Chelidae is one of three living families of the turtle suborder

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 ...

, and are commonly called Austro-South American side-neck turtles. The family is distributed in Australia,

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torres ...

, parts of

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guinea. In ...

, and throughout most of South America. It is a large family of turtles with a significant fossil history dating back to the Cretaceous. The family is entirely

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

n in origin, with no members found outside Gondwana, either in the present day or as a fossil.Georges, A. & Thomson, S. (2006). "Evolution and Zoogeography of Australian freshwater turtles". In: Merrick, J. R.; Archer, M.; Hickey, G. & Lee, M. (eds.) ''Evolution and Zoogeography of Australasian Vertebrates''. Sydney: Australia.

Description

Like all pleurodirous turtles, the chelids withdraw their necks sideways into their shells, differing from cryptodires that fold their necks in the vertical plane. They are all highly aquatic species with webbed feet and the capacity to stay submerged for long periods of time. The snake-necked species (genera '' Chelus'', '' Chelodina'', and '' Hydromedusa'') are largely strike-and-gape hunters or foragers feeding on fish, invertebrates, and gastropods. The short-necked forms are largely herbivorous or molluscivorous, but are also opportunistic, with several species having specialized to eating fruits. The highly aquatic nature of the group is typified by the presence of

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, an ...

l breathing in some species of the genera '' Elseya'' and '' Rheodytes''.Gordos, M. A.; Franklin, C. E. & Limpus, C. J. (2004). "Effect of water depth and water velocity upon the surfacing frequency of the bimodally respiring freshwater turtle, ''Rheodytes leukops''". ''The Journal of Experimental Biology''. 207: 3099-3107. However, some species, such as the eastern long-neck turtle ('' Chelodina longicollis'') from Australia spend significant periods of time on land and are considered highly

terrestrial Terrestrial refers to things related to land or the planet Earth. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on or near the ground, as opposed to ...

. The smaller members of the family include the Macleay River turtle ('' Emydura macquarii'') at around 16 cm, twist-necked turtle ('' Platemys platycephala'') at 18 cm and the western swamp turtle ('' Pseudemydura umbrina'') at 15 cm, whereas the larger species such as the ''mata mata'' ('' Chelus fimbriata'') and the white-throated snapping turtle (''

Elseya albagula ''Elseya albagula'', commonly known as the white-throated snapping turtle, is one of the largest species of chelid turtles in the world, growing to about carapace length. The species is endemic to south-eastern Queensland, Australia, in the ...

'') both exceed 45 cm in shell length.Thomson, S.; Georges, A. & Limpus, C. (2006). "A New Species of Freshwater Turtle in the Genus ''Elseya'' (Testudines: Chelidae) from Central Coastal Queensland, Australia". ''Chelonian Conservation and Biology''. 5 (1): 74-86. Chelids exhibit XX/XY genetic sex determination, in contrast to most other turtles, which have

temperature-dependent sex determination Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. It is only observed in reptiles and teleost fish ...

Shell morphology

Members of Chelidae have unique shell morphology. The

carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the under ...

often has reduced surface exposure of neural bones, or even none at all.Thomson, S. & Georges, A. (1996). "Neural bones in chelid turtles". ''Chelonian Conservation and Biology'' 2: 82-86. This is due to less requirement for enlarged

longissimus dorsi The longissimus ( la, the longest one) is the muscle lateral to the semispinalis muscles. It is the longest subdivision of the erector spinae muscles that extends forward into the transverse processes of the posterior cervical vertebrae. Structur ...

muscles in side-necked turtles.Thomson S. (2003)
"Long necks, flat heads and the evolution of piscivory"
World Chelonian Trust. The inside of the carapace is often heavily buttressed. This has sometimes been seen as a defense mechanism, that is it increases the strength of the shell against biting force, however Thomson (2003) demonstrated it is linked to feeding methods and the prevention of internal torsion of the shell. Chelids also lack mesoplastra, which separates them from the

Pelomedusidae :''Alternatively, "Pelomedusidae" may refer to the Pelomedusoidea. See below for details.'' Pelomedusidae is a family of freshwater turtles endemic to sub-Saharan Africa, including Madagascar, São Tomé, and the Seychelles(Although this pop. ...

The cervical scute is usually present, though it is absent in some species of '' Elseya'' and ''

Myuchelys The ''Myuchelys'' is a genus of turtles, the Australian saw-shelled turtles, in the family Chelidae and subfamily Chelodininae. They inhabit the headwaters and tributaries of rivers within their range and this led to the name ''Myuchelys'', whi ...

