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78-474: Meiolaniidae is an extinct family of large, probably herbivorous stem-group turtles with heavily armored heads and clubbed tails known from South America and Australasia . Though once believed to be cryptodires , they are not closely related to any living species of turtle, and lie outside crown group Testudines , having diverged from them around the Middle Jurassic . They are best known from

156-464: A carapace length of 1 m (3 ft 3 in) and Niolamia was estimated at 1.2 m (3 ft 11 in). The largest sizes were seemingly reached by Ninjemys and the Wyandotte species. Both were estimated to have reached a similar weight and the latter was estimated to have reached a carapace length of up to 2 m (6 ft 7 in). Notably, these length estimates are restricted to

234-483: A new genus with reduced horns. Only two new taxa have been named since this boom in the 1990s, with ? Meiolania damelipi representing an uncertain member of this group from Holocene of Vanuatu and Fiji and Gaffneylania being a second genus from the Eocene of Argentina in addition to Niolamia . Meiolania As meiolaniid fossils are often found in the form of broken horn cores and tail rings, much of

312-407: A phylogenetic tree for the individual species of Meiolania is theoretically possible, however as discussed by Gaffney, the results of doing so are highly questionable. Only two species would be complete enough to provide valuable characters, as M. mackayi is likely a synonym of M. platyceps and the wyandotte species is only represented through horn cores. This renders the morphology of the B horns

390-421: A short communication in which he names Niolamia argentina , a large meiolaniid turtle he claimed was found by his brother Carlos . Simultaneously, Woodward received material from collector Santiago Roth , who had discovered a strikingly similar animal. Roth's find was first figured in a communication by Moreno and was later described in greater detail by Woodward. Having heard of Ameghino's Niolamia argentina ,

468-432: A stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all

546-469: A system already used in a similar form during early research and later refined by Gaffney. Some consistent features of these scales include the presence of paired G and D scales covering the roof of the skull, a singular X scale sitting at the center of these scales which varies in size between basal and derived genera and unpaired Y and Z scales that sit between the eyes and over the nose. The most prominent scale areas are those designated A to C in order from

624-461: A tail club towards the tip. While their lifestyle was long debated, current research indicates that they were terrestrial herbivores with a keen sense of smell that may have used their heavily armored bodies in intraspecific combat , perhaps during mating season . The research history of meiolaniids is long and at times complicated, with especially the early years suffering from poor records, incorrect identifications and loss of information. Some of

702-750: A tail ring, dates to the Late Eocene and has been discovered in the Rundle Formation of Queensland. Remains found in Early Miocene Canadian Lead near Gulgong (New South Wales) seem to belong to an intermediate taxon, combining the flattened horns of taxa like Niolamia and Warkalania with the recurved horns of Meiolania . Other continental remains were found in the Late Oligocene Etadunna Formation and Namba Formations (South Australia),

780-462: A turtle, he proposed it was a member of Pleurodira, the side-necked turtles, which today include Southern Hemisphere groups like chelids , podocnemidids and pelomedusids . Boulenger would find support from Richard Lydekker and meiolaniids were generally viewed as pleurodires for the following decades. Anderson and Simpson both suggested that meiolaniids were part of neither group, instead declaring them descendants of early turtles and placing them in

858-566: Is clearly differentiated through the horn core anatomy. Indeterminate remains from islands have been discovered in the Pleistocene to Holocene Pindai Caves on New Caledonia , Fiji and Tiga Island . Furthermore, Worthy et al. (2011) reported on what may be the remains of a meiolaniid from the Miocene St Bathans Fauna of New Zealand . However, as the remains do not represent the characteristic horns or tail rings,

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936-458: Is consistently found to be the basalmost meiolaniid, sitting at the base of the tree as a sister to all Australasian forms. This matches its geographic range and age, which clearly separates it from younger meiolaniids. Some of the seemingly ancestral scale conditions of Niolamia includes the enormous A scale area and the more laterally directed B horns, both traits shared with the basalmost Australian form Ninjemys . The basal condition of Niolamia

