Archelon was a giant marine turtle that lived roughly 80 to 74 million years ago, in the shallow sea that once covered much of central North America during the Late Cretaceous.
Bigger than any living sea turtle
Archelon could reach around 4 meters (13 ft) from head to tail — noticeably larger than the biggest living sea turtle today, the leatherback, which tops out at around 2 meters. Unlike modern sea turtles, Archelon's shell wasn't a solid, rigid dome — it had a more flexible, leathery covering over a reduced bony framework, likely to save weight.
Living among giants
Archelon shared its ocean, the Western Interior Seaway, with some of the largest marine predators of the Cretaceous, including large mosasaurs. Its size may have been at least partly a defense against being an easy meal for those predators.
A single, well-known specimen
Much of what's known about Archelon comes from a small number of well-preserved fossils, including a famous, nearly complete specimen discovered in South Dakota that remains one of the most important sea turtle fossils ever found.