''. Otherwise, the carapace has the usual complement of four costals, five vertebrals and twelve marginals (per side). Internally, the carapace is made of eight pleurals (per side), eleven peripherals (per side), a nuchal at the front and a suprapygal and pygal at the rear of the shell. As noted earlier, neurals, although always present, often exist as subsurface elements above the vertebral column. Pu plastron

The plastron of chelids does not contain any hinges as can appear in some cryptodire turtles. The scute pattern is a unique feature of the

and can be used to immediately identify a shell as belonging to this suborder. All cryptodires have 12 plastral scutes, whereas pleurodires have thirteen. The extra scute is called the intergular. The rest of the scutes and the skeletal structure beneath them are the same as all turtles: paired gulars, humerals, pectorals, abdominals, and anals. The skeletal elements consist of a single entoplaston, as well as paired epiplastra, entoplastra, hyoplastra, hypoplastra and xiphiplastra (Pritchard & Trebbau, 1984).Pritchard, Peter C. H. & Trebbau, Pedro (1984). '' The Turtles of Venezuela''. Society for the Studies of Amphibians and Reptiles: 403 pp.

Evolutionary history

The oldest records of Pan-Chelidae (the clade containing Chelidae and all other species more closely related to Chelidae than other pleurodires) first appear in the mid Cretaceous in South America and Australia, represented by '' Prochelidella cerrobarcinae'' from the

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 Cenoma ...

of Argentina, which dates from 118 to 110 million years ago, and indeterminate remains from the

Griman Creek Formation The Griman Creek Formation is a geological formation in northern New South Wales and southern Queensland, Australia whose strata date back to the Albian-Cenomanian of the Early-Late Cretaceous.Bell et al., 2019 It is most notable being a major s ...

, of New South Wales, Australia, dating to around 100 million years ago.

Classification

A number of theories of the relationships within the large chelid family have been posited. Using shared derived characters, an early attempt in the 1970s used strict

parsimony Parsimony refers to the quality of economy or frugality in the use of resources. Parsimony may also refer to * The Law of Parsimony, or Occam's razor, a problem-solving principle ** Maximum parsimony (phylogenetics), an optimality criterion in p ...

to determine the three long-necked genera ('' Chelodina'', '' Chelus'', and '' Hydromedusa'') were each other's closest relatives.Gaffney, E. S. (1977). "The side-necked turtle family Chelidae: a theory of relationships using shared derived characters". ''American Museum Novitates''. 2620: 1-28. This was accepted for some time, but brought into scrutiny,Pritchard, P. C. H. (1984). "Piscivory in turtles, and evolution of the long-necked Chelidae". in Ferguson, M. W. (ed) ''The Structure, Development and Evolution of Reptiles''. Zoological Society of London, Symposium. 52: 87-110. because the major differences between the genera showed they all appeared to have evolved independently of each other, hinging on the fact that although they had long necks, how they used them and their structures were different. A number of additional data sets were developed that used electrophoresis and nuclear and mtDNA analysis; these all agreed on the independent evolution of the three long-necked clades.Seddon, J.; Georges, A.; Baverstock, P. & McCord, W. (1997). "Phylogenetic relationships of chelid turtles (Pleurodira: Chelidae) based on mitochondrial 12S rRNA gene sequence variation". ''Molecular Phylogenetics and Evolution''. 7: 55-61. This was culminated in a reanalysis of the morphological data which demonstrated the convergence of the clades on a sweep of distinctive features needed for their piscivorous diets,Thomson S. (2003). "Long necks, flat heads and the evolution of piscivory". World Chelonian Trust Thomson, 2000.Thomson S. A. (2000). "On the identification of the holotype of ''Chelodina oblonga'' (Testudinata: Chelidae) with a discussion of the taxonomic implications". ''Chelonian Conservation and Biology''. 3: 745-749. The subfamilies within Chelidae show the monophyly of the majority of the South American species and all the Australian species, with the far more ancient ''Hydromedusa'' as sister taxon to both these other groups. The family Chelidae contains about 60 species within around twenty genera:Georges, A.; Birrell, J.; Saint, K. M.; McCord, W. & Donnellan, S. C. (1998). "A phylogeny for side-necked turtles (Chelonia: Pleurodira) based on mitochondrial and nuclear gene sequence variation". ''Biological Journal of the Linnean Society''. 67: 213-246. Taxonomy after TTWG 2021 *

Stem-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

taxa **Genus †'' Bonapartemys'' Lapparent de Broin & de la Fuente, 2001Broin, F. de & de la Fuente, M. S. (2001). "Oldest world Chelidae (Chelonii, Pleurodira), from the Cretaceous Patagonia, Argentina". ''Palaeontology'' 333: 463-470.

