Rock climbers in Italy stumbled across evidence of what appears to be a sea turtle stampede that took place nearly 80 million years ago. Now, new research suggests these ancient marine reptiles were fleeing an earthquake.
The climbers recognized the significance of their find because the grooves in the rock face on Monte Cònero overlooking the Adriatic Sea reminded them of others that had made headlines earlier that year. Those grooves had been found in another part of the same regional park and were attributed to a Cretaceous marine reptile pressing its paddles into the seafloor. They consulted with fellow-climber and geologist, Paolo Sandroni, who got in touch with Alessandro Montanari, director of the Coldigioco Geological Observatory (OGC).
Sandroni and another member of the team climbed back to the area to collect rock samples and document the site using a drone.
Hundreds of these tracks are located on a layer of the Scaglia Rossa limestone in Cònero Regional Park, a formation that has been extensively studied for decades and preserves millions of years of deep sea sedimentation, study co-author Montanari told Live Science.
What is now part of a mountain was once a deep seabed folded over and thrust upward by tectonic forces millions of years ago, he said. Rock samples collected immediately above the tracks and analyzed by the team reveal important clues about the tracks’ location and the story behind them. For example, they suggest the sea turtles lived around 79 million years ago during the Late Cretaceous Period and indicate that the limestone was part of an underwater avalanche of mud triggered by an earthquake.
Abundant seismic activity in this formation is also supported by decades of collective study. Thin sections slides of the rock samples reveal microfossils of organisms that live along the seafloor, suggesting a hundreds-of-meters deep seafloor environment.
Normally, any traces left by animals would be erased by currents at the sea bottom and “worms, clams and [other] benthic organisms,” Montanari said. “They basically garden the seafloor,” he noted. But an earthquake caused an underwater avalanche within minutes of the tracks being made, preserving them, he said.
The only vertebrates big enough to make these tracks in the Late Cretaceous were marine reptiles such as sea turtles, plesiosaurs and mosasaurs. The latter two are believed to have been largely solitary, but, if ancient sea turtle behavior mirrored that of some of today’s species, the researchers said, then it is possible they may have foraged near shore or left the water to lay their eggs. Whatever brought them together, an earthquake caused them all to flee at once, the team suggested in the study, forcing some of the turtles to swim in the water above toward the open sea, and others to scurry away closer to the deeper seafloor. The impending underwater avalanche propelled them even further out of the way.
Michael Benton, professor of vertebrate palaeontology at the University of Bristol in the U.K., who was not involved in the research, said the study clearly shows the geological context, but he questioned which animal made the tracks.
“The tracks are unusual because they seem to show underwater punting, where the two forelimbs enter the sediment together and the animal pushes forward,” he told Live Science. Most vertebrates tend to “walk or swim with the limbs out of sequence” rather than putting two limbs down at the same time, he said. “Marine turtles generally have a very efficient swimming mode,” he said, “a bit like underwater flying, where the front paddles swing round” similar to a figure eight pattern, which doesn’t appear to match the tracks found. He also questions why they wouldn’t simply “leave the sea bed and swim” away.
Montanari said that while the prints would benefit from further research, it is clear, geologically, that there was an underwater avalanche triggered by an earthquake. He said he hopes their work will prompt fossil experts to further study the site.
