Kyung Soo Kim, Chinju National University of Education, Kyungnam, South Korea.
Ancient footprints first thought to belong to a pterosaur may actually have been made by a large bipedal ancestor of crocodiles that lived about 110 to 120 million years ago.
Martin Lockley at the University of Colorado Denver and his colleagues found a set of fossilised footprints near Sacheon City, South Korea. The tracks were more detailed and well-preserved than similar ones discovered in 2012 about 50 kilometres away, which were thought to have been made by a giant flying reptile called a pterosaur.
The newly discovered tracks are 18 to 24 centimetres long, and include detailed skin impressions left by the animal’s heels and toes. Lockley and his team say the size and skin patterns are consistent with those belonging to a large ancestor of modern crocodiles, called a crocodylomorph, that walked on two legs.
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The new findings suggest previously discovered footprints may also have been formed by a crocodylomorph, rather than a pterosaur, says Lockley. This was a surprise, he says. “No one knew that large bipedal crocs existed in the early Cretaceous.”
The team has suggested that these tracks may belong to a new species, which they have named Batrachopus grandis.
“The discovery of the new tracks solved the ‘whodunnit’ mystery,” says Lockley. He says the next step will be to look for more tracks in this region, where the quality of preservations is particularly high.
Michela Johnson at the University of Edinburgh in the UK says the tracks appear to have very distinct, chunky-looking toes, in addition to impressions from crocodile-like scales, both of which are more consistent with crocodylomorph rather than pterosaur origin.
“But modern crocodiles have at least some webbing between toes in their back feet, whereas these tracks don’t appear to have any,” she says, adding that it isn’t clear whether this is related to the different way these ancient crocodiles may have walked compared with their modern counterparts.
Pedro Godoy at Stony Brook University in New York says he agrees that the tracks weren’t made by a pterosaur, but thinks more evidence is needed before the footprints can be definitively assigned to an ancient crocodile, since they are particularly large for a crocodylomorph from the Cretaceous period.
Journal reference: Scientific Reports, DOI: 10.1038/s41598-020-66008-7
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