Species of turtle
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The chicken turtle (Deirochelys reticularia) is a turtle native to the southeastern United States. It is the only extant member of the genus "Deirochelys" and is a member of the freshwater marsh turtle family Emydidae. The chicken turtle's scientific name refers to its extremely long neck and distinctive net-like pattern on its upper shell. There are three regionally distinct subspecies (eastern, western and Florida), which are thought to have evolved when populations became separated during periods of glaciation. These subspecies can be distinguished by their appearance; the western chicken turtle displays dark markings along the seams of its plastron (lower shell), while the plastron of the Florida subspecies is a bright yellow or orange color. Fossil records show that the chicken turtle has been present in the region for up to five million years.
Chicken turtles inhabit shallow, still or slow-moving bodies of water with plenty of vegetation and a muddy substrate. They are not found in rivers or deeper lakes that may be home to predators such as alligators and large fish. The chicken turtle is predominantly carnivorous and feeds mostly on invertebrates such as crayfish, dragonflies and spiders, but is also known to eat tadpoles, carrion and occasionally plant material. It is an active hunter and its long neck allows it to catch fast-moving prey. Although feeding and mating take place in aquatic environments, the chicken turtle is very well adapted to living on land and may spend more than half the year out of the water. Like many reptiles, it spends much of the day basking in the sun to regulate its body temperature, but unlike most other aquatic turtles, it hibernates over the winter months except in the warmer, southernmost reaches of its range.
The chicken turtle is relatively small compared to other related turtles, with males measuring up to around and females around . It is also one of the world's shortest-lived turtles, reaching a maximum age of 20–24 years. There are thought to be around 100,000 adult chicken turtles in the wild. Although the population as a whole is considered secure, its status in some areas is less certain and several states have listed it as threatened or introduced regulations to manage hunting or taking. The word "chicken" in the turtle's vernacular name is apparently a reference to the taste of its meat, which was once popular in turtle soup and commonly sold in southern markets.
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Taxonomy and evolution.
The species was first described in 1801 independently by two French zoologists: as "Testudo reticularia" by Pierre André Latreille, and as "Testudo reticulata" by François Marie Daudin. Both descriptions were based on drawings and a single specimen collected by Louis Augustin Guillaume Bosc in the vicinity of Charleston, South Carolina some years previously. Subsequent studies placed the chicken turtle into various related genera ("Emys", "Clemmys" and "Terrapene") before Louis Agassiz assigned it to the current genus in 1857. He distinguished "D.reticularia" from other North American members of the family Emydidae by the length of its neck, and from the Australian "Chelodina" by the articulation of the neck vertebrae. In his 1940 comparison of Latreille and Daudin's original descriptions, naturalist Francis Harper determined that Latreille's had been published first, hence the currently accepted specific name.
The chicken turtle is the only extant species in the genus "Deirochelys". Its parent family is Emydidae, the freshwater marsh turtles, which are found on every continent except Australia and Antarctica. The name of the genus is derived from the Ancient Greek words for "neck" ("deirḗ") and "tortoise" ("khélūs"), a reference to the species' particularly long neck. The species name "reticularia" comes from the Latin for "net-like" or "reticulated" ("reticulatus"), probably alluding to the turtle's patterned carapace (top shell).
Subspecies.
There are three distinct subspecies of chicken turtle, as described by Albert Schwartz in 1956 from a study of 325 specimens:
Schwartz considered that "D.r.reticularia" is probably most reminiscent of the ancestors of "Deirochelys", and that the other two subspecies most likely developed from it. The western chicken turtle is the most divergent of the three subspecies, suggesting a longer period of separation, possibly after populations were cut off from one another during a period of glaciation. Similarly, "D.r.chrysea" developed from a later population separation, a common phenomenon on the geographically diverse Florida peninsula. Studies of the chicken turtle's mitochondrial DNA support this theory of earlier divergence of the western subspecies from the two eastern ones. It is thought that the Mississippi River prevents intergradation (the presence of populations sharing characteristics of two subspecies) between "D.r.miaria" and "D.r.reticularia" since the chicken turtle does not generally inhabit rivers or moving water. Intergrades of the eastern and Florida chicken turtles are known, however, with several specimens having been collected in north-central Florida.
Fossil record.
Ancestors of the chicken turtle and related turtles of the genus "Chrysemys" may have been present in North America for up to 40 million years. Writing in 1978, Dale Jackson considered "D.reticularia" to have "one of the most complete evolutionary records of any Recent turtle". Fossils have been found throughout its current range; examples dating from the Pliocene (roughly 5.33 to 2.58 million years ago) to the sub-Recent (prior to the start of the Holocene, or Recent, epoch around 11,700 years ago) have been discovered in Florida, in addition to fossils in Pleistocene deposits in South Carolina. A fossil found in Alachua County, Florida dating from the middle Pliocene was originally thought to belong to "D.reticularia", but was later identified by Jackson as an extinct relative, "D.carri". This species was somewhat larger than its modern relative and its shell roughly twice as thick. Other fossil fragments from the Hemingfordian (20.6 to 16.3 million years ago) are considered to belong to even earlier, more primitive members of the genus.
Description.
