This may be the reason that the marine turtles survived the K/T. Even if all adults (usually foraging in coastal waters) got wiped out, there is usually about five years' worth of juveniles out to sea (sort of like a big aquatic seed bank), waiting to grow up and come to shore. If the pelagic systems were less affected by the extinctions than the coastal systems this may explain way the turtles, alone of all marine reptiles, were able to survive the boundary.