Turtles (Order Testudines or Chelonia) are unique among vertebrates in having a shell that incorporates both dermal armor, vertebrae, and ribs. Other characteristics include a lengthened neck, limb girdles that lie within the ribcage, a keratinous beak instead of teeth, and limbs that retract into the shell (except in marine turtles). There is considerable uncertainty about which reptile group gave rise to them; evidence exists for both the anapsids (the procolophonids and parieasaurs) and the diapsids (lizards and snakes).
The earliest turtles in the Late Triassic 210 million years ago could not withdraw their heads into their shells: in Proganochelys, the head was protected by loose armor plates, in the tortoiselike australochelids the neck was guarded by an extension of the carapace.
There are two major groups of living turtles. The Side-necked turtles (Suborder Pleurodira) are able to fold their necks sideways into their shells, while the Hidden-necked turtles (Suborder Cryptodira) pull their necks straight back between their shoulder blades. Pleurodires, such as the Snake-necks (Chelodina) and the Matamata (Chelus fimbriatus), are only found in South America, Australia, and Africa. The cryptodires include Snapping turtles (Chelydridae), Sea turtles (Chelonioidea), Softshelled turtles (Trionychoidea), and Freshwater terrapins and Land tortoises (Testudinoidea). By the Late Jurassic, sea turtles were common in many areas of Europe and Asia.
The largest living turtle is the Pacific leatherback (Dermochelys coriacea), which is found throughout the Pacific and indian Oceans and averages 6-7 feet from beak to tail. The largest freshwater turtle is the Alligator snapping turtle (Macroclemys temminckii), which has an average length of 15-26 inches and a record length of 31.5 inches; weights upwards of 300 pounds have been recorded. The largest known fossil turtle, Archelon ischyros, measured up to 16 feet long and 12 feet wide and may have weighed as much as 11,000 pounds. It lived some 70 million years ago in marine waters of the Late Cretaceous. its fossils have been found in South Dakota, Kansas, and Colorado.
The Hindu legend of a giant tortoise that supports an elephant on which the earth rests could be based on fossils of the Pliocene Testudo [Colossochelys] atlas, a land tortoise with a carapace 6 feet wide that is known from deposits in northern india and Pakistan. Hugh Falconer and P.T. Cautley, "Conclusion of Paper on Colossochelys atlas," Proceedings of the Zoological Society ofLondon 12 (1844): 84-88.
Of the six turtles in this list, one appears to be an alligator snapper, one is an enormous marine cryptid, one is a land tortoise that may have survived until very recently, one could be a giant softshell or pleurodire, one is probably a known species of softshell, and one is a six-legged anomaly.
Beast of 'Busco; Father-of-All-the-
Turtles; Giant Malagasy Tortoise; HoAn Kiem Turtle; Ndendeki; Pearl Turtle
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