Family Protostegidae

The protostegids numbered among their members some of the most spectacular sea turtles that ever lived. All are now extinct, but they thrived during the Late Cretaceous.

By that time, the protostegids had developed the 2 main features that distinguish all sea turtles from their land and river-based relatives. First, since there were fewer predators in the sea, they did not need such heavy armor on their backs, and so the shell was reduced to a much lighter structure, which also made them more maneuverable. Second, the toes of the front and back limbs were greatly elongated, and modified into broad flippers for swimming.

Today, only 7 species of sea turtle survive, grouped in 2 families. All are endangered due to man's interference with their habitats, especially the nesting beaches. The green turtle and the great leatherback turtle, both of warm seas, are the most familiar members. No sea turtle, either extinct or modern, can retract its head or legs into the shell.

name: Archelon time: Late Cretaceous locality: North America (Kansas and South Dakota) size: 12 ft/3.7 m long This giant turtle of the Cretaceous seas did not have the heavy, many-plated shell characteristic of its land and freshwater relatives. Instead, the shell of Archelon was reduced to a framework of transverse struts, made from the bony ribs that grew out from its backbone. Most probably, the ribs were covered by a thick coat of rubbery skin (as seen in the modern leatherback turtle), rather than by the usual plates of horn.

The limbs of this ancient sea turtle were transformed into massive paddles that would have cleaved the water in powerful, vertical strokes — the method is comparable to the underwater flight of penguins, which propel themselves along by flapping their wings. The front flippers of Archelon were well developed, and would have provided the main propulsive force.

Like the modern leatherback turtle, Archelon probably fed on a diet of jellyfish, whose soft bodies were easily dealt with by the reptile's weak jaws and toothless beak.

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