One hundred sixty million years ago, an elegant sea monster lay down on its right side and died on the warm, muddy ocean bottom near the present-day town of Lookout, Wyoming. As the creature’s 14-foot-long body was convulsed by one last set of involuntary muscle contractions, its powerful sharklike tail twitched and stirred the bottom mud. A faint trail of bubbles escaped from the corner of its mouth and rose 300 feet to the surface, where tropical sunshine was playing on the waves. Then a bottom current gave the beast a decent burial under a blanket of pale green sand, part of the accumulating sediment layers that would become known as the Redwater Shale Member of the Sundance Formation.
Usually the events leading up to any one individual death in geologic time are obscured, the details lost, the exact time of day not recorded by any sign preserved in the rock record. But from what I know about that ancient Wyoming seabed, I have a mental picture of this one animal in its last hours in the Sundance Sea.
The sea monster was Baptanodon, the fastest, most advanced species among the ichthyosaurs, the fish-lizards, seagoing reptiles with large porpoise-shaped bodies and long, narrow snouts. Baptanodons hunted at dusk. Their eyeballs, as big across as dinner plates, could gather up even the faintest light coming into the upper layer of the water. In my mind, I see my fleshed-out Sundance fossil swimming along in a pod of five or ten individuals, cruising silently 50 feet below the surface, scanning the moonlit water above for prey. The leader of the pod catches the telltale speckled light of armored squid, moving in an immense shoal a thousand strong. The squid rise near the surface every evening at this time to feed on small crustaceans and fish larvae.
Armored squid have big eyes, too--for catching their prey and for detecting their predators. But the baptanodons start their attack from the squid’s blind quarter, behind and below the shoal. Baptanodons also have the deadly advantage of slashing speed. Their bodies have the 40-knot shape preferred by evolution for all its fastest-swimming creations. Mako sharks and albacore, the speediest fishes today, have the same proportions: a teardrop torso, six times longer than it is thick; short, triangular forefins for steering; reduced hind fins; a narrow tail base; and a deep, graceful, crescent-shaped tail fin.
A burst of muscular tail twitches sends the attacking baptanodons up and forward into the shoal’s rear echelons. Squid break formation in every direction. Clouds of camouflaging ink squirt out and swirl in the Sundance water column.
