SOUTHEAST STUDENTS' RESEARCH PROJECT COULD REWRITE THE RECORD ON FOSSILS

Fossil research under way at Southeast Missouri State University could push the timeline for the development of some burrowing marine organisms back hundreds of millions of years.

Tammy L. Eifert of Jackson and Phillip Statler of Patton, both seniors majoring in geoscience, are studying unusually large fossilized animal burrow structures found in Mammoth Cave National Park in Kentucky.

The burrow structures, which measure approximately 1.5 to 2.5 inches in diameter, were found in rock formations dating back to the Mississippian age (approximately 350 million years ago).

Photos from the cave site show the burrow structures look almost like black tubing branching over the floor of the cave.

The burrow structures were exposed, and did not have to be excavated, Eifert, 36, said.

"Some of it actually extends into the rock about three feet," she said. "We've also found some that extend down into the waterfall itself."

In addition to determining where the structures fit in the paleontological timeline, the students are trying to determine what made the burrows.

The rock formation in which the structures were found show the area was "a warm shallow sea" at the time the burrows were formed, Eifert said, which means some type of marine organism -- possibly a worm, or maybe an organism resembling a crab or shrimp -- made the burrows.

"They were literally mining the sediment (on the ocean floor) for organic material," said John Holbrook, the geoscience professor supervising the project.

"A lot of people thought these were actually a cast of fossilized tree roots," Eifert said, but the structures follow a complex pattern with small specialized galleries, "as though the marine organism was actually planning his moves through the system."

There are also no signs of root hairs, and Statler, 22, pointed out, "They just don't taper like tree roots would."

Over millions of years the burrows were filled in by limestone, which was then chemically replaced by chert, or flint, a hard, corrosion-resistant mineral.

Paleontologists now believe that burrowing behavior in large organisms didn't become prevalent until at least the Mesozoic Era, 65 to 245 million years ago, and most fossilized burrow structures dating from before that time are much smaller -- usually less than a quarter of an inch in diameter.

Like the burrow structures now being studied, most large burrow structures dating back before the Mesozoic Era are chertified, and such burrows have been found in rocks up to 600 million years old.

But Eifert, Statler and Holbrook say, trace fossil experts have held fast to the idea that those large pre-Mesozoic burrows were originally much smaller and were enlarged by the addition of layers of chert to the exterior of the burrow structure over time.

"My main objective was to determine whether these large burrows were their actual size or not," Eifert said.

An "interesting feature" Eifert found in the burrow structures now being studied suggests the burrows were chertified from the walls in, so they were not substantially enlarged during the process.

"In fact, it might be an indication of the organisms trying to reinforce the burrow for structural support," she said.

Cross-sections of the burrow structures show shell fragments "concentrically aligned around the burrow. I found some clusters of fecal pellets and grain packed around the outer rim," Eifert said. "Many marine organisms, particularly those that burrow on the bottom of the ocean floor in the sediment, will often reinforce their burrow structures to keep them from collapsing."

The project could mean a section of the paleontological record will have to re-written.

"We find burrows this size all the time in rocks up to 600 million years old," Holbrook said. "What's significant is this is some of the very first hard evidence that's been found that some of these burrows were actually that big to begin with. It could start pushing back significantly the time period when we can expect to see things that made large burrows."

Those types of organisms could be "hundreds of millions of years" older than originally believed, Holbrook said.

While Eifert is concentrating on the structures themselves, Statler's task is to try to identify what made them. He is mapping out the burrows found in the cave, and will compare those patterns to patterns known to be made by different types of organisms.

"Possibly we might even have to name the organism," Statler said.

Does that mean Statler might discover the burrows were made by a hitherto unknown organism?

"I sure hope so," he said.

"There's a good bet it was big," Holbrook said. "It wasn't a little teeny thing."

Part of the problem is there is fossil record of the organism. Marine organisms are soft-bodied, so there's nothing to preserve, Holbrook said.

In addition, the students will be able to learn quite a bit about the environment in the cave at the time the burrows were formed, he said.

The structures were found along a waterfall of the Logsdon River near the Doyle Valley entrance into the cave.

"Going upstream (from the falls) is where you find all these dark burrows here," said Eifert.

Eifert and Statler are working under the geoscience department's ERA (Early Research Apprenticeship) program, which encourages undergraduates to become involved in research and fieldwork.