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Here’s what you’ll learn when you read this story:
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Strange footprints on a bed of limestone were discovered by climbers who took photographs to be investigated by paleontologists.
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When paleontologists figured out what the tracks probably meant, they captured additional images and compared them to extinct and extant marine reptiles.
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It is now believed that the markings were left by a herd of ancient sea turtles that had been spooked by a sudden earthquake.
83 million years ago, the Riviera Conero on Italy’s east coast was a submerged Cretaceous refuge for marine reptiles and fish, including the ancestors of modern sea turtles. But one day, ominous noises below caused them to scatter en masse, and their frantic turnip tracks were frozen in time.
As climbers scaled the steep limestone slopes of Monte Cônero in the spring of 2019, they discovered what appeared to be a run of footprints embedded in the rock face. The tracks looked similar to ichnofossils—signs left behind by life forms, but not the remains of the life forms themselves—on a nearby slab of rock discovered by paleontologist Luca Natali a few months earlier. Natali later attributed the tracks to the extinct marine reptile Coneroichnus marinus, considered to be a type of pliosaur.
When the climbers brought digital photos of their discovery to paleontologist Alessandro Montanari of the Geological Observatory of Coldigioco, he knew the prints were worth pursuing. The sheer rock where the footprints lie above La Vela Beach is more than 328 feet (100 meters) above sea level, but that didn’t stop Montanari and his research team. They managed to gain access to the Cônero Regional Park (closed to the public due to rockfall) to survey the area on foot and sent drones to capture more images with a panoramic view from above.
“We hypothesized that the footprints, which were probably made by a group of medium-sized marine vertebrates paddling southwest on a soft pelagic bottom, were preserved on that silty sediment because they were immediately buried and sealed under a calcilutitic turbidite,” Montanari said in a study recently published in Cretaceous research.
What creature could have left so many of these tracks while swimming? Well, during the Late Cretaceous, the only vertebrates living near the ocean floor were fish and reptiles. While the bones of many marine species have been found preserved in limestone that was once underwater, nothing bearing the imprints of their feet, fins or paddles has ever turned up. Such prints would not have lasted long on the sea floor of flowing sediments – they would have been easily erased by the flow of water or washed away by deep currents.
Because fish don’t paddle across the sand with their fins, Montanari and his team had to consider the types of marine reptiles that existed at the time. They thought it was possible that the tracks came from either mosasaurs, plesiosaurs, or sea turtles from the extinct lineage. Protostegidaaeeven though no fossilized remains of these sea turtles or plesiosaurs have been found in the region. Despite the lack of fossil evidence, researchers continued to investigate each avenue, discarding earlier reports of tracks left by a Triassic notosaurus and a sea turtle that lived in the late Pleistocene.
While ancient sea turtles and plesiosaurs were both solitary creatures, females of most extant sea turtle species will migrate long distances and in herds to lay their eggs on tropical beaches. Plus, the Hawaiian green sea turtle (Chelonia mydas) and the Hawksbill turtle (Eretmochelys imbricata) both are known to inhabit shallow reefs and sometimes swim close to the bottom of the sea and brush the sand with their front flippers. The environments in which these turtles live are similar to what is believed to have been Monte Cônero and La Vela beach tens of millions of years ago.
“The prevalence of sea turtle species in these environments leads us to hypothesize that the countless trace fossils of the La Vela slabs represent a mass movement of very large numbers of these animals,” said Montanari, who believes the ancient creatures were likely foraging when frightened. “A sudden earthquake caused a flight out to sea.”
When the already panicked sea turtles tried to escape, some were so close to the sea floor that they left billows in their wake. The earthquake released calcilutitic fluxoturbidite—coarse deposits mixed with fine-grained sediments that would transform into limestone—that buried and preserved the soft carbonate sediment and its record of sea turtle mass exodus. Earthquake activity at this time coincides with the period of climate change known as the Early Campanian Event, which was thought to have been triggered by an asteroid impact.
For any climber who might explore places known to be fossil beds, it might be worth keeping some form of camera handy. It could lead to the discovery of something that has been waiting to be found for tens or even hundreds of millions of years.
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