See Ancient Tracks Left by Giant Marine Worms

This image shows massive tracks embedded in a stone deposit located near Navas de Estena, in Ciudad Real, Spain. The marks were let behind by massive ancestors of modern-day marine worms. According to investigators, these animals lived long before the time of the dinosaurs.

At the time when these marks were imprinted on the rock layer, the entire area was a seabed, home to countless species of arthropods, mollusks and bryozoa. The giant marine worms lived about 475 million years ago, during a time called the Ordocician Period.

Some of the ancient worms reached a length of about 3 feet (1 meter), and were up to 6 inches (15 centimeters) in diameter. As they crawled on the soft sediments at the bottom of the sea, they left indentations that later on became preserved as the soft rock hardened.

Now, any visitor to the Cabañeros National Park can see them for themselves, the Universities Space Research Association reports.