Protostegidae

Protostegidae is a family of extinct marine turtles that lived during the Cretaceous period. The family includes some of the largest sea turtles that ever existed. The largest Archelon had a head long. Like most sea turtles, they had flattened bodies and flippers for front appendages; protostegids had minimal shells like leatherback turtles of modern times.

==Anatomy== thumb|Fossil of Rhinochelys nammourensis from Lebanon|left As some of the first marine turtles, the protostegids set the general body plan for future species of sea turtles. They had a generally depressed turtle body plan, complete with four limbs, a short tail, and a large head at the end of a relatively short neck. Like other sea turtles, they possessed oar-like front appendages especially evolved for swimming in the open ocean. Similar to the still-extant, possibly closely related Dermochelyidae, protostegids possessed extremely reduced carapaces. Some specimens had skeletal protrusions from their ribs almost wrapping around their bodies in place of a complete shell. Like modern sea turtles, protostegids had sharp beaks. One of the defining characteristics of the members of the family was their almost-disproportionately large heads. Specifically, some specimens of Archelon have been found with heads long. In addition, the members of the family had somewhat reduced plastrons, as well.