The ancient oceans were home to the Archelon, a colossal sea turtle that navigated the waters when dinosaurs still roamed the Earth. Its immense size made it a prominent figure in prehistoric marine life. Like many species of its era, the Archelon eventually vanished from the planet’s seas, marking the end of its existence.
The Ancient Archelon
The Archelon was gigantic, reaching lengths of up to 15 feet (4.6 meters) and weighing over 4,000 pounds (2.2 to 3.2 tons). Unlike most modern turtles, its shell was leathery with distinct ridges, not hard and bony. This massive reptile possessed a powerful, hooked beak and strong flippers, well-suited for propulsion through water.
This ancient sea turtle inhabited the warm, shallow waters of the Western Interior Seaway, an inland sea that once bisected North America during the Late Cretaceous period. Its diet primarily consisted of soft-bodied marine organisms such as jellyfish and squid, along with mollusks and crustaceans. Although it shared resemblances with modern leatherback sea turtles, Archelon belonged to a separate evolutionary lineage.
The End of an Era: Archelon’s Extinction
The Archelon became extinct approximately 66 million years ago, coinciding with the Cretaceous-Paleogene (K-Pg) extinction event. While this event is associated with an asteroid impact that devastated dinosaur populations, Archelon’s disappearance involved multiple environmental factors. Its extinction was likely due to a combination of pressures, not a single cause.
Changes in sea levels, including the shrinking of the Western Interior Seaway, limited its habitat. Shifts in ocean currents and a cooling climate also contributed to its decline. These environmental alterations impacted food source availability, as disruptions in the marine food web, such as a decline in plankton-eating fish, affected larger predators. Increased predation on Archelon eggs and hatchlings by newly evolving marine or mammalian species added pressure. The emergence of other large marine turtles, like the dermochelyids, also introduced competition, straining the Archelon’s ability to thrive.
Unearthing the Past: Fossil Evidence
Paleontologists have pieced together Archelon’s history and extinction primarily through its fossilized remains. Many significant Archelon fossils have been unearthed in the Western Interior Seaway region, particularly in South Dakota, Kansas, and North Dakota. The first specimen was named in 1896 by American paleontologist George Reber Wieland, based on a skeleton found in South Dakota.
The fossil record provides invaluable insights into the Archelon’s physical characteristics and the timeline of its disappearance. Scientists analyze the geological layers where fossils are found, noting the presence or absence of Archelon remains in specific strata. A sudden decrease or complete absence of fossils in younger rock layers indicates extinction. Radiometric dating techniques applied to these formations help pinpoint the age of these layers, allowing researchers to accurately determine when the Archelon ceased to exist.