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 (2 ft 4 in – 6 ft 7 in) 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.

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 carapace with spiky edges, osteoderm-covered front limbs, a head adorned by massive cow-like horns and a tail encased by spiked tail rings and tipped by a large bony club. It has been hypothesized that many of these features could have been used either in self-defense or in intraspecific combat during the mating season. Furthermore, the horns could have served a role during foraging, helping the animal brush aside foliage while grazing. The discovery of fossil nests and certain adaptations against sand entering its nasal cavity indicate that they spent at least some time in arid regions or on the beaches of the islands they inhabited.

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.

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.

In 1884 turtle fossils once again found their way into the possession of FitzGerald, who proceeded to send the remains to Owen in London. It is noted that the collection of Meiolania remains seemingly reached a highpoint around this time, yet was poorly recorded in contrast to the well known history of less prolific expeditions. Multiple researchers appear to have been actively collecting turtle fossils at the time, including FitzGerald and Wilkinson who were seemingly unaware of each other's efforts despite working for the same institution. In London meanwhile, Owen noted that the fossils of Lord Howe Island were similar to a skull discovered several years prior in Queensland, which he had attributed to the giant squamate Megalania (at the time thought to be a giant relative of the thorny devil rather than a monitor lizard). What has been noted as strange about Owen's conclusion is that he identified the fossils as those of a lizard despite the fact that multiple researchers in correspondence with him had already recognized them as belonging to a turtle. Owen saw the discovery of the Lord Howe Island material as evidence for a smaller relative of Megalania, which he subsequently named Meiolania. BMNH R675, an incomplete and damaged skull embedded in hardened calcarenite, was chosen to serve as the holotype for the genus and although its precise age and location is not known, Eugene S. Gaffney suggests it may have come from the 100,000 to 120,000 year old rocks of Ned's Beach. 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.

Additional material was then described in 1889 from Gulgong, New South Wales, and in 1893 from Coolah, New South Wales. These instances were thought to correspond to a Pliocene and Pleistocene age respectively and recorded by Robert Etheridge, Junior. Etheridge initially intended to write a detailed description on Meiolania after becoming personally invested and ensuring the continued collection of material. However his focus eventually shifted and his work was instead continued by Charles Anderson. Around the same time the remains of a meiolaniid turtle were discovered in Argentina, named Niolamia argentina by Florentino Ameghino. While these remains were briefly considered to be a species of Meiolania and may have in fact originally intended to be named as a species of the genus, they would eventually found to be distinct enough to retain the original name.^{[citation needed]}