The chicken turtle resembles the painted turtle ("Chrysemys picta") and some species of cooter (genus "Pseudemys") in appearance, but has an unusually long neck that is close to the length of its shell. It often also has black blotches on the underside of the bridge (the part of the shell connecting the carapace and plastron), which are not present in these other species. The carapace of the chicken turtle is elongated and pear-shaped, with the rear half noticeably wider than the front. It ranges from dark green to brown in color, and features a distinctive yellowish net-like pattern across its entire upper surface. The scutes of the upper shell have a ridged or wrinkled texture and are rough to the touch. Beneath its shell, the chicken turtle has particularly slender ribs, supposedly developed to accommodate its long, muscular neck. Although the chicken turtle shares morphological features with Blanding's turtle ("Emydoidea blandingii"), such as these elongated ribs and the shape of the skull, DNA analysis has shown they are not closely related.
Descriptions of the chicken turtle disagree on the base color of its skin but it is generally reported to be darker than the carapace, varying from olive to brown to black. One of the distinguishing features of "D.reticularia" is a broad yellow stripe on the forelegs. The skin of the neck and head also has light stripes, although narrower, while the tail and rear legs show vertical yellow markings. The head itself is elongated with a somewhat pointed snout but no other distinguishing features, and the digits of the feet are webbed and tipped with claws.
Compared to other turtles, the chicken turtle is small to medium in size. Adults vary in length from around , with an average length of around . The width of the carapace is roughly 65 percent of its length. Mature chicken turtles exhibit some degree of sexual dimorphism; the females are larger and heavier than males, although the males have longer, thicker tails. Unlike the painted turtle, there is no difference between the sexes in terms of the length of the foreclaws.
Chicken turtle hatchlings measure approximately and weigh around . The shell is much rounder than the adults', and the shell and skin are considerably brighter in color, with a greater number of light stripes. The young of the western chicken turtle hatches with the distinctive dark markings on its plastron already present.
Distribution.
Range.
The chicken turtle is found throughout the southeastern United States; its range extends from the Atlantic coastal plain and states such as North Carolina, South Carolina, Georgia and Florida westward through the Gulf plain towards the Mississippi River. It tends to remain in coastal areas and is largely absent from the Piedmont plateau and more mountainous regions in the north of these states. West of the river, its territory reaches as far north as Missouri and as far west as Oklahoma and central Texas. Across its range, the chicken turtle may inhabit many hundreds or possibly thousands of wetland sites, although populations in any particular location are generally small.
Eastern chicken turtle.
The eastern chicken turtle is the most widespread of the three subspecies, with specimens known from eight states. The main bulk of its territory begins on the eastern banks of the Mississippi River in southeast Louisiana and extends eastward along the coastal plain of the Gulf of Mexico. Apart from the coastal region in the south of the state, it is not present in most of Mississippi, save for a small population in the drainage basin of the Tombigbee River. In Alabama, it is again commonly found throughout the coastal plain in the southern half of the state. It is also present further north in the Ridge and Valley region of the Appalachian mountain range, although less common.
Through Georgia, South Carolina and North Carolina, the eastern chicken turtle is again widely found throughout the coastal regions, although specimens have been recorded further inland in North Carolina. It is abundant in northern Florida, especially in the Panhandle region, where it is the only subspecies present. Its range begins to overlap with the Florida chicken turtle towards the north-central part of the state, with intergrades having been identified in Taylor, Levy, Gilchrist and Clay counties.
The eastern chicken turtle is also present in Virginia, although it is very rare there. A small colony was known to inhabit First Landing State Park in Virginia, but several studies have only managed to locate one adult female and it is thought this population may be extirpated. Around to the west, a small group of around 30 adults is present in Isle of Wight County. Neither of these locations is contiguous with the rest of the turtle's range; it is unclear whether these populations are relics of a native and formerly more widespread group, or whether they were introduced to the area.
Florida chicken turtle.
As its name suggests, the Florida chicken turtle is native to Florida and is only found within the state. It is relatively widespread throughout the central and southern portions of the state, although it is absent from the Florida Keys.
Western chicken turtle.
The western chicken turtle's range is generally restricted to locations west of the Mississippi River, although specimens have been found on the river's eastern banks in northwest Mississippi state. Its range extends from the coastal plain of the Gulf of Mexico in Texas and Louisiana, northward into the south and east of Oklahoma and through Arkansas towards Missouri. It may once have been common in the swampland of Missouri's Bootheel region, but is now only found in a few small groups in the extreme southeast of the state. Its territory is also decreasing in Arkansas; diffuse groups are now found only in the northern reaches of the Gulf coastal plain in the south of the state, as well as some regions of the Arkansas River Valley. The western chicken turtle is reasonably uncommon in Texas but its population there is secure. It inhabits the drainage basins of several rivers in the eastern half of the state, such as the Sabine and the Neches.
Habitat.
Chicken turtles are semiaquatic, equally comfortable in wetland habitats and on land. All three subspecies have similar preferences; they like quiet, still or slow-moving bodies of water such as shallow ponds, oxbow lakes, drainage ditches, borrow pits, marshes, swales, cypress swamps, and Carolina bays. Generally, the chicken turtle prefers water with a maximum depth of around , but it is known to inhabit ponds up to deep. It rarely inhabits moving water such as streams or rivers, but may sometimes colonize quieter rivulets