Rocky cliffs run into the Adriatic Sea near Ancona, Italy. There, above the pebbly coast in 2019, rock climbers explored steep slabs of limestone — remnants of an ancient seabed. They found thousands of curious imprints in the rock: moon-shaped marks that appeared in pairs and round divots.
Now, researchers have surveyed the marks and suggest that they may be the traces of an ancient sea turtle stampede from some 80 million years ago.
The limestone slabs are in a “ totally forbidden” part of the park because of the danger of rockfall, said Alessandro Montanari, a geologist at Geological Observatory of Coldigioco. “But these guys went anyway,” he said of the rock climbers.
Paolo Sandroni, a geologist with the regional government, showed Dr. Montanari photos of the impressions and said they looked like weird footprints. Dr. Montanari agreed and wondered what creatures roaming the seas of the Late Cretaceous period could leave such traces.
They figured the imprints were made by fins paddling on the seafloor. That excluded fishes and left three reptilian options: giant mosasaurs, long-necked plesiosaurs and sea turtles.
Mosasaurs and plesiosaurs were most likely solitary predators. But hordes of turtles are known to congregate to lay eggs or to seek food where it is abundant.
Dr. Montanari and his colleagues saw a resemblance to turtle-track fossils reported in another study. And they reasoned that a buoyant turtle moving near the seafloor and skimming the sediment with the tips of its front flippers would leave side-by-side crescent shapes.
The scientists sought clues about the event in the area’s rocks. Where the rocks meet the beach, a cross-section of their layers is exposed. The rock layer above the ancient seafloor was formed by an underwater avalanche of loose sediment. This would have covered the tracks quickly, preserving them. That rush of suspended sediment may have been caused by seismic activity, Dr. Montanari said. The earthquake would have spooked the turtles, prompting them to paddle toward the open ocean, the team suggested in a study published last month in the journal Cretaceous Research.
But Dr. Montanari noted that he and his colleagues were “limited in verifying this hypothesis.” So they would like ichnologists — scientists who study fossil traces of tracks, trails and burrows — to come investigate.
Ichnologists who read the paper said they wanted to see more data before accepting that this ground had indeed been trampled by turtles.
“It’s a good bit of detective work and some deductive reasoning,” said Murray Gingras, a geologist at the University of Alberta, praising the research team’s interpretation of the traces. But, he added, these animals wouldn’t normally be expected to hang out in what then was such deep water.
Other ichnologists’ objections were stronger.
“As somebody who studies trace fossils, I don’t think the basic data are there to evaluate them,” said Spencer Lucas, curator of the New Mexico Museum of Natural History in Albuquerque. Dr. Lucas said that turtles propelling themselves forward would push some sediment outward, making a pile behind the track. But that feature, called an expulsion rim, is missing on the marks. He suspected that the curved cavities could have been made by seismic activity. They are more akin to mud cracks than animal tracks, he said.
Ryan King, a paleontologist at Western Colorado University said it was plausible that the impressions were made by turtles, but he wasn’t convinced. Researchers could analyze the size, spacing and pairing of the tracks to verify that they fit with the body size and motion of turtles.
It wouldn’t necessarily be surprising to find turtle tracks in the ocean, Dr. King said. But the impressions might not have been made all at once or because of seismic activity. They may go in the same direction because the animals had been walking toward food or going with the flow of the current. Depending on the characteristics of the sediment, the tracks could have stuck around for some time before burial, he said.
Also, it’s not clear how turtles would react to an earthquake. “There’s a lot of missing pieces that still need to be looked at,” Dr. King said.
But if this was a stampede prompted by panic over an earthquake and swiftly moving sediment, Dr. Montanari said he saw one happy outcome from the story: The sea turtles got away from whatever seismic threat they faced.
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