Chelidae Temporal range: | |
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Chelus fimbriatus | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Reptilia |
Order: | Testudines |
Suborder: | Pleurodira |
Family: | Chelidae Gray, 1831 [1] |
Genera | |
See text |
Chelidae is one of three living families of the turtle suborder Pleurodira, and are commonly called Austro-South American side-neck turtles. [2] The family is distributed in Australia, New Guinea, parts of 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 Gondwanan in origin, with no members found outside Gondwana, either in the present day or as a fossil. [3]
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 cloacal breathing in some species of the genera Elseya and Rheodytes . [4] 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.
The smaller members of the family include the Macleay River turtle ( Emydura macquarii ) at around 16 cm, [5] 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 ) both exceed 45 cm in shell length. [6]
Chelids exhibit XX/XY genetic sex determination, in contrast to most other turtles, which have temperature-dependent sex determination. [7]
Members of Chelidae have unique shell morphology. The carapace often has reduced surface exposure of neural bones, or even none at all. [8] This is due to less requirement for enlarged longissimus dorsi muscles in side-necked turtles. [9]
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) [9] 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. [8]
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 Pleurodira 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 entoplastron, as well as paired epiplastra, entoplastra, hyoplastra, hypoplastra and xiphiplastra (Pritchard & Trebbau, 1984). [10]
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 of Argentina, which dates from 118 to 110 million years ago, [11] [12] and indeterminate remains from the Griman Creek Formation, of New South Wales, Australia, dating to around 100 million years ago. [13] [14]
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 to determine the three long-necked genera ( Chelodina , Chelus , and Hydromedusa ) were each other's closest relatives. [15] This was accepted for some time, but brought into scrutiny, [16] 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. [17] [18] 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, [19] Thomson, 2000. [20] 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: [17]
Taxonomy after TTWG 2021 [21]
Key to Australasian Chelidae |
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1 Forelimbs each with five claws; gular scutes separated by the intergular; intergular scute in broad contact with the anterior margin of the plastron 2 2 Intergular scute not in contact with the pectoral scutes 3 3 Suture between the second and third costal scutes contacting the seventh marginal scute; suture between the third and fourth costal scutes contacting the ninth marginal scute 4 4 Surface of the temporal region covered with distinct regular scales or low tubercles; dorsal surface of the head with a prominent head shield which may be entire or fragmented; cervical scute present or absent 5 5 Precloacal tail length greater than postcloacal length only in adult males; tail round in cross section; cloacal orifice round; tail always shorter than half of carapace length 6 6 Prominent alveolar ridge on the triturating surfaces of the mouth; cervical scute absent (except as a rare variant); no prominent process of the head shield extending down the parietal ridge toward the tympanum Elseya |
Relationships of the living forms based on Georges et al., 2014. [36] [ citation needed ]
Chelidae |
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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.
The eastern long-necked turtle is an east Australian species of snake-necked turtle that inhabits a wide variety of water bodies and is an opportunistic feeder. It is a side-necked turtle (Pleurodira), meaning that it bends its head sideways into its shell rather than pulling it directly back.
Chelodina, collectively known as snake-necked turtles, is a large and diverse genus of long-necked chelid turtles with a complicated nomenclatural history. Although in the past, Macrochelodina and Macrodiremys have been considered separate genera and prior to that all the same, they are now considered subgenera of the Chelodina, further Macrochelodina and Macrodiremys are now known to apply to the same species, hence Chelydera is used for the northern snake-necked turtles.
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 differences between them, although anatomical and largely internal, are nonetheless significant, and the zoogeographic implications of them are substantial. The Pleurodira are known more commonly as the side-necked turtles and the name Pleurodira quite literally translates to side neck, whereas the Cryptodira are known as hidden-necked turtles. The Pleurodira turtles are currently restricted to freshwater habitats in the Southern Hemisphere, largely to Australia, South America, and Africa. Within the Pleurodira, three living families are represented: Chelidae, also known as the Austro-South American side-necked turtles, the Pelomedusidae, also known as the African mud terrapins, and the Podocnemididae, also known as the American side-neck river turtles. However, they were cosmopolitan clade during the Cretaceous and most of the Cenozoic, and even occurred in marine environments around the world.
The Argentine snake-necked turtle, also known commonly as the South American snake-necked turtle is a species of turtle in the family Chelidae. The species is known for the long neck to which its common names refer. Despite appearances, the Argentine snake-necked turtle is probably more closely related to the mata mata than to the Australian snake-necked turtles in the genus Chelodina. H. tectifera is found in northern Argentina, Uruguay, Paraguay, and southern Brazil. Not much is known about it, as it has not been extensively researched. It is a popular pet in the exotic pet trade.
