Lake-bed trails reveal ancient fish used to bottom feed

Washington, May 7 (ANI): An Emory paleontologist has found that trails etched out in lake bed could reveal how ancient fish used to live.

Anthony Martin found that wavy lines and squiggles etched into a slab of limestone near Fossil Butte National Monument are prehistoric fish trails, made by Notogoneus osculus as it fed along a lake bottom.

"This is a fish story, about the one that got away 50 million years ago. And I can tell you that the fish was 18-inches long, based on good evidence," said Martin.

He led a detailed analysis that gives new insights into the behaviour of the extinct N. osculus, and into the ancient ecology of Wyoming's former Fossil Lake.

"We've got a snapshot of N. osculus interacting with the bottom of a lake that disappeared millions of years ago. It's a fleeting glimpse, but it's an important one," said Martin.

Fossil Lake, part of a subtropical landscape in the early Eocene Epoch, is now a sagebrush desert in southwestern Wyoming, located in Fossil Butte National Monument and environs.

The region is famous for an abundance of exquisitely preserved fossils, especially those of freshwater fish.

However, trails left by these fish are relatively rare.

The National Park Service had identified about a dozen of them and asked Martin to investigate.

One of the fish trace fossils especially intrigued Martin-in addition to apparent fin impressions of two wavy lines, it had squiggles suggesting oval shapes.

"The oval impressions stayed roughly in the center of the wavy lines and slightly overlapped one another. I realized that these marks were probably made by the mouth, as the fish fed along the bottom," Martin says.

He then deduced that the trace was likely made by N. osculus - the only species found in the same rock layer whose fossils show a mouth pointing downward.

After digital spatial analysis, they found that there exists a mathematical correlation between the trace impressions and the mouth, tail, pelvic and anal fins of an 18-inch N. osculus.

"This provides the first direct evidence of N. osculus bottom feeding. Not only that, the fish was bottom feeding in the deepest part of the lake. Previous research had suggested that the bottom of the lake had such low levels of oxygen that it was hostile to life. Our analysis indicates that, at least seasonally, some fish were living on the lake bottom," said Martin.

The study has been published in PLoS One. (ANI)