The wavy lines and squiggles etched into a slab of limestone found near Fossil Butte National Monument are prehistoric fish trails, made by Notogoneus osculus as it fed along a lake bottom, says Emory University paleontologist Anthony Martin.
"This is a fish story, about the one that got away 50 million years ago," Martin says. "And I can tell you that the fish was 18-inches long, based on good evidence."
He led a detailed analysis, published May 5 in PLoS One, that gives new insights into the behavior 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," Martin says. "It's a fleeting glimpse, but it's an important one."
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.
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 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.
|Contact: Beverly Clark|