (side-necked turtles) rather than Cryptodira. This was the first of a long series of differing opinions on the relationship between meiolaniids and modern turtles. Arthur Smith Woodward on the other hand conducted further research on the continental remains and recognized that Owen's composite Megalania further contained the fossils of a marsupial in addition to the monitor lizard and turtle remains. Although he too agreed with Huxley's conclusion that the fossils were those of a turtle, both he and Boulenger pointed out that Meiolania took precedence over Ceratochelys and would thus be the correct name. He also concluded that the Queensland skull was clearly distinct from the material collected on Lord Howe Island and thus coined the name Meiolania oweni for the continental material in 1888. they would eventually found to be distinct enough to retain the original name. Additional finds on Lord Howe Island Another important contributor in the research history of Meiolania was William Nichols, a local who served as a guide and collector for the Australian Museum. According to Gaffney, Nichols' contribution practically doubled the amount of known Meiolania specimens while also finding the first significant shell remains of this genus. After a brief period of little to no new discoveries, Anderson's work with the turtle remains eventually lead to the creation of another species in 1925, when he described the horns and limb bones of a meiolaniid turtle discovered on Walpole Island south of New Caledonia. Originally these bones were discovered by A. C. Mackay, an engineer working for the Australian guano company. These remains were named Meiolania mackayi by Anderson, although later reviews of the material argued that the species was not diagnostic enough to have warranted this distinction. Anderson furthermore was the first to map the distribution of Meiolania across Lord Howe Island, even though the information was largely based on information given to him by Allan Riverstone McCulloch, as Anderson had not visited the island himself. Parallel to Anderson publishing on the Etheridge collection, William Nichol's son-in-law Reginald V. Hines and a schoolteacher named Max Nicholls worked together to continue excavations, uncovering an additional 200 specimens, which they sold to the Australian Museum. Among the most important finds of theirs was a plastron and an articulated hindlimb, which dispelled Anderson's notion that Meiolania was a sea turtle. By the 1940s the locality where both Nichols' and Hine's had recovered their specimens became less relevant, with other areas across the island gaining importance. Among the most important finds from these new localities was a carapace with articulated vertebrae and limb bones, but no skull. The discovery, made at Ned's Beach in 1959, was made rather coincidentally following a joking challenge made by Elizabeth Carrington Pope to Ray Missen, a local meteorologist. While photos were taken during recovery, a collapse of the excavation area nearly destroyed the shell. Eggs were found soon thereafter and during the excavation of a pool the most complete skeleton to date was found. Although uncovered with the use of a jackhammer, the specimen could be pieced together and would eventually serve as the basis for later reconstructions of Meiolania. The best known carapace of Meiolania was discovered in 1977, and much like the remains of Pope and Missen, had been an coincidental find. Alex Ritchie, who worked at the Australian Museum, failed to participate in the recovery of the "swimming pool" skeleton (as it is named by Gaffney). When he was informed of yet another find, he traveled to Lord Howe Island only to conclude that the remains were relatively insignificant. During his stay however he discovered the aforementioned shell and an associated skull on Old Settlement Beach. Work by Gaffney and beyond The next important expedition to Lord Howe Island would be a joint project between the Australian Museum and the American Museum of Natural History in 1980, with the latter returning two years prior for a second dig. These expeditions were the basis for a series of major publications by American researcher Eugene S. Gaffney, now considered to be an expert on meiolaniids. Gaffney's work consisted of complete and detailed descriptions of all known body parts of Meiolania and their significance for the phylogenetic position of the group. Gaffney published three papers on the subject: the first, dealing with the history of Meiolania's discovery and its skull, the second on the vertebrae and tail club, and the final publication covering the shell and limbs while also reviewing Meiolaniidae as a whole. These papers were published in 1983, 1985, and 1996, respectively. In part due to Gaffney's work, meiolaniids had become much better understood by 1992. These advances in our understanding of Meiolania lead Gaffney to re-examine the material of M. oweni, finding that it was sufficiently distinct from all other species to warrant being placed in its own genus, Ninjemys. While this removed one species from the genus, another was added that same year when Dirk Megirian described Meiolania brevicollis based on Miocene remains from the Camfield Beds (Northern Territory) of mainland Australia. Megirian had previously mentioned the Camfield material in a brief report in 1989, but was at that time unable to identify it at a species level. The most recently described species was published in 2010 by White and colleagues, based on limb material from Vanuatu. However, due to the fact that this species is not known from skulls and tail elements, it is uncertain if it actually represents a species of Meiolania and is thus typically referred to as ?Meiolania