Free climbers discover remnants of ancient sea turtle stampede in Italy

Rocks have been found to hold many traces of Earth's ancient history, but usually geologists have to seek them out. Every once in a while, however, these imprints of times past are found by unsuspecting visitors. This occurred in 2019, when a group of free climbers exploring the slopes of Monte Conero in Italy came across a large slab of rock covered in imprints reminiscent of a herd of running animals. One of the climbers ended up showing photos of the imprints to a geologist, which resulted in a study of the area. That study is now published in the journal Cretaceous Research.

A frozen moment in time

After seeing the photos, some of the study authors went back to the site to take additional photographs and rock samples. The site contained more than 1,000 fossilized paddle-shaped footprints on a 200 square meter slab of limestone that was once part of the ancient sea floor.

To get a better idea of the time frame they were looking at, the team conducted stratigraphic logging, thin-section microscopy and microfossil analysis to date and characterize the sediments, along with magnetostratigraphy—a study of magnetic properties in the rocks—to correlate the layer with global geologic time.

They determined the footprint layer to be from the lower Campanian stage of the Cretaceous period, which occurred about 83–80 million years ago. The researchers say this time period is associated with increased seismic activity and climate change. They also posit that the footprints were immediately preserved due to sediment flow (fluxoturbidite) over the area from an earthquake.

"The footprints probably represent a stampede of panicking sea turtles that were mobilized en masse by an earthquake. These tracks were covered by a fluxoturbidite triggered by the same earthquake," the study authors write.

Plesiosaurs, mosasaurs or sea turtles?

The researchers did not immediately know for certain that the prints were those of sea turtles, as no fossils of sea turtles had been previously found in the region. However, there were only a few possibilities, and there was certainly evidence of reptiles living in that time period.

"Excluding fish, which do not use their fins to paddle on the seafloor, for our lowermost Campanian case of Monte Conero, we have to consider marine reptiles of three kinds: plesiosaurs (giant reptiles typically with a long neck and a small head), mosasaurs (i.e., large marine reptiles first found near the Meuse River, and sea turtles, specifically Protostegidae," the study authors explain.

While plesiosaurs, mosasaurs and sea turtles were all capable of creating paddle-like prints, the team says that both plesiosaurs and mosasaurs were more solitary. And although sea turtles are often solitary, some species are known to come together into large groups at certain times, such as during egg-laying.

Even though the identification of the stampeding sea creatures is somewhat uncertain, the team believes that they were most likely sea turtles, and that the scene left behind offers a rare glimpse into their frightened surge toward the deep sea. Perhaps someone will one day stumble upon fossils that will further clarify the identity of the trackmakers.

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