Archelon (Wikimedia Commons).


Archelon (Greek for "ruling turtle"); pronounced ARE-kell-on


Oceans of North America

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About 12 feet long and two tons


Squids and jellyfish

Distinguishing Characteristics:

Leathery shell; wide, paddlelike legs


About Archelon

Dinosaurs weren't the only animals that grew to jumbo sizes during the late Cretaceous period. At a whopping 12 feet long and two tons, Archelon was the one of the largest prehistoric turtles that ever lived (it used to be on top of the charts, until the discovery of the truly stupendous Stupendemys of South Amrica), about the size (and shape, and weight) of a classic Volkswagen Beetle. By comparison with this North American behemoth, the largest Galapagos tortoises alive today weigh a little over a quarter of a ton and measure about four feet long! (The closest living relative of Archelon, the Leatherback, comes much closer in size, some adults of this seagoing turtle weighing close to 1,000 pounds.)

Archelon differed significantly from modern turtles in two ways. First, its shell wasn't hard, but leathery in texture, and supported by an elaborate skeletal framework underneath; and second, this turtle possessed unusually wide, flipperlike arms and legs, with which it propelled itself through the shallow Western Interior Sea that covered much of North America about 75 million years ago.  Like modern turtles, Archelon had a human-like life span--one specimen on display in Vienna is thought to have lived for over 100 years, and probably would have survived much longer if it hadn't asphyxiated on the sea floor--as well as a nasty bite, which would have come in handy when tussling with the giant squids that constituted the bulk of its diet.

Why did Archelon grow to such an enormous size? Well, at the time this prehistoric turtle lived, the Western Interior Sea was well-stocked with the vicious marine reptiles known as mosasaurs (a good example being the contemporary Tylosaurus), some of which measured over 20 feet long and weighed four or five tons. Clearly, a speedy, two-ton marine turtle would have been a less appetizing prospect to hungry predators than smaller, more pliable fish and squids, though it's not inconceivable that Archelon occasionally found itself on the wrong side of the food chain (if not by a hungry mosasaur, then perhaps by a plus-sized prehistoric shark like Cretoxyrhina).