Bajo Barreal Formation The Bajo Barreal Formation is a geological formation in the Golfo San Jorge Basin of Chubut and Santa Cruz, Argentina whose strata date back to the Middle Cenomanian to Late Turonian. The formation was first described by Teruggi & Rossetto in ...

, Argentina, Late Cretaceous ( Cenomanian-

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded by ...

) **Genus †'' Linderochelys'' de la Fuente et al., 2007 Río Neuquén Subgroup, Argentina, Late Cretaceous (Turonian-

Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by t ...

) **Genus †'' Lomalatachelys'' Lapparent de Broin & de la Fuente 2001

Bajo de la Carpa Formation The Bajo de la Carpa Formation is a geologic formation of the Neuquén Basin that crops out in northern Patagonia, in the provinces of Río Negro and Neuquén, Argentina. It is the oldest of two formations belonging to the Río Colorado Subgro ...

, Argentina, Late Cretaceous (

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. T ...

) **Genus †'' Palaeophrynops'' Lapparent de Broin & de la Fuente 2001

Los Alamitos Formation The Los Alamitos Formation is a geological formation of the North Patagonian Massif in Rio Negro Province, northwestern Patagonia, Argentina, whose strata date back to the Late Cretaceous ( Late Campanian to Maastrichtian). Dinosaur remains are ...

, Argentina, Late Cretaceous (late

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 ...

-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 ...

) **Genus †'' Prochelidella'' Lapparent de Broin & de la Fuente 2001

, Argentina, Early Cretaceous (

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) ...

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

)

Candeleros Formation The Candeleros Formation (formerly known as the Candeleros Member of the "Río Limay Formation") is a geologic formation that crops out in the Río Negro, Neuquén, and Mendoza provinces of northern Patagonia, Argentina. It is the oldest formati ...

, Argentina, Cenomanian Bajo Barreal Formation, Argentina, Cenomanian-Turonian

Portezuelo Formation The Portezuelo Formation is a geologic formation of Late Cretaceous ( Late Turonian to Early Coniacian) age, outcropping in the Mendoza, Río Negro and Neuquén provinces of Argentina.Salamanchelys'' Bona, 2006

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 diversi ...

, Argentina,

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''palaió ...

(

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 Cretaceou ...

) **Genus †'' Parahydraspis'' Wieland 1923Wieland, G. R. (1923). "A new Parana Pleurodiran". ''American Journal of Science''. 5 (25): 1-15.

Ituzaingó Formation The Ituzaingó Formation ( es, Formación Ituzaingó), in older literature also described as Entre Ríos or Entrerriana Formation, is an extensive geological formation of Late Miocene (Tortonian, or Huayquerian in the SALMA classification) age in ...

, Argentina, Miocene (

Huayquerian The Huayquerian ( es, Huayqueriense) age is a period of geologic time (9.0–6.8 Ma) within the Late Miocene epoch of the Neogene, used more specifically within the SALMA classification. It follows the Mayoan and precedes the Montehermosan age. ...

) ** Family Chelidae Gray, 1831Gray, J. E. (1831). ''Synopsis Reptilium Or Short Descriptions of the Species of Reptiles. Part 1. Cataphracta, Tortoises, Crocodiles, and Enaliosaurians''. London. 85 pp. (Crown group) *** Subfamily Chelodininae Baur 1893Baur, Georg (1893). "Notes on the classification of the Cryptodira". ''American Naturalist''. 27 :672–674. **** Genus †'' Birlimarr'' Megirian & Murray 1999Megirian, D. & Murray, P. (1999). "Chelid turtles (Pleurodira, Chelidae) from the Miocene Camfield Beds, Northern Territory of Australia, with a description of a new genus and species". ''The Beagle'' (Records of the Museums and Art Galleries of the Northern Territory). 15: 75–130. Camfield Beds, Northern Territory, Australia, Middle

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recent" ...

**** Genus '' Chelodina'' Fitzinger 1826 – Australian snake-necked turtles **** Genus '' Elseya'' Gray 1867 – Australian snapping turtlesGray, J. E. (1867). "Description of a new Australian tortoise (''Elseya latisternum'')". ''Annals and Magazine of Natural History''. (3) 20: 43-45. **** Genus ''

Emydura ''Emydura'', the Australian short-necked turtles, are a genus of turtles in the family Chelidae. It was paraphyletic with '' Elseya''. Consequently, it was split into two genera ''Myuchelys'' and ''Elseya'' by Thomson & Georges, 2009.Thomson, S ...

