The skeleton of Archelon Ischyros, the biggest turtle that has ever lived

 The skeleton of Archelon Ischyros, the biggest turtle that has ever lived. It measured 15 feet from head to toe and weighed almost 5,000 lbs.

Archelon is an extinct marine turtle from the Late Cretaceous, and is the largest turtle ever to have been documented, with the biggest specimen measuring 

The Black Hills of South Dakota, and is now on display at the National Natural History Museum in Vienna, Austria. (This original specimen is much more complete and better preserved than the type specimen used to define the species.

Archelon Had A leathery carapace instead of the hard shell seen in sea turtles. The carapace may have featured a row of small ridges, each peaking at 2.5 or 5 cm (1 or 2 in) in height. It had an especially hooked beak and its jaws were adept at crushing, so it probably ate hard-shelled crustaceans, mollusks, and possibly even sponges, while slowly moving over the seafloor. 

It also potentially consumed other animals, whilst swimming closer to the surface, like jellyfish, squid, or nautiloids. However, its beak may have been better-adapted for shearing flesh, with fish being another possible prey choice. With its large and strong foreflippers, 

Archelon was likely able to produce powerful strokes necessary for open-ocean travel and, if need be, escape from fellow marine predators. It inhabited the northern Western Interior Seaway, a mild to cool temperate area, dominated by plesiosaurs, hesperornithiform seabirds, and mosasaurs. It may have gone extinct due to the shrinking of the seaway, increased infant mortality rates (in the sea), higher instances of egg and hatchling predation (on land), and a rapidly cooling climate.