Growing more than 10 feet (3 meters) long, Protostega was among the largest turtles to ever live. Unlike most turtles, whose shells are made of expanded and fused bones that form a relatively solid dome, widely spaced bones that looked more like the rafters of a roof held up Protostega's leathery shell. Though the shell design provided less protection, the lighter load combined with powerful, flipper-like front legs made Protostega a strong, inexhaustible swimmer. Females likely migrated hundreds of miles to lay eggs on sandy beaches, much like sea turtles do today.

Movement onshore, however, was difficult. An adult female Protostega may have weighed a ton or more, a hefty load to drag out of the ocean to lay eggs. But