by Whit Gibbons

July 27, 2008

Two questions I was asked recently fit together nicely: What are the largest living turtles? What is the smallest species of turtle in the world?

Although not the largest turtles in the world, several terrestrial and freshwater species from different regions of the world qualify for the Big Turtle Hall of Fame. Confirming the record size for length or weight is difficult because people often estimate, and therefore exaggerate, size instead of using a ruler and scales. Because true measurements have sometimes been difficult to obtain, several species have been declared to be the largest freshwater turtle in the world.

North America's largest freshwater turtle is the alligator snapper. Males commonly reach shell lengths of two feet and weigh close to 100 pounds. However, shell length records of two and a half feet have been verified. The heaviest legitimate weight records are between 200 and 250 pounds, and possibly one of 316 pounds. In South America, an Amazon River turtle known as the arrau, may get even longer than alligator snappers. Big females have an average shell length of more than two feet and a maximum of almost three. Average body weight of these river giants is more than 50 pounds, with the maximum being 160.

Ecological studies on freshwater turtles of Asia are sparse, but some of the softshelled turtles have been reported to reach enormous sizes. Included among them is what sounds like a sure candidate for a horror movie--Bibron's frog-faced giant softshell turtle--at three and a half feet. The Southeast Asian narrow-headed softshell turtle has been reported to reach a shell length of almost four feet. The Shanghai softshell turtle, a very rare species on the verge of extinction, is considered by some turtle biologists to hold the record size for freshwater turtles. Adult females are typically two and a half to four feet long, with one reported record being almost six feet from front to back of the shell. The record weight reported for the species is more than 400 pounds.

The largest living land turtles are the giant tortoises that live on the Galapagos Islands in the Pacific and the Seychelles in the Indian Ocean. (A tortoise, by the way, is a turtle that lives on land.) The straight-line length of their high-domed shells approaches four feet, and individuals often weigh more than 400 pounds.

The largest living turtle of all, both in length and body mass, is indisputably the leatherback sea turtle. These giants are so large that if one were stood on end in a normal room, the head would poke through the ceiling. The record shell length reported for a leatherback was a male that washed ashore in Wales, between the Irish Sea and North Atlantic. The animal weighed more than a ton, and the length down the middle of the leathery shell was eight feet, five inches. When the front flippers were extended, they spanned over seven and half feet. No other living species of turtle comes close to the size of the largest leatherbacks.

Determining the smallest species of turtle is more problematic than stating that the leatherback is the largest turtle in the world. The bog turtle is generally considered to be the smallest species in North America, because the maximum length is under four and a half inches. Most adults are less than four inches long. The females of all other U.S. turtles reach larger sizes than any bog turtles. However, the issue is confounded because adult males of some of the map turtles, such as the Texas map turtle and Cagle's map turtle, are smaller than either sex of adult bog turtles. These miniature turtles normally do not reach a length of four inches.

Despite the small size of even the largest bog turtles, the record for the smallest turtle in the world in body length should probably reside with the speckled padloper tortoise of South Africa. The species holds the uncontested record for being the smallest tortoise in the world, and the maximum length of females, which are slightly larger than males, is less than four inches, thus qualifying the species as the smallest turtle in the world.

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