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‘Enigmatic’ footprints reveal prehistoric crocodile that walked on two legs

This illustration depicts what the prehistoric two-legged crocodile might have looked like.
This illustration depicts what the prehistoric two-legged crocodile might have looked like. (Anthony Romilio/The University of Queensland)

(CNN) -- Ancient footprints embedded in rock in South Korea likely belonged to a prehistoric crocodile that walked on two legs, paleontologists said.

It's the first time this gait has been found in this family of ancient crocs, which typically walked on four legs like modern-day crocodiles and alligators. The well-preserved tracks included footprints that were 18 centimeters (7 inches) to 24 centimeters (9 inches) in length, indicating a body length of up to 3 meters (10 feet.)

"The narrow trackways were made entirely by the back limbs, with clear heel to toe impressions and skin traces in some areas," according to a release about the study, which published Thursday in the journal Scientific Reports.

Similar "enigmatic" footprints found at other sites in South Korea had been thought to belong to giant pterosaurs — prehistoric flying reptiles — walking on two legs.

But the researchers from South Korea and the United States said they likely belonged to the ancient croc, which they named Batrachopus grandis, and their discovery supported the prevailing view among paleontologists that pterosaurs walked on four feet.

Batrachopus grandis would have lived more than 100 million years ago in the early Cretaceous period, predominantly on land rather than water like its counterparts today. It's possible the animal primarily walked on two legs but was also able to walk on four.

No two-legged prehistoric crocodiles had been found from this period, although the study said that crocs that walked on two legs may have roamed the Earth much earlier during the early Mesozoic era that started about 250 million years ago.

The footprints were up to 24 centimeters in length.
The footprints were up to 24 centimeters in length. (Kyung Soo Kim/Chinju National University of Education)

Before coming to their conclusion, the paleontologists debated whether the prints from the forelimbs of these crocs did not penetrate the ground as deeply as the back feet or that the creature was swimming while it made the tracks.

"We ruled out swimming because the trackways are so regular," said Martin Lockley, a paleontologist and professor at the University of Colorado and an author of the study.

"Modern crocs sometimes use hind feet to punt along, but the tracks are irregular incomplete, washed out splayed and not in a regular one foot in front of the next trackway pattern."

They said the consistent absence of forelimb prints and the narrow trackway pointed to a new species that walked on two legs.