You are in the oceans of North America, 210 million years ago.

You hung suspended in the deep blue of the Panthalassa Ocean, near what is now British Columbia. The silence was profound, broken only by your own breathing. Then, the light changed.

A shadow, larger than any modern whale, materialized from the gloom. It was a Shastasaurus, and it was over 60 feet long, the longest aquatic creature you have seen so far.

Its body was impossibly slender, tapering toward a small, snoutless head that seemed disproportionate to its immense bulk. It didn't swim aggressively; it glided. Its vast, dark eye passed within a few meters of you, yet it seemed to look right through you, focused entirely on a school of cephalopods. Its mouth opened—toothless, wide—and you felt the sudden, massive displacement of water as it used suction to feed, a silent, efficient behemoth of the late Triassic. It was a terrifying, beautiful display of specialized power.