Some 80 million years ago, an earthquake seemed to have sent a flock of frightened sea turtles scrambling across the seafloor.
Traces of this prehistoric panic were stumbled upon by a group of free climbers in 2019 on a steep slope overlooking the Adriatic Sea, which the public is typically prohibited from accessing due to rockfalls. They noticed a chunk of rock covered with marks that looked like footprints and snapped some photos. One of the climbers later showed these to Paolo Sandroni, a geologist (and fellow free climber) at the Marche region’s Multi-Risk Functional Center in Italy.
Sandroni and his colleague surveyed the site on foot and with drones and found more than 1,000 fossilized, paddle-shaped footprints impressed in limestone, including some rock that had tumbled down to the beach below. This limestone formed from sediment that previously sat on a shallow sea floor. The researchers dated these footprints to the Cretaceous period, around 83 to 80 million years ago—at the time, abrupt climate change, possibly caused by an asteroid strike, ramped up seismic activity.
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“The footprints probably represent a stampede of panicking sea turtles that were mobilized en masse by an earthquake,” Sandroni and his co-authors wrote in a study published in the journal Cretaceous Research.
Fossil footprints from the seafloor are scarce because they’re rarely preserved, but the team thinks these were quickly frozen in time thanks to a blanket of sediment knocked around by an earthquake.
As for the owners of these mysterious ancient flippers, the researchers noted that the only vertebrates that hung out in the deep sea at the time were fish and reptiles. They narrowed down the suspects to huge, extinct marine reptiles called mosasaurs and plesiosaurs or to sea turtles. But these large beasts did not tend to be as social as sea turtles, who migrate in packs to lay eggs, so sea turtles seemed to be the more likely culprit.
Not everyone is convinced of their provenance. These marks don’t “show the spacing, rhythm or anatomy expected from sea turtle flipper strokes,” Anthony Romilio, a paleontologist at the University of Queensland in Australia, told New Scientist. “I am of the opinion they are not of biological origin, but are instead abiotic structures.”
While a terrified turtle rush may be the most enchanting explanation, the team wants to collaborate with researchers who specialize in trace fossils to learn more about these puzzling prints. 
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Lead image: Claudio Giovenzana / Wikimedia Commons
