Archelon

Archelon (from Greek αρχελών meaning ruler turtle) is a genus of extinct sea turtles, the largest that have ever been documented, and including the second largest turtle species after Stupendemys, Archelon ischyros.

Discovery
The first specimen of Archelon (YPM 3000) was collected from the Campanian-age Pierre Shale of South Dakota (a geological formation dated to 80.5 million years ago[1])by Dr. G.R. Wieland in 1895 and described by him the following year (Wieland, 1896). The largest Archelon fossil, found in the Pierre Shale of South Dakota in the 1970s, measures more than 4 metres (13 ft) long, and about 4.9 metres (16 ft) wide from flipper to flipper. It was a marine turtle, whose closest living relative in the present day is the leatherback sea turtle.[2][3] Archelon lived at a time when a shallow sea covered most of central North America. Most of the known remains have been found in South Dakota and Wyoming. Though anatomically similar to the earlier species Protostega gigas, it was much larger.

Biology
Unlike most modern turtles, Archelon did not have a solid shell, but instead had a skeletal framework supporting a leathery or bony carapace. Other distinguishing features include a pointed tail, a narrow skull, a relatively narrow, high-vaulted shell, and a pronounced overbite.[2] The live weight of an Archelon ischyros is estimated at more than 2,200 kg (4,900 lb). They probably had a very strong bite, and were optimized for feeding on pelagic mollusks such as squid.[5] The specimen exhibited by the Museum of Natural History in Vienna is estimated to have lived to be a century old, and may have died while brumating on the ocean floor.