58 million years ago, mammals already lived in the marine environment.

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Until now, paleontologists believed that the most recent evidence of mammals in marine environments such as coasts, deltas, and coastlines dates back to the Eocene, between 48 and 37 million years ago. But recently, a team of researchers discovered mammalian footprints in an ancient delta in southern Wyoming dating back to the late Paleocene, or 58 million years ago.

A large set of fossilized footprints show that large prehistoric mammals were gathering by the sea millions of years earlier than we thought. Anton Wroblewski of the University of Utah and Bonnie Goulas-Wroblewski of the Texas A&M Natural Resources Institute photographed and studied the site of the footprint, which Wroblewski first stumbled upon in 2019 while mapping formed rocks on an ancient coast that is now in Wyoming. .

58 million year old mammal footprints

Plant fossils in the layers above where the tracks were found indicate that the tracks are about 58 million years old, making them the first direct evidence of mammals roaming the marine environment. For example, the first evidence of whales comes from rocks formed 9.4 million years later.

Photographs of footprints of various mammals found in southern Wyoming, along with their images. © Anton F.-J. Wroblewski and Bonnie E. Goulas-Wroblewski

Fossilized mammalian footprints that are 58 million years old or earlier are very rare: the new discovery is only the fourth place in the world where such footprints have been found, and the first where footprints have been found near an ancient coastline. ” There are dozens of tracks in other parts of the trail. There are actually thousands of footprints on this one, so it provides very important information about how these animals moved, what they did, etc. Wroblewski says.

The traces left, in particular, Coryphodon

The researchers recorded footprints in four sediment layers, each representing a different time the footprints were left in the environment. At that time, this region was a coastal delta. ” We do not know how much time these layers represent, but it is almost certainly thousands or even tens of thousands of years. Wroblewski says.

So, these four layers of rock tell us that these animals have appeared more than once in the marine environment. They have done this many times over tens of thousands of years. And that’s why we think it was one of their habits – they did it on a regular basis. “.

Photos of four fingerprints belonging to coryphodon. © Anton F.-J. Wroblewski and Bonnie E. Goulas-Wroblewski

At least two animal species are the source of the footprints. Although the four-toed footprints cannot be associated with any known animal that existed at the time, the five-toed footprints were probably left coryphodonan animal that looks like a hippopotamus.

In a sense, this is a continuation of the temporary existence of Coryphodon. Observing this ecological association means that it will be possible to look for other areas where these environments have survived to see if traces can be found there. concludes George Engelmann of the University of Nebraska at Omaha.

Source: Scientific reports.

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