Megalochelys

Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Cladus: Sarcopterygii
Cladus: Rhipidistia
Cladus: Tetrapodomorpha
Cladus: Eotetrapodiformes
Cladus: Elpistostegalia
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Cladus: Sauria
Cladus: Archelosauria
Division: Pan-Testudines
Division: Testudinata
Ordo: Testudines
Subordo: Cryptodira
Superfamilia: Testudinoidea

Familia: Testudinidae
Genus: †Megalochelys
Species: †M. atlas – †M. cautleyi – †M. margae – †M. sondaari
Name

Megalochelys Falconer & Cautley, 1837: 358
Type species

Megalochelys siwalensis = Megalochelys atlas 1844

Megalochelys atlas

References
Primary references

Falconer, H. & Cautley, P.T. 1837. On additional fossil species of the order Quadrumana from the Sewálík Hills. Journal of the Asiatic Society of Bengal 6: 354–360. BHL Reference page.

Additional references

Turtle Extinctions Working Group (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., and van Dijk, P.P.). 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. Download

Megalochelys ("great turtle") is an extinct genus of cryptodiran tortoises that lived from the Miocene to Pleistocene. They are noted for their giant size, which is among the largest of any known testudine, with a maximum carapace length over 2 m (6.5 ft) in M. atlas. During the dry glacial periods it ranged from western India and Pakistan (possibly even as far west as southern and eastern Europe) to as far east as Sulawesi and Timor in Indonesia, though the island specimens likely represent distinct species.[4]

Description

One species of Megalochelys, M. atlas, is the largest known tortoise, with a shell length over 2 m (6.6 ft), an estimated total length of 2.7 m (8.9 ft), and an approximate total height of 1.8 m (5.9 ft).[5] 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.[6] However, weights based on volumetric displacement of the skeleton,[7] or inferences based on two-dimensional skeletal drawings,[8] indicate that M. atlas was probably closer to 1,000 to 2,000 kg (2,200 to 4,400 lb) in mass. M. atlas is thus the largest known tortoise. The only larger turtles were the marine Archelon and Protostega from the Cretaceous Period, and the aquatic, freshwater Stupendemys of the South American Late Miocene. A similarly gigantic tortoise, Titanochelon, is known from the Miocene to Pleistocene of Europe, which had shell lengths of up to 2 m (6.6 ft).

Like the modern Galápagos tortoise, M. atlas' weight was supported by four elephantine feet. Like other tortoises, it is thought to have been herbivorous.
Taxonomy

Megalochelys is the original and valid name for what has been called Colossochelys. It contains three named species with several unnamed taxa.[1]

Megalochelys atlas Falconer and Cautley, 1844[1][3] Late Miocene to Early Pleistocene, India (Sivalik Hills), Myanmar, ?Thailand
Megalochelys cautleyi Lydekker, 1889[1][9] Late Pliocene to Early Pleistocene, India (Sivalik Hills) probable nomen dubium.[4]
Megalochelys margae[1] Early Pleistocene, Sulawesi, Indonesia
Megalochelys sondaari Karl and Staesche, 2007 [1][10] Early Pleistocene (until 1.7 ma) Luzon, Philippines
Megalochelys sp. Middle-Late Pleistocene (about 0.8-0.12 Mya) Timor, Indonesia[4]
Megalochelys sp. Early Pleistocene (until 1.2 Mya) Java, Indonesia[4]
Megalochelys sp. Early Pleistocene (until 0.9 Mya) Flores, Indonesia[4]

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).[11]
Extinction

The genus is highly 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.[4] The genus was largely extinct by the end of the Early Pleistocene, but persisted on Timor into the Middle Pleistocene.[4]
References

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.
Falconer, H. and Cautley, P.T. 1837. On additional fossil species of the order Quadrumana from the Siwalik Hills. Journal of the Asiatic Society of Bengal 6:354–360.
Falconer, H. and 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. Proceedings of the Zoological Society of London 1844(12):54–84.
Rhodin, Anders; Pritchard, Peter; van Dijk, Peter Paul; Saumure, Raymond; Buhlmann, Kurt; Iverson, John; Mittermeier, Russell, eds. (2015-04-16). 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.
Hirayama R, Sonoda T, Takai M, Htike T, Maung Thein ZM, Takahashi A. 2015. Megalochelys: gigantic tortoise from the Neogene of Myanmar. PeerJ PrePrints 3:e961v1 https://doi.org/10.7287/peerj.preprints.961v1
Orenstein, R. 2001. Survivors in Armor: Turtles, Tortoises, and Terrapins. Key Porter Books Ltd.
Brown, B. 1931. The Largest Known Land Tortoise. Nat. Hist. Vol. 31:184–187.
Paul, G.S., and Leahy, G.D. (1994). Terramegathermy in the time of the titans: Restoring the metabolics of colossal dinosaurs. Paleontol. Soc. Spec. Publ. 7, 177-198
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.
Anders G.J. Rhodin; Scott Thomson; Georgios L. Georgalis; Hans-Volker Karl; Igor G. Danilov; Akio Takahashi; Marcelo S. de la Fuente; Jason R. Bourque; Massimo Delfino; Roger Bour; John B. Iverson; H. Bradley Shaffer; Peter Paul van Dijk (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" (PDF). Chelonian Research Monographs. 5 (8): 000e.1–66. doi:10.3854/crm.5.000e.fossil.checklist.v1.2015.
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.