"Just how did the ancestors of both land- and sea-dwelling turtles manage to make it through three heinous events in the history of life and still be around today? If you thought I was going to say “burrowing,” you would be right, but it gets more complicated than that. After all, though a few turtles use burrows for estivation and others for homes, most turtles do not live in burrows at all. For example, nobody is suggesting that Cretaceous sea turtles dug out submarine burrows to wait out an upcoming apocalypse. So rather than making homes, turtles have used underground environments in another way to save themselves and future generations: by female turtles burying their eggs".
From: The Evolution Underground by Anthony J. Martin
OTHER RECOMMENDED BOOK:
Voyage of the Turtle: In Pursuit of the Earth's Last Dinosaur by Carl Safina