'' Bonaparte 1836 – Australian short-necked turtles **** Genus ''Elusor'', Cann & Legler, 1994Cann, J. & Legler, J. M. (1994). "The Mary River Tortoise: a new genus and species of short-necked chelid from Queensland, Australia (Testudines; Pleurodira)". ''Chelonian Conservation and Biology''. 1 (2): 81-96. – Mary River turtle **** Genus '' Flaviemys'' Le et al., 2013Le, M.; Reid, B. N.; McCord, W. P.; Naro-Maciel, E.; Raxworthy, C. J.; Amato, G. & Georges A. (2013). "Resolving the phylogenetic history of the short-necked turtles, genera ''Elseya'' and ''Myuchelys'' (Testudines: Chelidae) from Australia and New Guinea". ''Molecular Phylogenetics and Evolution''. 68 (2013) 251–258. yellow-faced saw-shelled turtles **** Genus ''

'' Thomson & Georges 2009Thomson, S. & Georges, A. (2009). "''Myuchelys'' gen. nov. — a new genus for ''Elseya latisternum'' and related forms of Australian freshwater turtle (Testudines: Pleurodira: Chelidae)". ''Zootaxa''. 2053: 32–42. – Australian saw-shelled turtles **** Genus '' Rheodytes'' Legler & Cann, 1980Legler, J. M. & Cann, J. (1980). "A new species of chelid turtle from Queensland, Australia". ''Contributions to Science'', Natural History Museum of Los Angeles County. 324: 1-18. – Fitzroy River turtles *** Subfamily Chelinae Gray, 1825Gray, John Edward (1825). "A synopsis of the genera of reptiles and amphibia, with a description of some new species". ''Annals of Philosophy''. (2) 10: 193–217. **** Genus '' Chelus'' Duméril 1806 – matamata turtles **** Genus '' Acanthochelys'' Gray, 1873Gray, J. E. (1873). "Observations on chelonians, with descriptions of new genera and species". ''Annals and Magazine of Natural History''. (4) 11: 289-308. – South American side-necked swamp turtles **** Genus '' Mesoclemmys'' – including gibba turtle **** Genus '' Phrynops'' – toad-headed turtles **** Genus ''Platemys'' Wagner 1830 – twist-necked turtles **** Genus ''Ranacephala'' McCord, Joseph-Ouni & Lamar 2001 – Hoge's side-necked turtle **** Genus '' Rhinemys'' – red-headed side-necked turtle *** Subfamily Hydromedusinae Baur, 1893Baur, Georg. (1893). "Notes on the classification and taxonomy of the Testudinata". ''Proceedings of the American Philosophical Society''. 31: 210–225. **** Genus '' Hydromedusa'' Wagler 1830 – South American snake-necked turtles **** Genus †'' Yaminuechelys'' de la Fuente et al. 2001

Anacleto Formation The Anacleto Formation is a geologic formation with outcrops in the Argentine Patagonian provinces of Mendoza, Río Negro, and Neuquén. It is the youngest formation within the Neuquén Group and belongs to the Río Colorado Subgroup. Formerl ...

, Argentina, Santonian-Campanian

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 ...

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 format ...

, Los Alamitos Formation, Argentina, Campanian-Maastrichtian, Salamanca Formation, Roca Formation, Argentina, Paleocene (Danian) *** Subfamily Pseudemydurinae Zhang et al., 2017Zhang, X.; Unmack, P. J.; Kuchling, G.; Wang, Y. & Georges, A. (October 2017). "Resolution of the enigmatic phylogenetic relationship of the critically endangered Western Swamp Tortoise ''Pseudemydura umbrina'' (Pleurodira: Chelidae) using a complete mitochondrial genome". ''Molecular Phylogenetics and Evolution''. 115: 58-61. **** Genus '' Pseudemydura'' Siebenrock 1901Seibenrock, F. (1901). "Beschreibung einer neuen schildkrotengattung aus der familie Chelydidae aus Australien: ''Pseudemydura''". ''Anzeiger der Akademie der Wissenschaften in Wien''. 38: 248-251. – western swamp tortoise

Phylogeny

Relationships of the living forms based on Georges et al., 2014. The species in the Chelidae family are distributed across Australia, New Guinea, and South America. Over time they were required to disperse out of concerns of food shortage, habitat destruction, and weather disruptions. In all of these warmer climates, they can be found in turbid waters covered by muck and the root-mats of underwater vegetation. The waters that they are found in often lack large species of fish that would put them at risk of predation.

References

External links and further reading

Chelidae

Gondwanan turtle site
{{Testudines Taxa named by John Edward Gray Turtle families Extant Albian first appearances