- Archelon ischyros
- 2,200 kilogram(s)
- United States ()
The largest species of sea turtle ever known to have existed was Archelon ischyros, which lived some 80–70 million years ago during the late Cretaceous Period in the seas around what is now North America. The largest specimen on record measured over 4 m long, was approximately 4.9 m wide from flipper to flipper, and is estimated to have weighed more than 2,200 kg. In comparison, the largest species known to exist today, the leathery (leatherback) turtle Dermochelys coriacea, attains a maximum recorded length of 2.91 m, but averages only 1.83–2.13 m, and boasts a maximum recorded weight of 961 kg.
Unlike almost all modern-day chelonians, Archelon did not sport a solid shell. Instead, it possessed a skeletal framework that supported a leathery or bony carapace, rather like the leatherback turtle, its closest modern-day relative. The first recorded specimen was obtained in 1895 from the Pierre Shale of South Dakota by Dr. G.R. Wieland, who formally described and named its gigantic species the following year. It was approximately 80 million years old.