Meiolania
Meiolania Temporal range:
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Cast of a Meiolania platyceps skeleton, American Museum of Natural History | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Clade: | Pantestudines |
Clade: | Testudinata |
Family: | †Meiolaniidae |
Genus: | †Meiolania Owen, 1886 |
Species | |
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Synonyms | |
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Meiolania is an
The best known species is M. platyceps, known from hundreds of specimens collected in Pleistocene strata of Lord Howe Island. The oldest known species is M. brevicollis from the Miocene of mainland Australia. Other species include M. mackayi from Pleistocene New Caledonia, which may be synonymous with M. platyceps, ? M. damelipi from Holocene Vanuatu, which may represent a non-meiolaniid turtle, and the Wyandotte species, an unnamed form from Pleistocene Australia tentatively identified as M. cf. platyceps by meiolaniid researcher Eugene S. Gaffney. Additional fossil remains indicate the presence of Meiolania or a close relative in multiple localities across Australia, New Caledonia and Fiji.
Meiolania was a well-armored animal with a somewhat raised
Neither the dispersal nor the extinction of Meiolania are fully understood. Several hypotheses have been proposed ranging from it spreading across the now submerged continent of Zealandia to it swimming between islands (the latter of which is now considered unlikely based on its heavy build and lack of aquatic adaptations). The extinction of this turtle was most likely a multi-facetted process with ties to climate change, reduction of its native territory by rising sea levels, predation from invasive livestock and possibly hunting by humans. However, some of the youngest records are uncertain, with the roughly 3.000 year old ?M. damelipi possibly being another type of turtle and the even younger, ca. 2.000-1.500 year old, Pindai Cave meiolaniid being indeterminate at a genus level.
History and naming
Early research
Perhaps the first recorded discovery of meiolaniid remains stems from John Foulis, a doctor who lived on
In 1884 turtle fossils once again found their way into the possession of FitzGerald, who proceeded to send the remains to Owen in
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).[6] 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.[7][5][3]
Additional material was then described in 1889 from
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.[1]
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.[10][4] In addition to describing a new species, Anderson further supervised the creation of a skull reconstruction of Meiolania and described a great many remains collected towards the end of the 19th century on Lord Howe Island. With this Anderson finished the project started by Etheridge years prior.[3] 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.[1]
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.[1]
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.[1]
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,[1] the second on the vertebrae and tail club,[11] and the final publication covering the shell and limbs while also reviewing Meiolaniidae as a whole.[4] 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.[12][5] 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.[4] 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.[10]
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.[13]
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,[14] in 2017 the braincase of Meiolania was studied illuminating some aspects of its lifestyle,[15] and in 2019 Brown and Moll published an extensive review on the dispersal, ecology and lifestyle of the animal.[16]
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.[2] 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").[4] Juliana Sterli and colleagues meanwhile translate the name 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
- M. brevicollis[10]
- 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.[4] The species name brevicollis was chosen in reference to the neck, which is shorter than that of M. platyceps.[10]
- The fossils of ?Meiolania damelipi could represent the youngest record of the genus and meiolaniids as a whole, as they were discovered at the 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.[13] Later excavations have revealed additional bones, but still failed to recover horn cores. It has also been noted that ?M. damelipi bears resemblance to fossil turtles from Fiji.[17][18][19]
- M. mackayi[3]
- Known from the Pleistocene of Walpole Island, M. mackayi is known primarily from isolated horn core remains as well as a few limb bones. This species generally resembles M. platyceps, but was described as having narrower horns and more gracile limbs. However, according to Gaffney the fossil remains are not adequate enough to support a new species. While Gaffney concedes that it could represent a distinct biological species due to the isolation of Walpole Island, it does not show many physical differences from the better known species. This is followed by Sterli, who reasons that the two populations could have become genetically distinct due to being unable to maintain gene flow over such a large distance.[9] However as the material had already been named, Gaffney retained the species in his 1996 review as the name has some value in making discussion easier.[4] It was named after A. C. Mackay, an engineer who discovered the first fossils.[3]
