Meiolaniidae

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 or prior to the Middle Jurassic. They are best known from 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 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 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 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 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 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, 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 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 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 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 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 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.