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Megalochelys

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Megalochelys
Temporal range: Late Miocene–Middle Pleistocene
M. atlas skeleton at the American Museum of Natural History
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Suborder: Cryptodira
Superfamily: Testudinoidea
Family: Testudinidae
Genus: †Megalochelys
Falconer & Cautley, 1837
Type species
Megalochelys atlas
(Falconer and Cautley, 1844)
Species

See text

Synonyms
  • Colossochelys Falconer & Cautley, 1844

Megalochelys ("great turtle") is an extinct genus of tortoises that lived from the Miocene to Pleistocene. They are noted for their giant size, the largest known for any tortoise, with a maximum carapace length of over 2 m (6.5 ft) in M. atlas. The genus ranged from western India and Pakistan to as far east as Sulawesi and Timor in Indonesia, though the island specimens likely represent distinct species.[1]

Description

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One species of Megalochelys, M. atlas, is the largest known tortoise, with shells of 2 m (6 ft 7 in) in length having been reported.[2] Popular weight estimates for this taxon have varied greatly with the highest estimates reaching up to 4,000 kg (8,800 lb) in some instances.[3] However, weights based on volumetric displacement of the skeleton suggest a mass of around 1,000 kg (2,200 lb).[4] M. atlas is thus the largest known tortoise.[2] Some island species were considerably smaller, with the Philippine species Megalochelys sondaari only having a carapace length of 70–90 cm (2 ft 4 in – 2 ft 11 in).[1] The shell of Megalochelys is prominently domed, proportionally wide, with large openings for the limbs[2], and is relatively thin despite its size,[5] though the epiplastron (the frontmost-portion of the lower carapace) was forked and very thick.[6] Such forked epiplastra are found in some living tortoises, where they are used for combat and shoving contests between males.[2] The skull of Megalochelys could grow over 30 cm (0.98 ft) in length, and had a deep nasal region and a deep and rather short snout, similar to living Aldabra giant tortoises.[2]

Taxonomy

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The genus Megalochelys was first named in 1837 Hugh Falconer and Proby Cautley based on remains found in the Sivalik Hills of northern India with species Megalochelys sivalensis.[7] However, later in 1844, Falconer and Cautley decided to rename the species Colossochelys atlas[5] as they considered the original name "not to convey a sufficiently expressive idea of the size".[6] During the late 19th century and much of the 20th century, Megalochelys/Colossochelys was considered synonymous with Testudo,[8] and later Geochelone.[9][10] Today, Colossochelys is regarded as a junior synonym of Megalochelys. The original species name M. sivalensis is regarded as a nomen nudum due to lacking a proper description (though the genus name is valid due to differing ICZN standards on the naming of genera and species) making M. atlas, which was accompanied by a proper description, the valid name for this species,[11] though some authors have argued for the validity of Megalochelys sivalensis.[12]

M. margae fossilized humerus bone from Saribatue, Wallanae river, South Sulawesi

Megalochelys is the original and valid name for what has been called Colossochelys. It contains three named species with several unnamed taxa.[11]

  • Megalochelys atlas Falconer and Cautley, 1844[11] Late Miocene to Early Pleistocene, India (Sivalik Hills), Myanmar, ?Thailand
  • Megalochelys cautleyi Lydekker, 1889[11][13] Late Pliocene to Early Pleistocene, India (Sivalik Hills) probable nomen dubium.[11]
  • Megalochelys margae[11] Early Pleistocene, Sulawesi, Indonesia. Size estimation between 1.4-1.9 m long.[11]
  • Megalochelys sondaari Karl and Staesche, 2007 [11] Early Pleistocene (until 1.7 ma) Luzon, Philippines
  • Megalochelys sp. Middle-Late Pleistocene (about 0.8-0.12 Mya) Timor, Indonesia[1]
  • Megalochelys sp. Early Pleistocene (until 1.2 Mya) Java, Indonesia[1]
  • Megalochelys sp. Early Pleistocene (1.4-1.3 Mya[14]) Flores, Indonesia[1]

Cladistic analysis has suggested that Megalochelys' closest living relative is Centrochelys (the African spurred tortoise), with both also being closely related to Geochelone (the star tortoises).[15]

Extinction

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The genus is suspected to have gone extinct due to the arrival of Homo erectus, due to staggered extinctions on islands coinciding with the arrival of H. erectus in these regions, as well as evidence of exploitation by H. erectus. The genus was largely extinct by the end of the Early Pleistocene, but persisted on Timor into the Middle Pleistocene.[11]

See also

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  • Titanochelon a similarly giant tortoise known from the Miocene-Early Pleistocene of Europe
  • Archelon: A Late Cretaceous marine turtle and the largest turtle yet discovered.
  • Stupendemys: the largest freshwater turtle to have ever lived, comparable in size to Megalochelys atlas