- M. platyceps[2]
- The type species of the genus, M. platyceps is also the best known of the recognized species and is represented by several hundred individual bones as well as a few articulated skeletons. While the extensive number of fossil remains establishes M. platyceps as the de facto species used in comparison with other turtle groups, it also serves to highlight the shortcomings of the less complete species, as M. platyceps specimens show a great range of intraspecific variation. Meiolania platyceps was endemic to Lord Howe Island, the remnant of a former volcano located between Australia and New Zealand and lived during the Pleistocene.[4] Meiolania platyceps also includes specimens previously named Meiolania minor by Owen.[2]
- Wyandotte Species[12]
- A large bodied Meiolania from Wyandotte Creek on Australia's mainland. The bones of the Wyandotte species were recovered from the Late Pleistocene (45,000 and 200,000 BP) of northern Queensland, with a potential second locality from Darling Downs. As the material of this "species" only consists of isolated horn cores and tail vertebrae, it has not been named and simply referred to by the name of the locality it was found at. Gaffney cautions against establishing species based on variable features such as horn cores and tentatively assigns the Wyandotte remains to Meiolania cf. platyceps. Gaffney does however still note the great size of the animal, its unique geography compared to other Pleistocene Meiolania species and the fact that the horns do not fully match those of the other established species.[4][20][12]
Other indeterminate Meiolania or meiolaniid fossils have been found across several
Description
Skull and horns
The skull of Meiolania is robust with a rounded snout and a series of horns ornamenting the back. The
Like other meiolaniids, Meiolania is easily identifyable by the size and shape of the various scale areas. In the absence of many of the actual bone
The scale areas of Meiolania are described as consistently showing at least slightly raised centers, so while they may not all form horns they are thicker in the middle than towards the edges. The X scale, which is a singular scale in the center of the skull roof, is small and rhomboid in shape. Furthermore, it is concave, meaning it forms somewhat of an indentation in the skull in profile view. While this scale projects in-between the D and G scales, it does not prevent either of those pairs from contacting each other along the midline. Although the D scales have been described as slightly convex, said convexity is only poorly developed compared to other meiolaniids and thus appears much lower, setting Meiolania apart from Ninjemys and Niolamia. The G scales are much smaller and almost fully separated by the X scale. Like the D scales, they are not especially convex and appear flat. The Y and Z scales, covering the front-most areas of the skull from between the eyes to the tip of the snout, are both large and unpaired. Scale Z is the more anterior of the two, covering the very tip of Meiolania's snout and the nasal area. Although the margins between the Z and Y scale are raised, towards the bottom of the jaw where the Z scale connects to the F scales this ridge becomes a trough. Scale Y meanwhile covers much of the area between the two eyesockets and is larger than scale Z. This scale features a very prominent convexity, meaning it bulges out giving it a somewhat domed appearance. Although the Y scale is also slightly raised in Ninjemys, it is not as extreme as in Meiolania.[4][1]
The F scales cover the entire area between the eyesockets and the dorsal Y and Z scutes, which effectively amounts to half of the area surrounding each eye. They meet the H scales towards the back of the skull. The H scales are somewhat shaped like a
Postcrania
Limbs
The shoulder girdle is typically chelonian, showing the three prongs formed by the scapula and coracoid also seen in other turtles. As with most of Meiolania's anatomy, the shoulder girdle is more robust than in most turtles, bearing similarity to terrestrial tortoises. The dorsal process of the shoulder blade is nearly cylindrical, ending in a rounded surface that articulates with the shell. The second process of the shoulder blade, known as the acromial process, diverges from the dorsal process at a 120° angle. The angle between these two processes has been used as an indicator for shell depth, as it joins at a right angle of 90° in the shallow-shelled aquatic turtles and at more obtuse angles in high-shelled turtles like tortoises and snapping turtles. This is confirmed in Meiolania when examining the shell remains themselves. The final of the three processes of the shoulder blade is formed by the coracoid, which is a short and fan-shaped element like in tortoises.[4]
There is no complete hip for Meiolania, but numerous partial remains have been found. The
