Evolution and systematics
Fossils of these turtles are identified from the Miocene of Australia and South America. They are most carefully associated to the opposite pleurodiran households: the Pelomedusidae of Africa and the Podocnemididae of South America and Africa. Their subfamilial relationships stay poorly understood. Molecular proof means that the Chelidae could be additional divided into three subfamilies: the Hydromedusinae, containing solely the genus Hydromedusa; the Chelidinae, containing all different South American chelids; and the Chelodininae, containing each the shortand long-neck species of Australia and New Guinea. This taxonomic relationship has but to be recognized when it comes to morphological characters. Genetic and morphological information help the revision of the genus Phrynops, which resulted within the erection of two new genera ( Bufocephala and Ranacephala) and the resurrection of three beforehand acknowledged genera (Mesoclemmys, Batrachemys, and Rhinemys). The standing of a number of morphologically distinct Australian “species” is debated amongst taxonomists as a result of the species are just about indistinguishable utilizing genetic evaluation.
Sideneck turtles are extraordinarily numerous in dimension, form, and coloration. Most species have 4 claws on the hind toes and 5 claws on the forelimbs, zero to six neural bones current, the pleural bones virtually all the time assembly on the midline behind the neurals, mesoplastral bones absent, and the pelvis fused to the plastron. Neck elongation is excessive; in some species the size of the neck might exceed that of the carapace. While the carapace tends to be darkish and cryptic, there are just a few spectacularly coloured chelids which will have vibrant crimson, pink, orange, and yellow on the plastron and/or comfortable components.
With the exception of Batrachemys dahli, the entire South American chelids are discovered east of the Andes and as far south as northern Argentina. The remaining species are present in tropical to temperate areas of Australia and New Guinea. This curious distribution could also be the results of a typical ancestor that dispersed across Antarctica earlier than the southern continents separated and drifted aside. No fossils attributable to this household have been discovered outside the present-day vary.
Primarily aquatic, most species inhabit everlasting freshwater rivers, streams, lakes, and ponds. Some species are present in seasonal wetlands which might be dry for a lot of the 12 months, whereas others develop their vary into flooded forests in the course of the wet season. The New Guinea snakeneck turtle ( Chelodina siebenrocki) might frequent estuaries and coastal waters.
Several species estivate by burying themselves within the mud in periods of maximum drought. Steindachner’s turtle (Chelodina steindachneri), an aquatic species that resides within the deserts of Western Australia, is effectively tailored to the extraordinarily excessive temperatures and desiccating situations prevalent for a lot of the 12 months. This species is resistant to evaporative water loss and shops fluids in accent bladders so as to survive whereas buried for the 12 months or two till the rains return.
Feeding ecology and food regimen
Most species are omnivorous to completely carnivorous; nonetheless, the grownup Elseya dentata could also be fully herbivorous. Many numerous variations for specialised feeding are discovered on this household. The snakeneck turtles of Australia and South America have developed very related modes of prey seize. Both teams have independently developed a protracted neck that's tailored for placing at prey whereas suspended within the water column. The unfavourable stress generated by the speedy enlargement of the mouth and neck pulls the pinnacle towards the prey whereas concurrently pulling the prey merchandise into the turtle’s open jaws. Matamatas lie in wait on the murky backside of their aquatic habitat and use a gape-and-suck technique related to that of the snakeneck turtles to seize their prey. Alternatively, some Australian chelids are specialised for feeding on mollusks. As they age, macrocephalic females of the genus Emydura develop monumental skulls that present the drive required for crushing bigger prey.
Females are typically bigger than males; nonetheless, the reverse is true in Pseudemydura and Elusor. Males of the latter genus possess an especially lengthy tail with a singular bony construction which will play a task in copulation. Breeding has been noticed within the early spring for a lot of species, however could also be year-round within the Tropics. Nests are usually constructed in spring and early summer season; nonetheless, some tropical species nest in the course of the winter as effectively. Clutch dimension ranges from one to 28 and two or extra clutches could also be produced per 12 months. The brittle-shelled eggs could also be elongate or spherical, 1.2–2.four in (3–6 cm) in best diameter. Incubation might final greater than 200 days in species that require a interval of diapause (early developmental arrest) for correct improvement. Quite a lot of nest chambers are constructed. The gibba turtle might lay its elongate eggs in shallow nests beneath vegetation, whereas the western swamp turtle makes use of her forelimbs to dig a chamber, which she then enters to deposit her eggs. Researchers in Australia have found that, whereas fully submerged, the feminine northern snakeneck ( Chelodina rugosa) lays her eggs within the muddy backside of momentary ponds. Development is arrested till the water subsides in the course of the dry season, however resumes in time for incubation to be accomplished earlier than the pond fills once more. Hatchlings might stay within the nest till rain softens the hardened soil plug with which most species seal the nest chamber. In excessive instances emergence might happen practically two years after the eggs have been laid. All species analyzed to this point exhibit genetic intercourse willpower.
Thirteen species are listed as Threatened on the IUCN Red List: six are Vulnerable, 4 Endangered, and three Critically Endangered. Eight species are listed as Lower Risk/Near Threatened. The western swamp turtle ( Pseudemydura umbrina), with identified populations of fewer than 400 people, could also be one of many world’s most endangered turtles. Similarly, Hoge’s sideneck ( Ranacephala hogei) is thought from only a few locales in Brazil, and is assumed to be Critically Endangered. The main risk to most species is habitat destruction or degradation. Many of the threatened species are being bred in captivity, providing hope for future repatriations. However, energetic conservation efforts in nature are missing for many species.