You are in the coastal prairies of South America, 72 million years ago.

The humid air of the Late Cretaceous in southern Chile was thick with the scent of wet ferns. You crouched behind a cycad, checking your camera settings, when a strange, rustling sound made you freeze. It wasn’t a large sauropod; it was lower, more deliberate.

The damp ferns of late Cretaceous Chile parted, revealing not a massive tank, but a compact, armored surprise: a Stegouros. It was roughly the size of a large dog, covered in pebbled armor, but its most striking feature was the tail—a surprisingly flattened structure resembling a fern frond, studded with bone.

You froze as it noticed you. It didn’t run. Instead, the creature immediately pivoted its rear toward you, planting its feet into the mud. It swung that unique, blade-covered tail back and forth with surprising speed, a clear "keep back" warning…