damelipi both by the original team and subsequent authors. Although the taxonomy of this genus is still not fully clarified, especially with the abundance of isolated remains and species named from poor or possibly non-meiolaniid remains, papers from the 2010s and onward largely focussed on aspects of the animals paleobiology, aided by multiple papers reexamining the South American taxa. 2016 saw an analysis performed on an egg clutch assigned to Meiolania, in 2017 the braincase of Meiolania was studied illuminating some aspects of its lifestyle, and in 2019 Brown and Moll published an extensive review on the dispersal, ecology and lifestyle of the animal. Etymology The meaning of the name Meiolania has been subject to some debate, as Owen didn't offer a detailed etymology in the type description. This has led to two primary hypotheses, both agreeing that the name has the same origin as that of Megalania and that the first element of the name derives from the Ancient Greek "meion" meaning "lesser". The origin of the second part is however less conclusive. Gaffney argues that the suffix derives from the Latin word "lanius", which means "butcher". In this way Meiolania ("lesser butcher") would be complementary to Megalania ("great butcher"). Following Juliana Sterli and colleagues meanwhile the name should translate to "lesser roamer" from the Ancient Greek "ήλaίνω" meaning "to roam about". This argument is supported by the work of Richard Owen himself. Although Owen never gave an etymology for Meiolania, he did provide one for Megalania. Contrary to Gaffney's writing, Owen translates Megalania as "great roamer" rather than "great butcher". ==Species==
Species
M. brevicollis :While most species of Meiolania were recovered from islands, M. brevicollis is the only named species from mainland Australia. Its fossils were discovered at the "Blast Site" near Camfield Station in the Northern Territory. It is thought to be a part of the Bullock Creek Local Fauna, dating to the middle to late Miocene and thus making it the oldest named Meiolania species. M. brevicollis is among the better known Meiolania species and known from partial skulls, neck vertebrae, horn cores, osteoderms, and shell remains. While this is not as much as is known for the type species, it still allows for comparison beyond the size and shape of the horns. :The fossils of ?Meiolania damelipi could represent the youngest record of the genus and meiolaniids as a whole, as they were discovered at the archaeological site of Teouma on Efate, Vanuatu. These bones date to 2,890 to 2,760 BP (ca. 940–810 BC) and were found alongside those of sea turtles. Although the remains of ?M. damelipi are numerous, accounting for 405 bones, their assignment to Meiolania is uncertain as critical components such as tail rings, extensive carapace remains and most importantly skulls and horn cores are absent from the site. Due to this ?M. damelipi (named for Willie Damelip) is only tentatively assigned to Meiolania and could in fact represent a different terrestrial turtle. Other indeterminate Meiolania or meiolaniid fossils have been found across several South Pacific islands including Tiga Island, the Pindai Caves of Grande Terre and Viti Levu (Fiji). While these occurrences are sometimes listed as examples of Meiolania, they are too fragmentary to properly assign to the genus properly and are listed as indeterminate meiolaniids by Gaffney. This highlights one particular issue with the fossil record of Meiolania, the lack of material. Although M. platyceps is known from a large amount of material and M. brevicollis can be morphologically distinguished from it, other members of the genus are mostly known from isolated remains and separated largely on body size, horn thickness and geography. This renders M. platyceps and M. brevicollis the only well understood Meiolania species, with the others being possible synonyms or not even belonging to Meiolania at all. ==Description==
Description
Skull and horns The skull of Meiolania is robust with a rounded snout and a series of horns ornamenting the back. The nasal bones are fused into a single element that protrudes from the skull, though how far is subject to variation. In some specimens it is the front-most part of the skull, while in others the premaxilla extends further. The nares are divided into two by a bony internarial septum, a rarity among turtles. This appears to be a derived trait evolved by the lineage leading up to Meiolania. Basal meiolaniids only feature a single narial opening, while those of Ninjemys are only partially divided. Meiolania platyceps specimens show both states, with some possessing partially and others fully divided nares. This can be attributed either to individual variation or to different growth stages of this part of the skull specifically. It is however not consistent with being overall indicative of age, as the difference in size between these specimens does not line up with the hypothesis. The tympanic cavity of Meiolania is large, comparable to that of modern testudinids. The final segment of the tail is covered by what is generally called a tail club or tail sheath, superficially resembling those seen in certain species of glyptodonts and ankylosaurid dinosaurs. This club consists of four spiked segments similar to the rings and the conical tip of the tail. It is not entirely clear whether or not the club is derived from the tail rings or not. While the overall structure appears similar, with the fused club showing the same spike arrangement, one individual shows sutures that do not fit this interpretation. However it is also possible that said specimen is an outlier that does not represent how the club is typically formed. Unlike the preceding