1014-401: Is further supported by comparing the basicranium to other turtle groups, as the intrapterygoid appears more "primitive" compared to that of Meiolania and compares favorably with sinemydids . The absence of an accessory grinding surface in the jaws also identifies it as a sister taxon to the other meiolaniids. Although Gaffneylania likely lived alongside Niolamia , the fragmentary nature of

1092-423: Is given the designation "crown-", to separate it from the group as commonly defined. Both birds and mammals are traditionally defined by their traits, and contain fossil members that lived before the last common ancestors of the living groups or, like the mammal Haldanodon , were not descended from that ancestor although they lived later. Crown-Aves and Crown-Mammalia therefore differ slightly in content from

1170-632: Is no consensus phylogeny. Stem arthropods constitute a group that has seen attention in connection with the Burgess Shale fauna. Several of the finds , including the enigmatic Opabinia and Anomalocaris have some, though not all, features associated with arthropods , and are thus considered stem arthropods. The sorting of the Burgess Shale fauna into various stem groups finally enabled phylogenetic sorting of this enigmatic assemblage and also allowed for identifying velvet worms as

1248-434: Is not necessary for a species to have living descendants in order for it to be included in the crown group. Extinct side branches on the family tree that are descended from the most recent common ancestor of living members will still be part of a crown group. For example, if we consider the crown-birds (i.e. all extant birds and the rest of the family tree back to their most recent common ancestor), extinct side branches like

1326-558: Is so reduced its even described as being vestigial. The B horns on the other hand are typically well developed and conical rather than flattened. Typically the horns of Meiolania are recurved, resembling the horns of bovines like cows. This is most pronounced in M. brevicollis and the Wyandotte species, which have the proportionally largest horns. However, the large sample size of Meiolania platyceps specimens also highlights how variable these turtles can be, as some individuals show clearly defined B horns while others have them no larger than

1404-896: Is speculated that meiolaniids were also present on the latter, although no fossils of them have yet been found there. Furthermore, meiolaniids may have been present on New Zealand based on the discovery of turtle remains as part of the St Bathans Fauna . Meiolaniids were large animals, with the bigger species reaching total lengths of perhaps up to 2–3 m (6.6–9.8 ft). Meiolaniid remains can easily be identified by their skulls, which are covered in distinctive scale patterns and formed elaborate head crests and horns that vary greatly between genera. While some such as Niolamia had massive frills and sideways facing, flattened horns, others like Meiolania had cow-like, recurved horns. They also had long tails that were covered in spiked rings of bones that, at least in some genera, transitioned into

1482-461: Is the crown group and all organisms more closely related to it than to any other extant organisms. In a tree analogy, it is the crown group and all branches back to (but not including) the split with the closest branch to have living members. The Pan-Aves thus contain the living birds and all (fossil) organisms more closely related to birds than to crocodilians (their closest living relatives). The phylogenetic lineage leading back from Neornithes to

1560-458: Is thought by some to make the Cambrian explosion easier to understand without invoking unusual evolutionary mechanisms; however, application of the stem group concept does nothing to ameliorate the difficulties that phylogenetic telescoping poses to evolutionary theorists attempting to understand both macroevolutionary change and the abrupt character of the Cambrian explosion . Overemphasis on

1638-493: The crown group . Their analysis recovers meiolaniids as deeply nested in a group of primarily Gondwanan turtles they named Meiolaniformes, which contradictory to the previously held opinion indidcates that meiolaniids sit on a branch of turtles that lies outside of the Pleurodira Cryptodira clade. Pleurodira Cryptodira Chubutemys copelloi Mongolochelys efremovi Stem group The concept

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1716-405: The dinosaurs and the pterosaurs . The last common ancestor of birds and crocodilians—the first crown group archosaur—was neither bird nor crocodilian and possessed none of the features unique to either. As the bird stem group evolved, distinctive bird features such as feathers and hollow bones appeared. Finally, at the base of the crown group, all traits common to extant birds were present. Under

1794-531: The dodo or great auk are still descended from the most recent common ancestor of all living birds , so fall within the bird crown group. One very simplified cladogram for birds is shown below: † Archaeopteryx other extinct groups Neornithes (modern birds, some extinct like the dodo) In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of

