49-million-year-old cockroach fossils discovered in Colorado


Three years ago, Slovakian paleontologist Peter Vrsansky found a surprise in a shipment of fossils from Rifle, Colo. Hidden in the collection was an unexpected new peek into the insect world during the Eocene epoch, 50 million years ago. Vrsansky discovered four new species of Ectobius cockroach that are five million years older – and originated from a different continent – than scientists have long thought. It turns out that Ectobius cockroaches did not originate in the Old World – Europe and Africa – 44 million years ago, but in the New World – North America – 49 million years ago.

These insects were most likely scuttling around this continent, and apparently the mountains that predated the Rockies, before even acquainting themselves with Eurasia. Scientists say that the critters must have eventually migrated through either the then-balmy Arctic and into Scandadavia, or across the Bering Land Bridge and into Eurasia.

Uncovering specimens like these, “is like putting together a puzzle, but the pieces can be moved in space and time,” said Conrad Labandeira, a co-author of the scientific paper on the discovery and a senior scientist at the Smithsonian Museum in Washington, DC.Every time you put a piece in its place, you flesh out these patterns of evolution.”

Ectobius kholsi fossils found in the Green River Formation in western Colorado. It was recently discovered that these insects lived in what is now North America, 49 million years ago.

The man who actually unearthed the cockroach specimens is David Kohls, an avid fossil hunter from Battlement Mesa, Colo. The amateur collector uncovered the fossils from bluffs overlooking the Colorado River in Garfield County, Colo. It was one of countless trips he made to the Green River Formation, and he was probably armed with a rock hammer, a wood chisel, and plenty of newspaper to wrap any delicate findings. At the time, over a decade ago, he didn’t realize the implications of his find. “But evidently it was a pretty big deal,” he said this week.

The Green River Formation, part of which is close to Kohl’s home, is a particularly good place to hunt for fossils; large, shallow lakes that once covered the area preserved a rich library of plants and animals. Plus, the formation is young enough that it escaped some long-term geological processes like erosion and metamorphism that can ruin the quality of fossils.

“For the Green River Formation, from the time of about 53 to 44 million years ago, depending on the lake, you can get a fairly accurate record of what was around in North America,” Labandeira said.

Kohls has been digging up specimens in the area since 1991, reaching remote sites by ATV and on foot. He’s donated more than a quarter of a million pieces for research, including about 47,000 slabs of shale to the University of Colorado, Boulder, and 150,000 fossilized insects to what is now the Kohls Green River Fossil Insect Collection at the Smithsonian. Scientists named one of the new species after him: Ectobius kohlsi. Less than half an inch in length, it’s a smaller version of the common American cockroaches we know today.

So if Ectobius cockroaches originated in North America, why did they disappear from the continent for tens of millions of years – until the 1940s, when they caught a ride back on imported fruit or in someone’s suitcase? Most likely, the cooler climates of the Pleistocene Ice Age drove the creepy-crawlies out. Scientists aren’t exactly sure why, but the insects survived in the Old World during that time.

Ectobius balticus discovered 1856, from the early middle Eocene Baltic amber. This specimen is several million years younger than the more recently discovered fossils. Original image courtesy of D. S. Shcherbakov.

To flesh out the implications of this new discovery, Vrsansky and Labandeira may take a look at related specimens at other museums, and also look for more fossils in the Green River Formation basins, such as lakes in northeastern Utah and the greater Green River Lakes in Wyoming. With more data, they might be able to uncover just how many types of Exobius existed here and how long they called North America home before some shipped off to Eurasia and the rest went extinct.

As for bringing in new specimens from Green River, Kohls stopped doing fieldwork a couple of years ago. From his perspective, he’s brought enough geologic history to the fore already. The hundreds of thousands of plant and insect fossils now waiting to be examined in research facilities “should keep lots of doctorate candidates busy for a while,” he said.

Tay Wiles is the online editor at High Country News. She tweets @taywiles.