Fossil footprints reveal ancient crocodile that walked on two legs

The discovery was made in the Jinju Formation in South Korea, in a layer of rock dating back to between 110 and 120 million years ago. There, researchers found a series of footprints each measuring between 18 and 24 cm (7 and 9.4 in) long. At a glance they resembled crocodile feet, with clear heel impressions left by the flat-footed way that crocs walk.

The tracks made by Batrachopus grandis in South Korea

The tracks made by Batrachopus grandis in South Korea.  Dr Seul Mi Bae

But there was a problem – no “hand” prints were found alongside them. The team says that the prints they do have are clear and well-formed, with fine details of toe pads and scales still preserved. That rules out two simple explanations: that the hind feet were stepping into the front footprints, or that the front prints just didn’t fossilize.

On closer inspection, the team noticed a few other weird things that indicated that these tracks weren’t made by any kind of crocodile that we know today.

“Typical crocodiles walk in a squat stance and create trackways that are wide,” says Kyung Soo Kim, lead researcher on the study. ”Oddly, our trackways are very narrow looking – more like a crocodile balancing on a tight-rope. When combined with the lack of any tail-drag marks, it became clear that these creatures were moving bipedally.”

An artist's impression of Batrachopus grandis

An artist’s impression of Batrachopus grandis.  Dr Anthony Romilio

The team named the new creature behind the tracks Batrachopus grandis. That groups them in with the crocodile ancestor Batrachopus, while the grandis refers to the fact that this new animal is six or seven times bigger than others of its type.

Judging by the size of the prints, the team extrapolated the size of Batrachopus grandis. The animal would have had legs about as tall as adult human legs, and walked hunched over. From nose to tail it would have measured about 3 to 4 m (9.8 to 13.1 ft) long.

The research was published in the journal Scientific Reports.

Source: University of Queensland

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