The front limbs of Meiolania were short and stout, especially in M. platyceps, resembling those of terrestrial tortoises and thus disspelling early notions researchers had about Meiolania being marine. Humerus bones are well sampled and consequently, a lot of variation is present. For instance, some are noted by Gaffney for being unusually rugose in their surface texture. The carpal bones consist of seven elements, three proximal bones articulating with the radius and ulna while the remaining four connect to the fingers. The presence of three proximal carpals stands out, as most other turtles have four proximal carpals instead. While at least some modern species also possess three, this is due to two of them having been fused, creating a single elongated bone. This does not appear to be the case in Meiolania and it is instead hypothesized that the missing bone was either simply absent or consisted purely of cartilage, preventing it from fossilizing along the others. Something similar could be the case with the distal carpal bones, which like the proximal ones lack one bone compared to other turtles. Five fingers were present on each of Meiolanias forelimbs. The first finger was short and wide, followed by three fingers of roughly equal length and a fifth, shortened finger. Each finger is tipped by blunt and flat unguals resembling those of gopher tortoises, rather than the narrow and curved claws seen in terrapins and snapping turtles.[4] The limbs of ?Meiolania damelipi meanwhile were described as being relatively more gracile.[13]
The
Neck
The neck vertebrae are known from two species: M. platyceps and M. brevicollis. The former had vertebrae that were longer, wider and lower while those of the later were shorter, narrower and taller. The
Tail and tail club
As no fully articulated tails are available, it is not known how many vertebrae formed the caudal series. Gaffney suggests that a minimum of 10 vertebrae formed the tail based on comparison with modern turtles. It is possible that there were more, but unlikely for there to have been fewer. Following this interpretation, the tail of Meiolania would have been proportionally long, similar to those of modern snapping turtles. The tail of Meiolania was protected by a series of armored rings. These rings do not fully enclose the tail around its circumference, as the bottom of the segment is open and the ring thus incomplete. This is different from the rings in more basal species, in which the rings are closed. Based on specimen AMF:9051 these rings articulated with one another and correspond directly with the vertebrae, meaning each ring surrounds a single tail vertebra. It is unclear exactly how much of the tail was covered by rings. The best preserved fossils primarily show those towards the end of the tail, however, Gaffney proposes that the entire length would have been covered. Evidence to support Gaffney's claim can be found in some isolated material initially described as a "sternal arch" by Owen. Based on this fossil the rings begin as much wider elements, corresponding with a broader tail closer to the torso. These earlier rings are comparably thin and do not immediately articulate with one another, meaning they don't overlap as the posterior ones do. Along the length of the tail, two pairs or ridges situated on the surface of the rings gradually grow and form two distinct pairs of thorn-like spikes towards the tails end. The larger pair is placed atop the rings and curves up and backwards, while the second pair projects from the side of the rings and is notably smaller.[11]
The final segment of the tail is covered by what is generally called a
Shell
The shell of Meiolania is roughly ovoid with parallel edges and a protruding front. It lacks the cephalic notch, an indentation in the front of the shell, as well as the caudal notch towards the back of it. The very back of the carapace is serrated, with the scutes forming a spiked edge. There are however questions regarding the precise shape of the carapace that aren't fully resolved. The most complete specimens all preserve it as flattened, but also clearly suffered from distortion and collapse of the shell during the fossilisation process, thus not reflecting its form in life. Analysis of individual shell elements all indicate at least some degree of vaulting. This indicates that the overall shape of the carapace is raised or arched, however, probably not nearly as pronounced as the vaulting seen in modern giant tortoises. Instead, the shell of Meiolania is thought to have resembled the shape seen in species of the gopher tortoise.[1]
Size estimates
