Archelon

Archelon is an extinct genus of giant marine turtles that lived in Late Cretaceous seas of North America. Its largest known species reached about 4.5 meters in length.

Turtle: Turtles are reptiles distinguished by a bony or cartilaginous shell formed from their ribs and vertebrae. Archelon belonged to this reptile group, though its shell was unusually reduced and open-framed.
Archelon ischyros: Archelon ischyros is the largest and best-known species of the extinct turtle genus Archelon. Its fossils establish the genus's exceptional size and distinctive skeletal form.
Sea turtle locomotion: Sea turtle locomotion is movement through water, driven mainly by coordinated strokes of the front flippers. Archelon's broad forelimbs suggest a powerful form of flipper-driven swimming.
George Reber Wieland: George Reber Wieland was an American paleontologist who studied fossil turtles and named Archelon in 1896. His description established the genus from fossils collected in South Dakota.
Protostegidae: Protostegidae is an extinct family of marine turtles that flourished during the Cretaceous. Archelon is commonly classified within this family of large, open-ocean turtles.
Archelon marshi: Archelon marshi is a species of Archelon named from Late Cretaceous fossils found in North America. It represents another named species within the genus, though its distinction from A. ischyros has been debated.
Hydrodynamics: Hydrodynamics is the study of how fluids move and exert forces on objects. Streamlining and drag shaped the swimming demands on Archelon's large body.
Late Cretaceous: The Late Cretaceous is the final epoch of the Cretaceous Period, spanning approximately 100.5 to 66 million years ago. Archelon lived during this interval, before the end-Cretaceous mass extinction.
Carapace: The carapace is the upper part of a turtle's shell, formed from bone and, in some species, overlying horny scutes. Archelon's carapace was reduced to a framework of bones rather than a solid shell.
South Dakota Archelon fossil: A nearly complete Archelon skeleton discovered in South Dakota is among the most famous fossils of the genus. This specimen preserves much of the animal's skeleton and helped establish its body proportions.

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