What is the largest living species of sea turtle by average adult mass?

The leatherback sea turtle is the largest living species of sea turtle by average adult mass. Unlike hard-shelled turtles, it has a flexible, leathery carapace supported by small embedded bones.

Adult leatherbacks commonly weigh several hundred kilograms, and exceptional individuals can be substantially heavier. Their streamlined bodies and powerful flippers allow them to travel across entire ocean basins. They are also capable of diving to great depths while pursuing jellyfish and other soft-bodied prey.

Leatherbacks lack the heavy bony shell characteristic of green, loggerhead, and hawksbill turtles. Their flexible covering helps distinguish them from other living sea turtles and contributes to their ability to withstand pressure during deep dives.

They are widely distributed in tropical and temperate oceans, but nesting females return to sandy beaches. Plastic pollution is a serious hazard because floating bags can resemble jellyfish, their principal food. “Largest” here refers to living species, not the biggest extinct turtle relatives.