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Protostega gigas

Fossil Sea Turtle Skull

Protostega meaning (first roof) is an extinct genus of marine turtle containing a single species, Protostega gigas. Its fossil remains have been found in the Smoky Hill Chalk formation of western Kansas dated to 83.5 million years ago. Fossil specimens of this species were first collected in 1871, and named by Edward Drinker Cope in 1872. With a length of 3 meters (9.8 ft.), it is the second-largest sea turtle that ever lived, second only to the giant Archelon.

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 lay eggs on the beach they did by the dozens, a reproductive strategy of safety in numbers that helped at least a few survive to adulthood. In fact, marine turtles were the only seagoing reptiles to escape extinction at the end of the Cretaceous, 65 million years ago.

A large and pointed head with a sharp beak and strong jaws probably helped the ancient turtles feed on slow-moving marine creatures such as jellyfish and shellfish as well as seaweed and floating carcasses—much as their descendants do today. Shark teeth embedded in Protostega bones housed at a museum in Chicago suggest the turtles were sometimes a meal themselves.

This skull was found in 1945 by George Sternberg in western Kansas. The original skull is in the collections of the Denver Museum of Natural History and is specimen number 1663.