Turtles vary widely in size, although marine turtles tend to be relatively big animals. The largest chelonian is a marine turtle, the great leatherback sea turtle, which can reach a shell length of 200 cm and can reach a weight of over 900 kg. Freshwater turtles are smaller, with the largest species being the Asian softshell turtle Pelochelys cantorii, which has been reported to measure up to 200 cm (Das, 1991). This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North America, which attains a shell length of up to 80 cm and a weight of about 76 kg. Giant tortoises of the genera Geochelone, Meiolania, and others were relatively widely distributed around the world into prehistoric times, and are known to have existed in North and South America, Australia, and Africa. They became extinct at the same time as the appearance of Man, and it is assumed that humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galapagos Islands and can grow to over 130 cm in length, and weigh about 300 kg .
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm in length and weighs about 140 g. Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South Americ. The shell length of many species in this group is less than 13 cm in length.