Trailing a 50-million-year-old Bottom-feeder
Wavy lines and squiggles etched into a slab of limestone found near Fossil Butte National Monument are prehistoric fish trails made by a bottom-feeding Notogoneus osculus as it prowled the depths of the ancient Fossil Lake.

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

Feeding trail of bottom-feeding fish
Feeding trail of a bottom-feeding fish (Notogoneus osculus)
from The Lost World of Fossil Lake

Martin led a detailed analysis of the into the behavior of the extinct N. osculus and the ecology of the former lake in what is now high desert in southwestern Wyoming.

"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."

The remains of Fossil Lake, part of a subtropical landscape in the early Eocene Epoch, is now located in Fossil Butte National Monument and environs. The region is famous for an abundance of exquisitely preserved fossils, especially those of freshwater fish.

Trails left by these fish, however, are relatively rare. The National Park Service had identified about a dozen of them and asked Martin to investigate. Martin specializes in trace fossils, including tracks, trails, burrows and nests made by animals millions of years ago.

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 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.

Martin brought his detailed notes, photos and sketches of the trace fossil back to Atlanta, where he enlisted the aid of disease ecologist Gonzalo Vazquez-Prokopec and geographer Michael Page, two of his colleagues in Emory's Department of Environmental Studies.

Vazquez-Prokopec, who does digital spatial analyses of geographic patterns of diseases and pathogens, applied similar techniques to the trace fossil data. The results showed 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," Martin says. "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."

sources:  Emory University

The Lost World of Fossil Lake
The Lost World of Fossil Lake
Snapshots from Deep Time
by Lance Grande

A dry patch of high desert today, Fossil Lake is what remains of three huge lakes that spread across what is now Utah, Wyoming, and Colorado some 50 million years ago. The place is rich in fossil remains of subtropical plants and animals remarkably well preserved across eons of time.

This book documents the immense formations which captured in fossilized form a moment in the early Eocene period 55 millions years ago. It was a time when the North America continent was primarily subtropical, warmer and far more humid than today.

The author explains of how the fossil lake system was formed, what flora and fauna thrived and died within it's waters, and how they were preserved for mankind to discover and interpret.

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