1872-466: The last common ancestor of the crown group and their closest living relatives. It follows from the definition that all members of a stem group are extinct. The "stem group" is the most used and most important of the concepts linked to crown groups, as it offers a means to reify and name paraphyletic assemblages of fossils that otherwise do not fit into systematics based on living organisms. While often attributed to Jefferies (1979), Willmann (2003) traced

1950-426: The lungfish , our nearest relatives among the fishes. In addition to a series of lobe-finned fishes , they also include some of the early labyrinthodonts . Exactly what labyrinthodonts are in the stem group tetrapods rather than the corresponding crown group is uncertain, as the phylogeny of early tetrapods is not well understood. This example shows that crown and stem group definitions are of limited value when there

2028-604: The wastebasket taxon Amphichelydia. During the 1970s Amphichelydia fell out of use, with groups previously included in it being split among pleurodires and cryptodires. Gaffney at the time argued that meiolaniids were not just cryptodires, but eucryptodires, placing them as a sister group to today's snapping turtles, pond turtles and tortoises , sea turtles as well as pig-nosed and softshell turtles . Fossil discoveries made since them have drastically changed this however. Several genera of Mesozoic turtles have been found to share similarities to meiolaniids, giving crucial insight into

2106-488: The C horns are typically reduced and knob-like. Niolamia possesses the most elaborate A horn, which forms a structure somewhat resembling the frill of a ceratopsian , while the flattened B horns extend to the sides and back. Little is known about the horns of Gaffneylania meanwhile, however the singular known B horn indicates that it may have looked similar to Niolamia , if with more rounded tips. While Ninjemys lived long after these Eocene forms, its horn structure mirrors

2184-498: The C horns. The reason for this is currently unknown, but sexual dimorphism is considered to be unlikely given how these horn morphs are distributed across specimen. The most reduced horns can be observed in Warkalania . Although all three horn types are still present and distinct, they are much more reduced and form neither a large frill nor pronounced B horns, instead only appearing as a relatively subtle ridge extending from behind

2262-527: The Crocodilia branch. Basal branch names such as Avemetatarsalia are usually more obscure. However, not so advantageous are the facts that "Pan-Aves" and "Aves" are not the same group, the circumscription of the concept of "Pan-Aves" (synonymous with Avemetatarsalia) is only evident by examination of the above tree, and calling both groups "birds" is ambiguous. Stem mammals are those in the lineage leading to living mammals, together with side branches, from

2340-528: The Early Cretaceous-Paleocene of South America and Australia. Meiolaniidae includes a total of five different genera, with Niolamia and Gaffneylania native to Eocene Patagonia and the remaining taxa, Ninjemys , Warkalania and Meiolania being endemic to Australasia . The group is believed to have evolved on the continent of Gondwana prior to its split into South America, Australia and Antarctica . For this reason it

2418-729: The Early Miocene Carl Creek Limestone of the Riversleigh (Queensland), the Middle Miocene Wipajiri Formation (South Australia) and the Pliocene Chinchilla Sands (Queensland). Some of these may have beend alongside named genera, indicating that two or more meiolaniids could be found in the same environment. The indeterminate Riversleigh meiolaniid for instance likely coexisted with Warkalania , which

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2496-504: The Roth skull to his brother. No new species were named between 1938 and the 1990s. Instead, the vast quantity of fossil material collected on Lord Howe Island led to a series of major publications penned by Eugene S. Gaffney, now renowned for his work on this group. Split across three papers published in 1983, 1985 and 1996, Gaffney described in great detail the skull, vertebrae and finally the shell and limbs of Meiolania platyceps , providing

2574-553: The South American genera and likely indicates that this is the basal condition. In Ninjemys too the A horn forms an enlarged frill, even if less pronounced than in Niolamia , and the B horns face straight to the side. Meiolania as the most recent genus represents an extreme in regards to this gradual reduction of the A horn, with the structure only forming a small shelf at the back of the skull. In M. brevicollis this area

