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Chelidae is one of three living families of the turtle suborder
Pleurodira The Pleurodira are one of the two living suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known rank ...
, and are commonly called Austro-South American side-neck turtles. The family is distributed in
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 ...

Australia
,
New Guinea New Guinea (; Hiri Motu Hiri Motu, also known as Police Motu, Pidgin Motu, or just Hiri, is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign ...

New Guinea
, parts of
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...

Indonesia
, 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 () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...

Gondwana
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
cryptodire 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 s ...
s 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 ''Chelus'' is a genus of freshwater turtles found in South America. Formerly considered to be a monotypic genus, it now consists of two species after ''Chelus orinocensis'' was identified in 2020 from a genomic analysis. Species *''Chelus fimbri ...
'', ''
Chelodina ''Chelodina'', collectively known as snake-necked turtles, is a large and diverse genus of long-necked Chelidae, chelid turtles with a complicated Biological nomenclature, nomenclatural history. Although in the past, ''Macrochelodina'' and ''Macr ...
'', 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 cloacal 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 animal, terrestrial. 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, Chelus fimbriata'') and the white-throated snapping turtle (''Elseya albagula'') 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 XY sex-determination system, XX/XY genetic sex determination, in contrast to most other turtles, which have temperature-dependent sex determination.


Shell morphology

Members of Chelidae have unique shell morphology. The carapace 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 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. The cervical scute is usually present, though it is absent in some species of ''Elseya'' and ''Myuchelys''. 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. The plastron of chelids does not contain any hinges as can appear in some
cryptodire 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 s ...
turtles. The scute pattern is a unique feature of the
Pleurodira The Pleurodira are one of the two living suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known rank ...
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. & Pedro Trebbau, Trebbau, Pedro (1984). ''The Turtles of Venezuela''. Society for the Studies of Amphibians and Reptiles: 403 pp.


Evolutionary history

The oldest records 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, Prochelidella cerrobarcinae'' from the Cerro Barcino Formation of Argentina, which dates from 118 to 110 million years ago, and indeterminate remains from the Griman Creek Formation, 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 Occam's razor, parsimony to determine the three long-necked genera (''
Chelodina ''Chelodina'', collectively known as snake-necked turtles, is a large and diverse genus of long-necked Chelidae, chelid turtles with a complicated Biological nomenclature, nomenclatural history. Although in the past, ''Macrochelodina'' and ''Macr ...
'', ''
Chelus ''Chelus'' is a genus of freshwater turtles found in South America. Formerly considered to be a monotypic genus, it now consists of two species after ''Chelus orinocensis'' was identified in 2020 from a genomic analysis. Species *''Chelus fimbri ...
'', 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 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, Argentina, Late Cretaceous (Cenomanian-Turonian) **Genus †''Linderochelys'' de la Fuente et al., 2007 Río Neuquén Subgroup, Argentina, Late Cretaceous (Turonian-Coniacian) **Genus †''Lomalatachelys nuequina, Lomalatachelys'' Lapparent de Broin & de la Fuente 2001 Bajo de la Carpa Formation, Argentina, Late Cretaceous (Santonian) **Genus †''Palaeophrynops'' Lapparent de Broin & de la Fuente 2001 Los Alamitos Formation, Argentina, Late Cretaceous (late Campanian -lower Maastrichtian) **Genus †''Prochelidella'' Lapparent de Broin & de la Fuente 2001 Cerro Barcino Formation, Argentina, Early Cretaceous (Aptian-Albian) Candeleros Formation, Argentina, Cenomanian Bajo Barreal Formation, Argentina, Cenomanian-Turonian Portezuelo Formation, late Turonian – early Coniacian **Genus †''Salamanchelys'' Bona, 2006 Salamanca Formation, Argentina, Paleocene (Danian) **Genus †''Parahydraspis'' Wieland 1923Wieland, G. R. (1923). "A new Parana Pleurodiran". ''American Journal of Science''. 5 (25): 1-15. Ituzaingó Formation, Argentina, Miocene (Huayquerian) ** 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 **** Genus ''
Chelodina ''Chelodina'', collectively known as snake-necked turtles, is a large and diverse genus of long-necked Chelidae, chelid turtles with a complicated Biological nomenclature, nomenclatural history. Although in the past, ''Macrochelodina'' and ''Macr ...
'' 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'' Bonaparte 1836 – Australian short-necked turtles **** Genus Mary River turtle, ''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 ''Myuchelys'' 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 ''Chelus'' is a genus of freshwater turtles found in South America. Formerly considered to be a monotypic genus, it now consists of two species after ''Chelus orinocensis'' was identified in 2020 from a genomic analysis. Species *''Chelus fimbri ...
'' 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 Twist-necked turtle, ''Platemys'' Wagner 1830 – twist-necked turtles **** Genus Hoge's side-necked turtle, ''Ranacephala'' McCord, Joseph-Ouni & Lamar 2001 **** 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, Argentina, Santonian-Campanian La Colonia Formation, Allen Formation, Los Alamitos Formation, Argentina, Campanian-Maastrichtian, Salamanca Formation, Roca Formation, Argentina, 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 Chelidae, Taxa named by John Edward Gray Turtle families Extant Albian first appearances Albian taxonomic families Cenomanian taxonomic families Turonian taxonomic families Coniacian taxonomic families Santonian taxonomic families Campanian taxonomic families Maastrichtian taxonomic families Danian taxonomic families Selandian taxonomic families Thanetian taxonomic families Ypresian taxonomic families Lutetian taxonomic families Bartonian taxonomic families Priabonian taxonomic families Rupelian taxonomic families Chattian taxonomic families Aquitanian taxonomic families Burdigalian taxonomic families Langhian taxonomic families Serravallian taxonomic families Tortonian taxonomic families Messinian taxonomic families Zanclean taxonomic families Piacenzian taxonomic families Gelasian taxonomic families Calabrian taxonomic families Ionian taxonomic families Tarantian taxonomic families Holocene taxonomic families