Size estimates differ between all recognized species. M. mackayi was among the smaller species, 30% smaller than M. platyceps, which in turn was 10 to 20%[10][4] smaller than M. brevicollis and only half the size of the Wyandotte species.[4] Put into numbers, M. mackayi is considered to have reached a carapace length of approximately 0.7 m (2 ft 4 in) and M. platyceps was estimated to reach a carapace length of 1 m (3 ft 3 in). Rhodin notes that the largest complete M. platyceps carapace measures 63.5 cm (25.0 in), and that the size of larger specimens was estimated based on the proportions of this individual.[18] Another method used to determine the size of Meiolania was to compare the size of fossil eggs with those of modern tortoises. Based on this method, Lawver and Jackson estimated that one individual M. platyceps responsible for a clutch of 10 eggs must have had a carapace length of around 75 cm (30 in).[14] Furthermore, some sources claim that Meiolania platyceps could reach lengths of more than 3 m (9.8 ft) including the tail, neck and head.[16] The Wyandotte species stands out as the largest member of Meiolania, with the horn cores indicating an animal similar in size to Ninjemys[12] and a carapace length of perhaps up to 2 m (6 ft 7 in). ?M. damelipi was described as being of a similar size to M. platyceps, with Rhodin and colleagues estimating a length of 1.35 m (4 ft 5 in) based on limb material.[17][18]
Species | Carapace length |
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M. brevicollis | 10-20% larger than M. platyceps[10][4] |
?M. damelipi | 1.35 m (4.4 ft)[18] |
M. mackayi | 0.7 m (2.3 ft)[18] |
M. platyceps | 0.63–1 m (2.1–3.3 ft)[18] |
Wyandotte species | 2 m (6.6 ft)[18] |
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.[12] The second accessory chewing surface, divided nares and small X scale first appeared at the beginning of the Australasian group that unites all meiolaniids other than Niolamia. Furthermore, Ninjemys is excluded from the clade formed by Warkalania and Meiolania in part based on the anatomy of the D scales, which is high in the former and low in the latter. Finally, the recovered cow-like horns and absence of a continuous shelf of scales at the back of the skull separates Meiolania from its closest relative, Warkalania. Throughout this family tree, one can also observe a gradual decrease in the size of the A scales, which begin as a large shield-like structure in basal taxa like Niolamia and Ninjemys and are comparably reduced in Meiolania. The B horns change orientation, protruding sideways in early forms and curving back in later species, however here Warkalania represents an outlier with its highly reduced horns.[4][5] One wildcard is represented through Gaffneylania, the most recently described meiolaniid, as it was recovered in several different positions within the family. However this is largely due to its very fragmentary nature that leaves several important traits ambiguous.[21]
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.[4]
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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.[16] Mittermeier even goes as far as to suggest that meiolaniids had marine ancestors, a hypothesis not favored by modern phylogenetic analysis.
Brown and Moll (2019) deem active travel through saltwater unlikely and even flat out impossible. According to them the head size, large horns, fused bones, heavy ossification and inability to retract the head, combined with the animal's neck flexibility being primarily adapted for downward movement while grazing, would have caused difficulties with keeping the head above water while swimming or floating. Their limbs are proportionally short and similar to those of tortoises, differing clearly from the flippers of sea turtles and the limbs of other aquatic turtles, making them inefficient tools for active swimming. Adding to that is the likelihood that they were covered in
While they may not have been actively swimming to settle new islands, another possibility is dispersal through
Yet another hypothesis stems from Bauer and Vindum (1990), who suggest that Meiolania could have arrived on New Caledonia not through natural dispersal but because they were introduced there by humans. Although there are known examples of living giant tortoises being transported on ships as a source of food, this hypothesis is nonetheless considered unlikely by Brown and Moll. They point out multiple problems with the idea that render human introduction an impracticle and unlikely scenario. The transport of mature Meiolania would have come with several issues, in particular related to the size and armored, possibly very defensive nature of these animals. Even if humans had been able to subdue and transport large adults over great distances, they would have had to introduce a great number of them in order to sustain the population given the slow reproduction cycles of tortoises. Finally, studies have shown that adult tortoises introduced to new areas are very likely to disperse soon after release if not contained, an inconvenience if the turtle was meant to serve as a foodsource. The introduction of juveniles would be easier logistically due to their smaller size and the increased likelihood of them staying in the area they were released in. However, they too make for a poorly sustainable source of meat due to the long time tortoises take to grow and reproduce, again causing issues with establishing a stable population. Brown and Moll further point out that there is no evidence that the Lapita kept or even domesticated Meiolania.[16]
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.[4] 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.[16]
Paleobiology
Lifestyle
The idea that Meiolania was a marine animal has been suggested a multitude of times since its initial discovery.
