Temporal range: Late Cretaceous
- ARCHELON is also a sea-turtle conservation society, see ARCHELON, the Sea Turtle Protection Society of Greece
The first specimen of Archelon (YPM 3000) was collected from the Pierre Shale of South Dakota 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. Archelon's fossils date to around 75-65 million years ago in the Late Cretaceous period, 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.
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. 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. 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. However, brumation in reptiles is a response to cold weather and it is unlikely that the Western Interior Sea was ever that cold.
Popular culture 
An Archelon made an appearance in the Hammer Film Productions 1966 remake of One Million Years B.C.. Archelon also appeared in the Walking with Dinosaurs spinoff special Sea Monsters, and in Prehistoric. The film The Land Before Time IV: Journey Through the Mists features a helpful, atypically cave-dwelling Archelon named "Archie" assisting the juvenile sauropod named Littlefoot in the story.
- "Archelon". BBC - Science & Nature. Retrieved 2009-05-25.
- Marine Turtles
- BHI/Fossils & Minerals/Rept. and Amph./Archelon
- Hay, O. P. 1908. The fossil turtles of North America. Carnegie Institution of Washington, Publication No. 75, 568 pp, 113 pl.
- Wieland, G. R. 1896. Archelon ischyros: a new gigantic cryptodire testudinate from the Fort Pierre Cretaceous of South Dakota. American Journal of Science, 4th Series 2(12):399-412, pl. v.
- Wieland, G. R. 1902. Notes on the Cretaceous turtles, Toxochelys and Archelon, with a classification of the marine Testudinata. American Journal of Science, Series 4, 14:95-108, 2 text-figs.
- Wieland, G. R. 1906. The osteology of Protostega, Memoirs of the Carnegie Museum, 2(7):279-305.
- Wieland, G. R. 1909. Revision of the Protostegidae. American Journal of Science, Series 4. 27(158):101-130, pls. ii-iv, 12 text-figs.
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