Meiolaniformes is an extinct

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

of stem-group

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

s, defined as all taxa more closely related to ''

Meiolania ''Meiolania'' ("small roamer") is an extinct genus of meiolaniid stem-turtle native to Australasia from the Middle Miocene to Late Pleistocene and possibly Holocene. It is best known from fossils found on Lord Howe Island, though fossils are know ...

'' than to

Cryptodira The Cryptodira ('' el, hidden neck'') are a suborder of Testudines that includes most living tortoises and turtles. Cryptodira differ from Pleurodira (side-necked turtles) in that they lower their necks and pull the heads straight back into the ...

and

Pleurodira The Pleurodira are one of the two living suborders of turtles, the other being the Cryptodira. The division between these two suborders represents a very deep evolutionary divide between two very different types of turtles. The physical differen ...

. It is known from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

to the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Oceania Oceania (, , ) is a region, geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern Hemisphere, Eastern and Western Hemisphere, Western hemispheres, Oceania is estimated to have a land area of ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

. Some

Eurasian Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

taxa have been suggested to be part of the group, but this is disputed. The oldest member of Meiolaniformes is Australian Early Cretaceous '' Otwayemys''.

Taxonomy

The clade as currently defined contains the following taxa: * †''

Chubutemys ''Chubutemys'' was an extinct genus of meiolaniform turtle. It lived during the Early Cretaceous of Argentina, around the Albian-Aptian border, within the Puesto La Paloma Member of the Cerro Barcino Formation. It is known from most of the ske ...

'' Gaffney et al. 2007 -

Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ago), a ...

Cerro Barcino Formation The Cerro Barcino Formation (also known as the Gorro Frigio Formation) is a geological formation in South America whose strata span the Early Cretaceous to the earliest Late Cretaceous. The top age for the formation has been estimated to be Cenoman ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

* †'' Otwayemys'' Gaffney et al. 1998 - Aptian,

Eumeralla Formation The Eumeralla Formation is a geological formation in Victoria, Australia whose strata date back to the Early Cretaceous. It is Aptian to Albian in age. Dinosaur remains are among the fossils that have been recovered from the formation, particularl ...

* †''

Patagoniaemys ''Patagoniaemys'' is an extinct genus of stem turtle which existed in central Patagonia, Chubut Province, Argentina during the late Cretaceous epoch (Campanian to Maastrichtian age). It is known from skull fragments and several postcranial elemen ...

'' Sterli and de la Fuente 2011 Upper

Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campanian s ...

-Lower

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

La Colonia Formation The La Colonia Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel et al., 2004, pp.600-604 Originally thou ...

, Argentina * †'' Peligrochelys'' Sterli and de la Fuente 2011

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretaceous� ...

Salamanca Formation The Salamanca Formation is a geologic formation in the Golfo San Jorge Basin of central Patagonia that yields well-preserved, well-dated fossils from the early Paleocene. Studies of these fossils are providing new data on plant and animal diversit ...

, Argentina * †'' Trapalcochelys'' Sterli et al. 2013 Upper Campanian,

Allen Formation The Allen Formation is a geological formation in Argentina whose strata date back to the Late Cretaceous (middle Campanian to early Maastrichtian.Salgado et al., 2007 Dinosaur remains are among the fossils that have been recovered from the formati ...

, Argentina * †

Meiolaniidae Meiolaniidae is an extinct family of large, probably herbivorous stem-group turtles with heavily armored heads and tails known from South America and Australasia. Though once believed to be cryptodires, they are not closely related to any living ...

Lydekker 1887,

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

, Argentina and Australia and Oceania It has also been suggested that '' Mongolochelys'', '' Sichuanchelys'', and ''

Kallokibotion ''Kallokibotion'' is an extinct genus of stem-turtle from the Upper Cretaceous (Maastrichtian, 86–66 million years ago), known from fossils found in Romania. One species is known, ''Kallokibotion bajazidi'', which was named by Franz Nopcsa aft ...

'' from the Late Cretaceous of Mongolia, China and Europe respectively are part of this group, but other studies find these taxa in a more derived position nearer crown

Testudines Turtles are an order (biology), order of reptiles known as Testudines, characterized by a special turtle shell, shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) an ...

. Regardless, all taxa are members of

Perichelydia Perichelydia (from Greek ''peri'' "near" and ''chelys'' "turtle") is a clade within Pantestudines (turtles and their extinct relatives) known from the Middle Jurassic to Holocene. Alongside crown group Testudines, it also contains Helochelydrid ...

References

{{Taxonbar, from=Q21226122