rings, the fused club surrounds the entirety of the vertebrae, lacking the ventral opening seen before. The surface of the club is covered in a multitude of pits and foramina that give it a rugose texture and likely served as pathways for nutrient vessels, indicating that the club itself was covered in a cornified layer of scales. The spikes of the club show a much greater level of variability compared to those on the rings prior. Although still appearing in the form of a dorsolateral and a lateral pair, both of which taper to form backwards-directed points, some Meiolania specimen preserve spikes on their club that are much blunter. The distance between the spikes can vary and even the size progression is subject to intraspecific variation, as typically the spikes of the club peak at the beginning of the club and grow gradually smaller, while in other individuals the spikes reach their greatest size around the second pair. There are signs of abrasion in some fossils, indicating that the bottom layer of scales on the club was gradually damaged by the animal dragging its tail over the ground. The tip of the club consists of nearly solid bone, with the final vertebra being barely separated from the surrounding ring. The tip of the club, like the spikes, may be pointed or blunt depending on the specimen. ==Phylogeny==
Phylogeny
Unlike the relationship between meiolaniids and other turtles, the internal structure of Meiolaniidae is well understood with research consistently recovering the same results. Within its family, Meiolania is placed as one of the most derived members, displaying several features that are observed to have changed between the earliest meiolaniids and Meiolania itself. Within the species Meiolania things are less certain, primarily due to how fragmentary or even undiagnostic some species are. It is hypothetically possible to find clades within the genus based on the width of the B horns, however as Gaffney notes this is not a consistent feature and varies greatly once one is met with a greater sample size. ==Paleobiogeography==
Paleobiogeography
While the geographic range of early meiolaniids and the continental Meiolania brevicollis are easily explained through the breakup of Gondwana, other means of dispersal must have been necessary to account for the many remains found on offshore islands. A commonly proposed but somewhat controversial hypothesis for the appearance of Meiolania is direct dispersal across water, which may range from drifting, floating, walking, and wading to active swimming. While some authors simply suggest that Meiolania was a terrestrial animal capable of swimming, others suggest an aquatic lifestyle altogether. The final hypotheses for the discovery of meiolaniids on remote islands depends more on geological events and terrestrial movement rather than trans-oceanic travel. One explanation could be found in what is termed the "escalator hopscotch" model. According to this model, an island chain may undergo a process that would see land emerge on one and of the chain and submerged on the other. This may go on in a continuous fashion and thus allow an animal, such as Meiolania, to either travel over directly connected islands or swim through narrow waterways. This means that even if one particular island has only emerged recently, the fauna on it could have arrived from a nearby island that is no longer above sealevel. This scenario can be applied to Meiolania platyceps on Lord Howe Island for instance, as the island is simply the latest in a series of volcanic islands formed by the Lord Howe Rise. Brown and Moll meanwhile favor the hypothesis that Zealandia could have played an important rolle in the dispersal of Meiolania. According to them, many of the islands Meiolania was native to are in fact parts of a now largely submerged Zealandia and could indicate that these turtles were more widespread in the past, only to be "stranded" on the remote islands after the continent was flooded. ==Paleobiology==
Paleobiology
Lifestyle The idea that Meiolania was a marine animal has been suggested a multitude of times since its initial discovery. Allan Riverstone McCulloch for instance believed that the fossils on Lord Howe Island were preserved when turtles came ashore to lay their eggs, only to die in the process. Anderson meanwhile, who described a series of limb elements of what he considered to be two different species, likened Meiolania to marsh and river turtles, noting that its limbs were far less specialised than those of true sea turtles. He proposed that Meiolania was more semi-aquatic, inhabiting the shore and estuaries while still being capable of traveling the ocean to disperse to other islands. Various aspects of its general morphology also draw closer comparison to terrestrial tortoises than aquatic ones, such as the robustness of the limbs, the rounded head of the femur and the shape of the shoulder girdle. ==Extinction==
Extinction
Due to the great range of Meiolania, which covered many ecosystems entirely independent from each other, the genus' extinction is thought to have been a multifaceted process caused by various factors not directly tied to one another. Another, even younger, instance of a meiolaniid surviving into human times stems from New Caledonia. The remains from Pindai Cave have been dated to 1720 ± 70 years BP ((160–300 AD) via uncalibrated radiocarbon dating and 1820–1419 years BP (130–531 AD) through calibrated 14C dating. While it is unclear whether or not these remains belong to Meiolania itself like those from nearby Walpole Island, it is at least confirmed to actually represent a meiolaniid, unlike the uncertainty regarding ?M. damelipi. ==See also==
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