2652-456: The affinities of this form may change. The most defining feature of meiolaniids is the presence of clearly defined scale areas covering the skull . In meiolaniids, the individual plates that form the skull are highly ankylosed, meaning they are fused with each other to a degree that typically makes it impossible to determine where one element ends and the other begins. Despite the absence of such sutures however, researchers can readily distinguish

2730-484: The back of the carapace had a serrated edge. Osteoderms that covered the limbs have been recovered from both Meiolania and Gaffneylania and the overall morphology of the legs, which is robust with blunt toes, also supports terrestrial locomotion. Meiolaniids were large and robust animals. Even the smaller species, namely Meiolania mackayi , have been estimated to have reached a carapace length of 0.7 m (2 ft 4 in). Meiolania platyceps could have reached

2808-465: The back-most area to the front-most pair. These scale areas, commonly referred to as horns or horn cores due to their size and shape, are very pronounced and highly distinct in the individual genera and even species. Generally speaking, the A horn is a singular element located at the back of the skull that ranges from forming a large, frill-like structure to an almost vestigial shelf. The B scales are paired and appear more horn-like in their morphology, while

2886-657: The basalmost Meiolania species. The Wyandotte species was not used in this analysis due to it being too fragmentary. Niolamia Ninjemys Warkalania Meiolania platyceps Meiolania mackayi Wyandotte species Meiolania brevicollis Niolamia Ninjemys Warkalania Meiolania brevicollis Meiolania mackayi Meiolania platyceps While their internal relationships are relatively well understood, their relation to other turtles has long remained elusive. Throughout their history, they've been variable considered pleurodires , cryptodires or an entirely separate, independent group. Many of

2964-480: The bony shell and do not factor in the combined length of the head, neck and long tail. This may indicate that meiolaniids could have reached lengths of up to 3 m (9.8 ft). Phylogenetic analysis consistently recovers Meiolaniidae as a monophyletic group with well resolved internal relationships. Among the most important features in this are the different scale areas, which provide the majority of characters used in phylogenetic analysis of this group. Niolamia

3042-640: The broad head and the partially separated internal nares. However, it is excluded from the Warkalania and Meiolania clade due to the size of the A horns and the shape of the D scales. Pictured below is the phylogenetic tree recovered in Sterli, de la Fuente and Krause in 2015. Other than the wildcard Gaffneylania , the phylogenetic tree matches with prior work by Gaffney. Niolamia argentina Gaffneylania auricularis Ninjemys oweni Gaffneylania auricularis Warkalania carinaminor Gaffneylania auricularis Meiolania platyceps Creating

3120-540: The chimeric hypodigm of Megalania into monitor lizard, marsupial and turtle remains, with the name being constrained to the lizard. While this marked the end of Meiolania as a lizard, Woodward agreed with Owen in that the skull from the mainland clearly belonged to an animal related to Meiolania . Woodward placed it in the same genus, naming it Meiolania oweni in Owen's honour. Shortly afterwards, M. platyceps and M. minor were synonymized with one another. What followed

3198-462: The chimeric material from the mainland, he subsequently named the Lord Howe material Meiolania (small roamer). This has however led to some confusion, as the etymology of Meiolania was never specified in the actual publication. Eugene S. Gaffney would later suggest that "-lania" actually translated to " butcher ", a notion later contested in the works of Juliana Sterli . Owen's identification

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3276-463: The clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the Neornithes clade, being descended from an earlier ancestor. An alternative definition does not require any members of a crown group to be extant, only to have resulted from a "major cladogenesis event". The first definition forms the basis of this article. Often, the crown group

3354-520: The closest living relatives of arthropods. Stem priapulids are other early Cambrian to middle Cambrian faunas, appearing in Chengjiang to Burgess Shale. The genus Ottoia has more or less the same build as modern priapulids , but phylogenetic analysis indicates that it falls outside the crown group, making it a stem priapulid. The name plesion has a long history in biological systematics, and plesion group has acquired several meanings over

3432-473: The club appears to be made from two segments that are fused with each other and form a spiked sheath, while in Meiolania this club is larger, formed by four distinct elements. The spikes seen on the prior tail rings continue onto the tail club, where they typically decrease in size towards the end. Other parts of the skeleton are harder to compare due to the incomplete nature of most meiolaniids, with much of

