Meiolania

Comparison between the horn cores of a M. platyceps (AM F16866) and M. mackayi (holotype AM Fl7720) specimen

The genus was erected in 1886 based on remains found on Lord Howe Island, which Richard Owen assigned to the two species M. platyceps and M. minor (now a synonym of the former).[1] These were the first good meiolaniid remains, and were used to show that the first known remains of a related animal, a species from Queensland now known as Ninjemys oweni (which was assigned to Meiolania until 1992), did not belong to lizards as initially thought, but to turtles.[5] Woodward sank Niolamia argentina into Meiolania, but this was not accepted by later authors.

The species of the genus may be summarized as

• Meiolania brevicollis Megirian, 1992
• Meiolania platyceps Owen, 1886
• Meiolania mackayi Anderson, 1925

In New Caledonia, M. mackayi was described from Walpole Island in 1925. It was smaller and less robust than M. platyceps.[6] Meiolania remains are also known from the Pindai Caves, Grande Terre, and from Tiga Island. M. brevicollis was described in 1992 from the mid-Miocene Camfield Beds of northern Australia, and differed from M. platyceps in having a flatter skull and other horn proportions.[7]

A second undescribed species of Meiolania from mainland Australia is known from the Wyandotte Creek locality in Queensland, dated to the Late Pleistocene, consisting of three horn cores and a caudal vertebra, noted to be "unusually large" in size. This species is referred to as M. cf platyceps, as the remains are most similar to M. platyceps but are not diagnostic beyond genus level.[8][9]

Holocene remains of turtles from Vanuatu found in Lapita culture middens were referred to Meiolania in 2010 as the new species ?M. damelipi.[10] However, this has been disputed, with other authors stating that the remains appeared to be non-meiolaniiform, and no parietal horns, a distinctive characteristic of Meiolania, have been found at any locality in Vanuatu, despite being one of the most common finds on Walpole and Lord Howe. The long bone morphology agrees more closely with a tortoise identification, a group which has otherwise not been reported from the South Pacific or Australasia.[11][12] Further remains, attributable to ?M. damelipi or a closely related form, have been found in various parts of the Fijian archipelago, including Viti Levu, Vanua Levu, and some smaller islands.[13][14] ?M. damelipi is the yongest species assigned to Meiolania, with the youngest remains dating to around 1000 BCE.[15]

Meiolania had an unusually shaped skull that sported many knob-like and horn-like protrusions. Two large horns faced sideways, and would have prevented the animal fully withdrawing its head into its shell. The tail was protected by armored 'rings', and sported thorn-like spikes at the end.[16] The body form of Meiolania may be viewed as having converged towards those of dinosaurian ankylosaurids and xenarthran glyptodonts.

There are two species of Meiolania known from the Australian continent: M. brevicollis and an unnamed species. The unnamed species could reach 2 metres (6.6 ft) in carapace length, making it the second-largest known terrestrial turtle or tortoise, surpassed only by Megalochelys atlas from Asia, which lived in the Pleistocene.[15] The smallest species in turn was M. mackayi from New Caledonia, with a carapace length of 70 centimetres (2.3 ft). Another insular species is known from Lord Howe Island, M. platyceps. It was a huge turtle, about 100 cm (3.3 ft) in carapace length[15] and probably more than 3 m (9.8 ft) in total body length.[4] Largest specimens of ?M. damelipi had carapaces of 100–135 cm (3.28–4.43 ft) long.[12][15]

Meiolania is thought to have fed on plants, and they and other meiolaniids have been generally assumed to be fully terrestrial, though acceptance of this is not universal.[17] Fossil Meiolania eggs have been reported from Lord Howe, assigned to the oogenus Testudoolithus lordhowensis. The eggs are large and spherical, approximately 5.4 cm in diameter, and around 800 μm thick. Like the eggs of modern turtles, they are made of aragonite. The eggs were likely deposited within an excavated hole nest.[18]

It is thought that postglacial sea level rise may have contributed to the extinction of M. platyceps on Lord Howe Island, as the area of the current island is much smaller than that exposed during the Pleistocene. They were absent when the islands were first explored by Europeans, who were likely the first humans to discover the islands. The extinction of Meiolania in mainland Australia and in Melanesia has been postulated to be due to human activity.[10][4][12]

• 
  Front view of M. platyceps fossil, Lord Howe Island museum
• 
  The tail of Meiolania platyceps (AMNH 29076)
• 
  Meiolania platyceps, Lord Howe Island Maritime Museum
• 
  The skull of Meiolania platyceps (AMNH 29076)

• Biodiversity of New Caledonia
• Holocene extinction

Wikimedia Commons has media related to Meiolania.

Wikispecies has information related to Meiolania.

• Meiolania platyceps Owen (The Australian Museum; photo)