''Macrochelys'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of very large freshwater turtles in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Chelydridae The Chelydridae is a family of turtles that has seven extinct and two extant genera. The extant genera are the snapping turtles, ''Chelydra'' and '' Macrochelys''. Both are endemic to the Western Hemisphere. The extinct genera are '' Acherontemy ...

from Southeastern United States. Only a single

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

species was recognized until a 2014 study divided it into two, or possibly three species.

Extant species

Traditionally, only a single extant species was recognized, but following reviews, two species are now recognized:Reptile Database
Macrochelys.
Retrieved 26 September 2017.

Turtle Taxonomy Working Group The Turtle Taxonomy Working Group (TTWG) is an informal working group of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group (TFTSG). It is composed of a number of leading turtle taxonomists, with varying participation by individual partici ...

hodin, A.G.J., Iverson, J.B., Bour, R. Fritz, U., Georges, A., Shaffer, H.B., and van Dijk, P.P.(2017). "Turtles of the World: Annotated Checklist and Atlas of Taxonomy, Synonymy, Distribution, and Conservation Status (8th Ed.)." In: Rhodin, A.G.J., Iverson, J.B., van Dijk, P.P., Saumure, R.A., Buhlmann, K.A., Pritchard, P.C.H., and Mittermeier, R.A. (Eds.). "Conservation Biology of Freshwater Turtles and Tortoises: A Compilation Project of the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group." ''Chelonian Research Monographs'' 7:1–292. . Anatomical differences between the two species of ''Macrochelys'' include the shape of the caudal notch at the rear of the carapace and the angle of the squamosal bone at the rear of the skull. The two species are estimated to have diverged less than 3.5 million years ago. * ''Macrochelys suwanniensis'' Thomas et al., 2014 – Suwannee snapping turtle * ''Macrochelys temminckii'' ( Troost, 1835) –

alligator snapping turtle The alligator snapping turtle (''Macrochelys temminckii'') is a large species of turtle in the family Chelydridae. The species is native to freshwater habitats in the United States. ''M. temminckii'' is one of the heaviest freshwater turtles in ...

A third species has been proposed,Thomas, T., Granatosky, M. Bourque, J., Krysko, K., Moler, P., Gamble, T., Suarez, E., Leone, E., Enge, K. & Roman, J. (2014). "Taxonomic assessment of Alligator Snapping Turtles (Chelydridae: ''Macrochelys''), with the description of two new species from the southeastern United States." ''Zootaxa'' 3786(2): 141–165. but its validity is disputed.Folt, B.; and C. Guyer (2015). "Evaluating recent taxonomic changes for alligator snapping turtles (Testudines: Chelydridae)." ''Zootaxa'' 3947(3): 447–450. Neither the

Reptile Database The Reptile Database is a scientific database that collects taxonomic information on all living reptile species (i.e. no fossil species such as dinosaurs). The database focuses on species (as opposed to higher ranks such as families) and has entrie ...

nor

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

's Tortoise and Freshwater Turtle Specialist Group recognize it as separate from ''M. temminckii''. * ''Macrochelys apalachicolae'' Thomas et al., 2014 – Apalachicola snapping turtle

Fossil history and extinct species

Unlike the

as a whole, the

''Macrochelys'' is exclusively

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

n. Hutchison (2008) considered the genus '' Chelydrops'' to be a junior synonym of ''Macrochelys'', and recombined its type species, ''Chelydrops stricta'' from the Miocene (Early

Barstovian The Barstovian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 16,300,000 to 13,600,000 years BP, a period of . It is usu ...

) of

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...

, as the (then) fourth species of ''Macrochelys''. There are two other species known only from

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

remains: * †''Macrochelys auffenbergi'' Dobie, 1968 (from the Middle

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...

) * †''Macrochelys schmidti'' (from the Early 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 recen ...

)

References

Chelydridae Reptiles of the United States Extant Burdigalian first appearances Turtle genera Taxa named by John Edward Gray {{Turtle-stub