When the digging machine cut a furrow to plant pines in the arid soil near the medieval town of Cuenca in the 1980s, it sliced through more than 100 million years to one of Europe's richest seams of fossils.
It was a fluke that opened the way to a series of discoveries about the creatures that walked our planet in the Cretaceous period, between 65 and 145 million years ago.
The latest secret: a strange hump-backed dinosaur, fossilised after it had devoured its prey about 125 million years ago.
Six metres (20 feet) long from snout to tail tip, the dinosaur had jaws and small, clawed forelimbs, a curved spine and small hump.
Pepito, as the creature has been nicknamed by the team from Autonomous University of Madrid who dug it out, was a fast and powerful hunter.
And it had apparently eaten recently.
The unique, nearly complete fossil contained the remnants of its prey in the abdominal cavity.
Baptized Concavenator corcovatus (from "Conca", the Latin word for Cuenca; "ven