3510-517: The collected material is only present in the form of fragmentary remains too scrappy to be named or even assigned to any existing species. Due to this, much of meiolaniid diversity is only known to science in the form of various fossils designated Meiolaniidae indeterminate. However, even if fragmentary, this material nonetheless shows that members of this group were diverse and widespread throughout Cenozoic Australia. The oldest unnamed meiolaniid from Australia, known based on shell remains, osteoderms and

3588-457: The common definition of Aves and Mammalia. This has caused some confusion in the literature. The cladistic idea of strictly using the topology of the phylogenetic tree to define groups necessitates other definitions than crown groups to adequately define commonly discussed fossil groups. Thus, a host of prefixes have been defined to describe various branches of the phylogenetic tree relative to extant organisms. A pan-group or total group

3666-488: The diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group. Such fossils have been of particular importance in considering the origins of the tetrapods , mammals , and animals . The application of the stem group concept also influenced the interpretation of the organisms of the Burgess shale . Their classification in stem groups to extant phyla, rather than in phyla of their own,

3744-415: The different genera and species through the presence of marks left by the overlying scale areas, with are either present through faint grooves or raised ridges. These scale areas, at times also simply referred to as scales or scutes, are largely homologous with one another and can easily be compared. To simplify diagnosis and create a consistent naming scheme, these scale areas are labeled with capital letters,

3822-515: The divergence of the lineage from the Sauropsida to the last common ancestor of the living mammals. This group includes the synapsids as well as mammaliaforms like the morganucodonts and the docodonts ; the latter groups have traditionally and anatomically been considered mammals even though they fall outside the crown group mammals. Stem tetrapods are the animals belonging to the lineage leading to tetrapods from their divergence from

3900-536: The earliest supposed discoveries made by western scientists are said to date to the middle of the 19th century, with writings suggesting that various locals and visitors of Lord Howe Island , situated off the eastern coast of Australia, discovered the remains of large turtles. The first well supported finds came just prior to the 1880s, when a large skull of what is now known as Ninjemys was discovered in Queensland and sent to paleontologist Richard Owen . Although

3978-505: The extinct moa ) The crown group here is Neornithes , all modern bird lineages back to their last common ancestor. The closest living relatives of birds are crocodilians . If we follow the phylogenetic lineage leading to Neornithes to the left, the line itself and all side branches belong to the stem birds until the lineage merges with that of the crocodilians. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , stem group birds include

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4056-477: The eyes to the back of the head. Aside from the large horns present on the skulls, meiolaniids are also characterized by their heavily armored tails. It is believed that the entirety of the tail in meiolaniids was covered in bony rings flanked by at least two pairs of spikes. Such bone rings are known from even the most basal genus, Niolamia , and surrounds the entire circumference of the tail in it and Ninjemys . The individual rings appear to correlate directly with

4134-482: The former makes it somewhat of a wildcard in phylogenetic analysis. It has been recovered as either nesting alongside Niolamia at the base of Meiolaniidae, alongside Ninjemys at the base of the Australasian clade and as a derived genus alongside Warkalania and Meiolania . As far as stable taxa go, Ninjemys is the second basalmost genus. It is clearly united with Meiolania due to the second accessory ridge,

4212-532: The fossils was correctly identified by its collector, G. F. Bennett, Owen instead believed the skull to have belonged to a type of lizard. Combining the skull with the vertebrae of the giant monitor lizard Megalania and the foot bones of a marsupial , Owen came to believe that the bones represented a type of giant thorny devil . By 1884 better recorded fossil discoveries had been made on Lord Howe Island, with multiple shipments being sent to Owen in London. Again,

4290-432: The full bifurcating phylogeny. Stem birds perhaps constitute the most cited example of a stem group, as the phylogeny of this group is fairly well known. The following cladogram, based on Benton (2005), illustrates the concept: Crocodilia Pterosauria Hadrosauridae Stegosauria Sauropoda Tyrannosauridae Archaeopteryx Neognathae (including the extinct dodo ) Paleognathae (including

