Hard labor at Bear Gulch

Natural History, July-August, 2006 by Eugene H. Kaplan

Grumpy, fuzzy, scholarly type was beside himself. Halfway up the ten-foot-high rock wall he'd run out of toe-holds, and he clung desperately to the tiny fingerholds above him. The wall was made of layers of shale, inch-thick ledges protruding irregularly from the mesa, and he couldn't find a higher one to stand on. The distinguished professor of physiology and evolution was stuck.

I pushed on his bottom. Someone pulled him from above. Finally he scrabbled onto the top of the mesa and fell, prostrate, on the flat, hard, dusty surface. After a minute he rolled over, tears of exertion still in his eyes.

About ten people toiled atop the mesa, all paleontologists. We were prospecting for fossils at one of those small, scarcely known paleontological

sites that abound in the western United States. This one--Bear Gulch--is situated on a cattle ranch in central Montana. The leader of our team had written profusely about shark fossils of the Mississippian period, 300 million years ago. Back then, Bear Gulch was an inlet of what was to become the Pacific Ocean. Warm and shallow, it was a perfect pupping ground for sharks. Occasionally a juvenile shark would die there and sink to the seafloor, soon to be buried in the soft, oxygen-poor bottom mud.

Those rich, shallow waters teemed with plankton. They, too, sank to the bottom when they died, forming a layer on top of the mud. Bacteria dined on them, oxidizing the protoplasm of the dead plankton layer. Reproducing every twenty minutes, the bacterial masses used up virtually every molecule of available oxygen. In this oxygen-starved burial place, the shark carcasses remained intact until the mud, gradually and under immense pressure, became stone--shale. Along with their encasement of mud, the tiny sharks turned to stone. Three hundred million years later, a team of toiling paleontologists broke into their tombs and let the sunshine in.

The graduate students punctuated their jolly conversations with grunts of exertion as they pried up layers of the petrified mud. The technique was to slip the sharp end of a five-foot steel spike into the junction between two layers and pound at the seam until the layers loosened. Then they would wedge the spike into the shale and lever it upward, breaking off a slab a yard or so wide. When the slab was turned over, it would usually reveal ... nothing. But occasionally a more professional-sounding grunt drew everyone's attention to a digger who had found, in all its perfection, the imprint of a tiny shark, its scales defined and its eyes turned upward in a stony stare.

My fuzzy, distinguished colleague and I also grunted frequently while we worked--not to prove we were just as professional as the grad students, but because our aging bodies made it hard to lift the heavy layers of rock. Sweating under a glaring sun, we finally learned how to use mechanical advantage, wedging up pieces of shale with the best of them. Nevertheless, the flat undersides of slab after laborious slab had nothing to show us.

Finally the two of us came upon a curled object--shaped like a sinuous peanut--embedded in the shale. Excited, we dragged the two-foot-wide chunk of rock to the head honcho, who stared at it intently and informed us it was a coprolite. We looked at him quizzically. "It's petrified fish feces" he explained. All that labor and exhaustion only to fred ancient fish poop!

The team worked until dark, our labors illuminated by a magnificent, luminous sunset. After dinner that evening the buttes and mesas rang with laughter as we were presented with our hard-won trophy--the coprolite-which, to this day, lies in state in the glass-fronted case that doubles as my class museum. Thoroughly tired, and mildly amused by our moment of triumph, I crawled into my tent, pushing at its nylon floor to carve out a flat space amid the ubiquitous cow flops. A pat of "prairie pancake" was my pillow.

The next day, another grunt brought us running. Although the fossil turned out to be of little interest to this group of ancient-shark specialists, to me it was a real treasure. I let loose a holler. There on the underside of the rock was a small, perfect, 300-million-year-old replica of a modern-day horseshoe crab.

Eugene H. Kaplan is Axinn Distinguished Professor of Conservation and Ecology at Hofstra University, in Hempstead, New York. This story is adapted from his book Sensuous Seas: Tales of a Marine Biologist, which will be published in August by Princeton University Press.