Archelon is a genus of extinct sea turtle, the largest that has ever lived.
Archelon did not have a solid shell like most modern turtles, but a skeletal framework supporting a leathery or bony carapace. It had a pointed tail, a thin skull, a relatively narrow, high-vaulted shell, and a strong overbite.  The live weight of an Archelon ischyros was at least 4,900 pounds.
The largest Archelon fossil, found in the Pierre Shale of South Dakota in the 1970s, measures more than 13.5 feet (4 meters) long, and about 16 feet wide from flipper to flipper. It was a seagoing turtle, related to present day Leatherback Sea Turtles. Its fossils date to 70 million years ago in the Cretaceous period, when a shallow sea covered most of central North America. Most of the known remains have been found in South Dakota, Kansas, and Nebraska. Though anatomically similar to the earlier species Protostega gigas, it was much larger.
|Related turtles (Chelonioidea)||
The enormous size of a grown Archelon probably gave it enough protection from being eaten, so the bones could be part of the armor reduced, which facilitated the movement in the water.
They probably had a strong bite and fed on marine mollusks such as squid. The specimen at the Museum of Natural History in Vienna is thought to have lived to be a century old, and may have died while brumating on the ocean floor.
Archelon in The Land Before Time
Several Archelon are seen swimming at the beginning of the first movie. Three Archelon hatchlings are later shown in the pond where Sharptooth ultimately meets his demise. More Archelon are seen in the sequels, including a named individual, Archie. Archelon also appears in The Land Before Time IX: Journey to Big Water.