You are in the floodplains of Russia, 252 million years ago.

The air in the Permian river valley was thick, smelling of sulfur and wet ferns, a stark contrast to the dry, dusty scent of the Inostrancevia that had just stepped into the clearing. You froze behind a thick cycad, your heart hammering against your ribs, watching a monster 11 feet long move with terrifying grace.

It was not a dinosaur, but something far more nightmarish—a "reptilian tiger" with skin like a wrinkled, tough rhinoceros. The creature was an apex predator of its time, a gorgonopsian that walked with its limbs squarely beneath its body, not sprawling like a lizard. It stopped, turning its massive, narrow skull, and you caught the sunlight glinting off the six-inch, saber-like canines protruding from its upper jaw.

It was looking for food, and you knew you wouldn't survive a single bite from those jaws. When it raised its head and emitted a low, rumbling hiss, you held your breath, watching it move quite close to your hiding spot…