The Namoi River snapping turtle, also commonly known as Bell's turtle, the Namoi River elseya, or Bell's saw-shelled turtle, is a species of turtle in the family Chelidae. The species is endemic to New South Wales, Australia.
Elseya is a genus of large side-necked turtles, commonly known as Australian snapping turtles, in the family Chelidae. Species in the genus Elseya are found in river systems in northern and northeastern Australia and throughout the river systems of New Guinea. They are identified by the presence of alveolar ridges on the triturating surfaces of the mouth and the presence of a complex bridge strut.
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. They can grow quite large, 30 cm or more is not unusual and have a life span of around 20–30 years. They generally do not hibernate as their warmer climate lets them remain active all year round; they also spend more time in the water than other varieties. They are considered omnivore but rely on a constant supply of meat to remain healthy, feeding on basically anything that will fit into their mouth.
Hydromedusa is a turtle genus in the family Chelidae, commonly known as the South American snake-necked turtles. They are quite closely related to the South American side-necked swamp turtles (Acanthochelys) and the snake-necked turtles of the Australian-Melanesian region (Chelodina), but less closely to the spine-necked river turtles of South America (Podocnemididae) which belong to a more modern lineage of Pleurodira.
The Fitzroy River turtle is a species of freshwater turtle in the family Chelidae. It is the only surviving member of the genus Rheodytes, the other member being the extinct form Rheodytes devisi. The species is endemic to south eastern Queensland, Australia and only found in tributaries of the Fitzroy River.
Elseya uberrima is a Pliocene species of extinct Australian snapping turtle.
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, which is formed from the Aboriginal word myuna meaning clear water and the Greek chelys meaning turtle. They have a short neck and the intergular scute completely separates the gular scutes. They have no alveolar ridge separating them from the snapping turtles of the genus Elseya.
Chelodina canni, also known commonly as Cann's snake-necked turtle, is a species of turtle in the family Chelidae. The species is endemic to Australia, where it is found in the northern and northeastern parts of the continent. It has a narrow zone of hybridization with its related species the eastern snake-necked turtle, C. longicollis. For many years C. canni was assumed to be the same species as C. novaeguineae from New Guinea. However, in 2002 it was shown that these two species differ both morphologically and genetically, and therefore C. canni was separated and described as a unique species.
The Gulf snapping turtle or Lavaracks' turtle is a large species of freshwater turtle in the sidenecked family Chelidae. The species is endemic to northern Australia in northwest Queensland and northeast Northern Territory. The species, similar to other members of the Australian snapping turtles in genus Elseya, only comes ashore to lay eggs and bask. The Gulf snapping turtle is a herbivore and primarily consumes Pandanus and figs.
Chelodina (Chelydera) burrungandjii, the sandstone snake-necked turtle or Arnhem Land long-necked turtle, is a medium-sized turtle reaching carapace lengths of 316 mm. The species is found in the sandstone plateaus and escarpments and the plunge pools of Arnhem Land of the Northern Territory. The species had been long recognised as valid. However, it had been difficult to research due to the remoteness of its habitat. Efforts to breed this species in captivity had been largely unsuccessful, until National Aquarium Herpetologist Matthew Benedict lead a successful breeding project in 2021. The species occurs in proximity to Chelodina rugosa, to which it is closely related. For the most part the two species are parapatric in distribution. However, they do come together in limited locations such as plunge pools at the base of the escarpments. In these areas there is hybridization between the species.
Prochelidella is an extinct genus of Early to Late Cretaceous chelid turtles from the Bajo Barreal, Candeleros, Cerro Barcino and Portezuelo Formations of the Cañadón Asfalto, Golfo San Jorge and Neuquén Basins in Patagonia, Argentina. It includes the following species:
Chelodina alanrixi is a species of snake-necked fossil turtle which was described in 2001 using material gathered in Redbank Plains, Queensland, Australia. It is a member of the Chelidae Pleurodira. The fossil has been dated to the Eocene Epoch.
Yaminuechelys is an extinct genus of chelid turtle from Argentina and the Dorotea Formation of Chile. The genus first appeared during the Late Cretaceous and became extinct during the Late Paleocene.
Lomalatachelys neuquina is an extinct genus and species of chelid turtle from Argentina. The specimen was found in the Loma de La Lata zone approximately 75 km from Neuquen City in north west Patagonia, Argentina.
Elseya rhodini, the southern New Guinea stream turtle, is a recently described aquatic species of chelid turtle found south of the central ranges of New Guinea. It inhabits small streams that flow into the major river drainage's south of the ranges.
Scott A. Thomson is an Australian herpetologist, paleontologist, and taxonomist, specialising in turtles of the family Chelidae.