When very small dinosaur bones were found in a rock quarry in Germany’s Harz Mountains in 1998, people thought they were from baby dinosaurs.

But paleontologist Martin Sander’s work shows that they were probably full grown! Named Europasaurus, they are the smallest giant dinosaur species ever found.

Growth marks on dinosaur bones are similar to growth rings on trees. The rings are far apart while the animal is young and growing quickly. They form closer together as growth slows.

“It is precisely these tight compressed marks that we have discovered just beneath the surface of the fossil bones,” says Sander. So the Europasaurus fossils in the quarry must have been from full-grown animals.

Why was Europasaurus, which was slightly longer and heavier than a car, so much smaller than its cousins the brachiosaurs, which grew up to 148 feet (45 meters) long and weighed as much as a thousand humans?

Back 150 million years ago, most of Germany was underwater. Scientists think that as water levels rose, land and food there became more and more scarce. Europasaurus was forced to adapt to its shrinking habitat, so it evolved into a smaller animal needing less space and food.

Since 1998, an international team of scientists has excavated, or carefully dug up, more than 1,000 dinosaur fossils in the rock quarry. It is one of the few places in the world where the bones and footprints of dinosaurs have been found together.