4368-442: The information stemming from Meiolania platyceps itself. The shell of Meiolania is domed rather than flattened, one of several traits indicative of a terrestrial lifestyle. However, the carapace is not quite as high as seen in today's aldabra giant tortoises and galapagos giant tortoises , instead bearing more resemblance to that of the gopher tortoise . Shell elements of Niolamia , Gaffneylania and Meiolania all show that

4446-475: The key sources of confusion regarding Niolamia . While these early publications largely treated Ameghino's and Roth's turtles as separate specimens, the former never provided a detailed diagnosis, description or even figure of his material. At the same time however, Ameghino claimed knowledge over where Roth's material originated. Recent research conducted on the history of Niolamia suggests that there never were two specimens, and that Ameghino simply missattributed

4524-651: The last surviving genus, Meiolania , which lived in Australia from the Miocene until the Pleistocene , and insular species that lived on Lord Howe Island and New Caledonia during the Pleistocene and possibly the Holocene for the latter. Meiolaniids are part of the broader grouping of Meiolaniformes , which contains more primitive turtles species lacking the distinctive morphology of meiolaniids, known from

4602-406: The material had been correctly identified as having belonged to turtles by local collectors and researchers, but was then misattributed to lizards by Owen. It was based on this material that Owen named the genus Meiolania in 1886 to include two species, M. platyceps and M. minor , believing it to be a small relative of the mainland specimen. As Owen had given the name Megalania (great roamer) to

4680-402: The most extensive look at this taxon to date. This detailed look at the type species ran in tandem with several studies examining meiolaniid fossils from other localities. 1992 saw the description of three new meiolaniid taxa in the span of a single year, consisting of the new species Meiolania brevicollis from mainland Australia, Ninjemys as a new name for Meiolania oweni and Warkalania ,

4758-464: The narrower one. Often, an (extinct) grouping is identified as belonging together. Later, it may be realized other (extant) groupings actually emerged within such grouping, rendering them a stem grouping. Cladistically , the new groups should then be added to the group, as paraphyletic groupings are not natural. In any case, stem groupings with living descendants should not be viewed as a cohesive group, but their tree should be further resolved to reveal

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4836-412: The only way to possibly determine relationships within the established Meiolania species, a trait that has been proven to be highly variable even within a single species. Doing so regardless would yield the following results, with the groupings being entirely based on the length to width ratio of the horns. In 2015, Sterli recovers M. platyceps and M. mackayi as sister taxa, with M. brevicollis being

4914-479: The origin of the stem group concept to Austrian systematist Othenio Abel (1914), and it was discussed and diagrammed in English as early as 1933 by A. S. Romer . Alternatively, the term "stem group" is sometimes used in a wider sense to cover any members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon or Anteosaurus are stem mammals in the wider sense but not in

4992-499: The phylogenetic split from the remaining amniotes (the Sauropsida ). Pan-Mammalia is thus an alternative name for Synapsida . A stem group is a paraphyletic assemblage composed of the members of a pan-group or total group, above, minus the crown group itself (and therefore minus all living members of the pan-group). This leaves primitive relatives of the crown groups , back along the phylogenetic line to (but not including)

5070-438: The point where it merges with the crocodilian lineage, along with all side branches, constitutes pan-birds. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , therefore, pan-group birds would include all dinosaurs and pterosaurs as well as an assortment of non-crocodilian animals like Marasuchus . Pan-Mammalia consists of all mammals and their fossil ancestors back to

5148-430: The potential origin of the group. The first instance of this was recognized as early 1987, when Ckhikvadzé grouped Mongolochelys , Kallokibotion and meiolaniids in a single group. In 2000 Hirayama et al. expanded on this idea, grouping Mongolochelys , sinochelyds , Otwayemys and meiolaniids together, as did subsequent authors. Chubutemys and Patagoniaemys followed in 2007 and 2011, while Peligrochelys

5226-480: The problems responsible for this varying placement can be found in the incompleteness of meiolaniid remains and their highly derived nature. After meiolaniids were recognized as turtles, Huxley suggested they were related to modern snapping turtles (genus Chelydra ), placing it in Cryptodira, the group that includes most living turtles and tortoises. While Boulenger agreed with the identification of Meiolania as