References

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  1. ^ a b c d e Rhodin, Anders; Pritchard, Peter; van Dijk, Peter Paul; Saumure, Raymond; Buhlmann, Kurt; Iverson, John; Mittermeier, Russell, eds. (2015-04-16). "Turtles and Tortoises of the World During the Rise and Global Spread of Humanity: First Checklist and Review of Extinct Pleistocene and Holocene Chelonians". Conservation Biology of Freshwater Turtles and Tortoises. Chelonian Research Monographs. Vol. 5 (First ed.). Chelonian Research Foundation. doi:10.3854/crm.5.000e.fossil.checklist.v1.2015. ISBN 978-0-9653540-9-7.
  2. ^ a b c d e Naish, Darren (2024-01-31). "Megalochelys, Truly a Giant Tortoise". Tetrapod Zoology. Retrieved 2024-05-30.
  3. ^ Orenstein, R. 2001. Survivors in Armor: Turtles, Tortoises, and Terrapins. Key Porter Books Ltd.
  4. ^ Brown, B. 1931. The Largest Known Land Tortoise. Nat. Hist. Vol. 31:184–187.
  5. ^ a b Falconer, H., Cautley, P.T. 1844. Communication on the Colossochelys atlas, A Fossil Tortoise of Enormous Size from the Tertiary Strata of the Siwalk Hills in the North of India. Proc. Zool. Soc. Lond. 12:54–84.
  6. ^ a b Murchison, C.D. 1868. Palaeontological Memoirs and Notes of the late Hugh Falconer: With a Biographical Sketch of the Author Compiled and Edited by Charles Murchison. Rob. Hardwicke, 1868.
  7. ^ Falconer, H., Cautley, P.T. 1837. On Additional Fossil Species of the Order Quadrumana from the Siwalik Hills. J. Asiatic Soc. Bengal. Vol. 6:354–360.
  8. ^ Lydekker, R. 1889. Catalogue of the Fossil Reptilia and Amphibia in the British Museum. Part III. Chelonia. London: Brit. Mus. Nat. Hist. 3:74
  9. ^ Hooijer, D.A. 1971. A Giant Land Tortoise, Geochelone atlas (Falconer and Cautley), from the Pleistocene of Timor. Proc. Koninklijke Nederlandsche Akademie van Wetenschappen, Ser. B. Phys. Sci. 74(5):504–525.
  10. ^ Auffenberg, W. 1974. Checklist of Fossil Land Tortoises (Testudinidae). Bull. FL. State Mus. Biol. Sci. 18:121–251.
  11. ^ a b c d e f g h i Rhodin, A.G.J.; Thomson, S.; Georgalis, G.; Karl, H.-V.; Danilov, I.G.; Takahashi, A.; de la Fuente, M.S.; Bourque, J.R.; Delfino M.; Bour, R.; Iverson, J.B.; Shaffer, H.B.; van Dijk, P.P.; et al. (Turtle Extinctions Working Group) (2015). "Turtles and tortoises of the world during the rise and global spread of humanity: first checklist and review of extinct Pleistocene and Holocene chelonians". Chelonian Research Monographs. 5 (8): 000e.1–66. doi:10.3854/crm.5.000e.fossil.checklist.v1.2015. hdl:11336/62240.
  12. ^ Vlachos, Evangelos (2019-08-30). "On the nomenclature of the largest tortoise that ever lived: Megalochelys sivalensis Falconer & Cautley, 1837 vs. Colossochelys atlas Falconer & Cautley, 1844 (Reptilia, Testudinidae)". The Bulletin of Zoological Nomenclature. 76 (1): 162. doi:10.21805/bzn.v76.a050. ISSN 0007-5167.
  13. ^ Lydekker, R. 1889. Catalogue of the Fossil Reptilia and Amphibia in the British Museum. Part III. Chelonia. London: British Museum of Natural History, 239 pp.
  14. ^ van den Bergh, Gerrit D.; Alloway, Brent V.; Storey, Michael; Setiawan, Ruly; Yurnaldi, Dida; Kurniawan, Iwan; Moore, Mark W.; Jatmiko; Brumm, Adam; Flude, Stephanie; Sutikna, Thomas; Setiyabudi, Erick; Prasetyo, Unggul W.; Puspaningrum, Mika R.; Yoga, Ifan (October 2022). "An integrative geochronological framework for the Pleistocene So'a basin (Flores, Indonesia), and its implications for faunal turnover and hominin arrival". Quaternary Science Reviews. 294: 107721. Bibcode:2022QSRv..29407721V. doi:10.1016/j.quascirev.2022.107721. hdl:10072/418777. S2CID 252290750.
  15. ^ Vlachos, Evangelos; Rabi, Márton (December 2018). "Total evidence analysis and body size evolution of extant and extinct tortoises (Testudines: Cryptodira: Pan-Testudinidae)". Cladistics. 34 (6): 652–683. doi:10.1111/cla.12227. hdl:11336/98248. PMID 34706483. S2CID 90619565.
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