A Prehistoric Insect from Alaska's Badlands
Don Triplehorn, a University of Alaska geologist for more than 30 years, is using his retirement to pursue mysteries in rock that didn’t mesh with his teaching and research duties. He asked me to join him on a recent excursion to search for the remains of an insect that died more than six million years ago.
We drove to a gully near Healy, Alaska, that looks like the badlands in South Dakota. Bare white walls streaked with lines of red, orange and black rose from the gully in fragile spires of sandy rock rising like icicles to blue sky. Underfoot was a walkway of mud and rock with the look and feel of wet cement. This ribbon of brown masonry is replenished by spring runoff and summer rains that scrape the canyon walls free of vegetation and keep it looking like the Badlands.
Through this moonscape, Triplehorn hiked in rubber boots, followed by Syun-Ichi Akasofu, director of the International Arctic Research Center. We paused where bands of flaky black rock—the coal for which the region is famous—intersected the creek.
On an earlier trip, Triplehorn and his wife Judy collected a dozen fossils of prehistoric insects from silky smooth shale exposed by the creek. These bugs etched into rock are among a handful of insect fossils found in Alaska; just two other groups of scientists have reported collecting them in the state.
Triplehorn stopped us at a narrow point in the canyon where the walls appeared to be made of sand. Within the walls were white stripes, deposits of ash from a volcano active about 6.5 million years ago. Below the ash layer was smooth gray rock that contained fossilized insects.
Triplehorn outfitted Akasofu and me with magnifying glasses and told us to find comfortable seats amid the flakes of weathered gray rock. The rock, broken like slices of bread, was the bed of a prehistoric lake, Triplehorn said. The lake flourished millions of years ago, before the Alaska Range began its rise from the earth. At that time, interior Alaska was as flat as a tortilla and all rivers drained south to Cook Inlet and the Gulf of Alaska. Five or six million years ago, tectonic forces pushed up the Alaska Range at a speed that made Mt. McKinley grow about one centimeter each year. The rise of the mountains dammed the large lake, which filled with sediment, and died.
When the lake was still thriving, flying ants were among the many creatures of the forests and swamps that were to become interior Alaska. They were plentiful enough that many became victims of birds and insects near the lake. Before eating the flying ants, predators clipped off the wings, which were made of the same material as our fingernails and offered neither nutrition nor chewing pleasure. These wings dropped to the bottom of the lake and settled in the muck. Year after year, more sediment covered the ant wings as the lake filled in and eventually turned to stone.
Holding this stone in our hands, Triplehorn, Akasofu and I squinted at specks on the flat surfaces. In a few minutes, Triplehorn made a discovery.
“I found one,” he said.
Holding a palm-size section of lake bottom, Triplehorn pointed to a narrow brown teardrop on the flat stone. The size of a grain of rice and the color of milk chocolate, the teardrop had a network of veins characteristic of an insect wing. We passed the rock around and saw the device used to keep a flying ant aloft six million years ago, on a day perhaps not unlike the sunny August day we were experiencing.
Though Alaska’s climate, landforms and wildlife have changed many times since that ant was alive, its brief window of life may not have been that much different than ours. David Grimaldi, an entomologist with the Museum of Natural History in New York to whom Triplehorn sent the first fossils, said the species of flying ant preserved in rock are similar to those living today in Alberta, Canada.