5304-573: The remains of a third meiolaniid were discovered in 1898 across the Pacific in Argentina . The precise history of these events is however poorly understood due to a large amount of conflicting information. At the time, two rivaling groups of paleontologists, one led by Florentino Ameghino and the other by Francisco Moreno , were competing in a fashion similar to the Bone Wars . Ameghino published

5382-405: The researcher concluded that Roth's turtle represented the same species, but placed both in the genus Miolania (likely a misspelling of Meiolania ). Later finds in the area would produce the taxon Crossochelys corniger , now thought to be a juvenile Niolamia and around the same time the Roth skull was elevated to the genus' neotype as Ameghino's skull could not be found. This highlights one of

5460-486: The stem group concept threatens to delay or obscure proper recognition of new higher taxa. As originally proposed by Karl-Ernst Lauterbach , stem groups should be given the prefix "stem" (i.e. Stem-Aves, Stem-Arthropoda), however the crown group should have no prefix. The latter has not been universally accepted for known groups. A number of paleontologists have opted to apply this approach anyway. Eugene S. Gaffney Too Many Requests If you report this error to

5538-442: The vertebrae, meaning that each vertebra is surrounded by a singular ring that articulates with those before and after it. The sides of the ring form bony spikes, one smaller pair that faces towards the side and one larger pair that juts out more dorsally. Some forms, namely Ninjemys and Meiolania , also preserve a tail club that tips the end of the tail and has been compared to those of glyptodonts and ankylosaurs . In Ninjemys

5616-617: The widely used total-group perspective, the Crocodylomorpha would become synonymous with the Crocodilia, and the Avemetatarsalia would become synonymous with the birds, and the above tree could be summarized as Crocodilia Birds An advantage of this approach is that declaring Theropoda to be birds (or Pan-aves ) is more specific than declaring it to be a member of the Archosauria, which would not exclude it from

5694-491: The years. One use is as "nearby group" (plesion means close to in Greek ), i.e. sister group to a given taxon , whether that group is a crown group or not. The term may also mean a group, possibly paraphyletic , defined by primitive traits (i.e. symplesiomorphies ). It is generally taken to mean a side branch splitting off earlier on the phylogenetic tree than the group in question. Placing fossils in their right order in

5772-540: Was a connection to lizards, with Meiolania possibly representing a relative to both reptile groups. For this new clade, Owen coined the name Ceratosauria, unaware the name was already occupied by a group of dinosaurs as defined by Othniel Charles Marsh in 1884. In spite of Owen's conviction, more and more researchers published on the turtle identity of Meiolania . George Albert Boulenger placed Meiolania in Pleurodira and Arthur Smith Woodward officially split

5850-438: Was a long, uninterrupted period of fossil collection on Lord Howe Island, providing a massive quantity of fossil material. Although excavations were productive, this time period was relatively uneventful in regards to taxonomy, with the only Australasian Meiolania species named in this period being M. mackayi from Walpole Island south of New Caledonia in 1925. Parallel to the later stages of this initial burst of revisions,

5928-430: Was described in 2012. Both Mongolochelys and Peligrochelys show scale areas similar to those characteristic for meiolaniids and several other anatomical features have been observed uniting these Mesozoic turtles with meiolaniids. Sterli and de la Fuente conclude that the presence of well defined scale areas present on the skull may have been plesiomorphic for all turtles, and was simply lost and re-evolved repeatedly in

6006-430: Was developed by Willi Hennig , the formulator of phylogenetic systematics , as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen . It

6084-601: Was soon criticized by other scientists in London, who agreed with the Australian researchers in that these remains were actually those of turtles, not lizards. Just one year after Meiolania was named, Thomas Henry Huxley published a paper correcting Owen and naming the material Ceratochelys sthenurus , to which Huxley further assigned the Queensland skull. Owen meanwhile, who had received more material from Australia, slightly amended his prior research. While now also recognizing some turtle affinities, Owen maintained that there

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