You are in the forests of South America, 179 million years ago.

The humid, fern-covered landscape of Middle Jurassic Argentina was quiet, perhaps too quiet. You were crouching behind the massive trunk of a cycad to rest, documenting a herd of Patagosaurus grazing in the distance, when the silence broke.

A sudden, sharp cry—unlike the deep bellows of the sauropods—caused you to freeze. Thirty yards away, the ferns parted, and a Piatnitzkysaurus emerged. It was smaller than you expected, likely under 15 feet long, but its predatory form was terrifyingly efficient.

The theropod wasn't looking at me; it hasn’t spotted you yet. Its head, featuring a pair of distinct crests, tilted sharply as it observed the herd of Patagosaurus. The Piatnitzkysaurus was a bipedal carnivore with long, powerful legs, hinting at high speed. Its arms, proportionately longer than those of later tyrannosaurs, flexed as it shifted its weight, ready to hunt…