''Macrochelys'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of very large freshwater turtles in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 '' Acherontemys ...

, native to the Southeastern and Midwestern United States. Only a single

extant Extant or Least-concern species, least concern 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 * Exta ...

species was recognized until 2014, when a study divided it into two or possibly three species. These turtles are easily recognized by three distinct dorsal ridges with raised spikes.

Extant species

Traditionally, only a single extant species (''M. temminckii'') 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 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 dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared ...

nor

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

'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, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

n. Hutchison (2008) considered the genus ''

Chelydrops ''Chelydrops'' is an extinct genus of Chelydridae from Miocene of North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by t ...

'' 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 usua ...

) of

Nebraska Nebraska ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Ka ...

, 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 preserve ...

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

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

) * †'' Macrochelys schmidti'' (from the Early Middle

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

)

References

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