Among the most recent publications suggesting a more aquatic way of life was Lichtig and Lucas (2018). Their analysis primarily focused on shell dimension ratios and limb anatomy in comparison to modern turtle species, leading to them proposing that Meiolania was a bottom walker they liken to modern members of the Chelydridae, the snapping turtles. However, this hypothesis was rejected by Brown and Moll the following year. Besides the questionable nature of their ratio-based approach, the two authors point out that Lichtig and Lucas based their conclusion on a single juvenile specimen which was a composite reconstruction, thus not only providing an extremely poor sample size but also not reflecting the real proportions of the animal, much less those of an adult. Yet another problem pointed out by Brown and Moll is that the aquatic nature proposed in the Lichtig and Lucas study only results from one of the two calculations offered by them.[16]
Most other authors, historical as well as contemporary, support the idea that Meiolania was terrestrial. One study with major implications for this hypothesis was published by Paulina-Carabajal et al. in 2017. In this study, the
Diet
Multiple aspects of Meiolania's anatomy have been used to infer its diet. The flexibility of the neck being largely focused on side to side movement and restricted by the projection of the carapace as well as the weight of the horns are thought to indicate that Meiolania was a terrestrial
Reproduction
Although nothing concrete is known about the mating behavior of Meiolania, a widespread hypothesis suggests that the highly ornamented skull, armored limbs and tail club could have served a function in intraspecific combat between rival males during the mating season. Combat may have been instigated through chemical cues produced by one of the many scent glands found in modern turtles (musk glands, cloacal secretions and mental glands). While such glands are not preserved in fossils, the enlarged nasal cavity and inferred heightened sense of smell support this interpretation. Modern tortoises engage with rivals primarily through maneuvers performed with the shell, including knocking, ramming, twisting and others. Combat between Meiolania specimens could further involve the use of armored limbs, the spiked tails covered in bony rings and the large horns situated atop the animal's head. This may also explain the great sideways mobility that has been inferred for Meiolania's neck.[16][15]
Meiolania platyceps is thought to have at least occasionally traversed the beaches of Lord Howe Island, at the very least while laying eggs.
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.[13]
On the islands of the South Pacific the rising sea levels following the
However, there are potential exceptions to this. Among the most recent records of Meiolania may be that of ?M. damelipi from Vanuatu (assuming the remains are actually those of a meiolaniid). These remains were initially found in archaeological layers above those of a human graveyard, with the remains dating to roughly 2,800 BP. Later studies identified similar sites across Vanuatu and Fiji, greatly extending the area across which humans and megafaunal turtles came in contact with each other. White and colleagues propose that the turtles at the Vanuatu site may have been butchered for their meat based on the fact that only limb bones were present in abundance, i.e. parts of the turtle that would have been much fleshier than the diagnostic skulls and tails. The bones recovered at the site show clear signs of being cut up and consumed, showing marks left by cutting tools, burns and fractures in addition to all bones being found in association with human settlements. Although hunting of turtles by the
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
See also
References
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- ^ .
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- ^ a b c d e Gaffney, E. S. (1992). "Ninjemys, a new name for "Meiolania" oweni (Woodward), a Horned Turtle from the Pleistocene of Queensland" (PDF). American Museum Novitates (3049): 1–10.
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- ^ a b c d e f Gaffney, E.S.; McNamara, G. (1990). "A meiolaniid turtle from the Pleistocene of Northern Queensland". Memoirs of the Queensland Museum. 28 (107–113).
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- ^ (PDF) from the original on 21 September 2022.
- ^ ISBN 9780128175552.
- ^ McNamara, G.C. (1990). "The Wyandotte Local Fauna: A New, Dated, Pleistocene Vertebrate Fauna from Northern Queensland". Memoirs of the Queensland Museum. 28: 285–297.
- hdl:11336/41594.