You are in the riverbanks of North America, 360 million years ago.

The water in the Devonian estuary was thick, a brown soup of mud and algae that barely let the sunlight penetrate. You were paddling on a canoe silently in a shallow, hidden channel, watching a Stethacanthus patrolling the bottom. The shark was about six feet long, its strange, ironing-board-shaped dorsal fin cutting through the murk, unaware that something much larger was watching.

That “something” was a 12-foot-long Hyneria.

You saw the large, elongated shape of the fish before the shark did—a sudden, subtle displacement of the water near a submerged bank of vegetation. The top predator, with dark stripes over its heavily scaled body, was camouflaged, waiting in the gloom. As the shark drifted closer, perhaps looking for a smaller fish to eat, the Hyneria struck.

It wasn't a slow chase as you noticed. It was an explosive surge of muscle and powerful fins. In a fraction of a second, the water erupted, and the shark abruptly sank and disappears. The next thing you knew, you see the Hyneria submerging from the waters, with the shark clamped firmly in its massive jaws, its two-inch fangs puncturing the shark's cartilage and skin.

The Hyneria didn't waste time. With a violent head shake, it begins to swallow the shark headfirst as it swims alongside you and your canoe, making you hold your breath. The Stethacanthus, despite its own formidable appearance, was just another meal for the apex predator of these Devonian waters.