Editor’s Note: This article originally appeared in Entomology Today, a project of the Entomological Society of America with the goal of reporting interesting discoveries in the world of insect science and news from various entomological societies. To learn more, visit www.entomologytoday.org.
Cockroaches are not 300 million years old. They might not even be 200 million years old. In fact, the oldest cockroaches known from the fossil record are only 125-140 million years old, hardly the ancient and immortal beasts claimed by some. In our paper published in Palaeontologica Electronica, a review of the oldest cockroach fossils known to science, we debunk the misconception that cockroaches have been around since the Carboniferous Period. Currently, the oldest known cockroach fossils, Valditermes brennae and Cretaholocompsa montsecana, are from somewhere around the end of the Jurassic and beginning of the Cretaceous (circa 120-130 million years ago).
There are ancient cockroach-like fossils from almost 150 million years earlier than the oldest know cockroach fossil, but these are not cockroaches. Not any more than the elegant praying mantis is a cockroach. In fact, the mantis is more closely related to the cockroaches of today than the “roachoids” from 300 million years ago. The roachoid fossils are more likely part of the group from which both mantises and cockroaches originated. However, the name “roachoid” can be confusing since it implies relatedness to cockroaches.
MAKING THE CASE. Our study applies high scientific standards set by the National Evolutionary Synthesis Center’s Fossils Calibration Database Working Group to assess which fossils are correctly classified as cockroaches. In doing so, we determined that only 25 percent of the oldest cockroach fossils could be correctly attributed to a known group of cockroach. This was because the fossils were preserved without the information necessary to determine what kind of cockroach they were or even if they were cockroaches at all.
Some fossil cockroaches are valid, though. The oldest one, Cretaholocompsa montsecana, lived in a Cretaceous version of modern day Spain. Another, “Gyna” obesa, which is the earliest known member of the family Blaberidae, was alive 50 million years ago and could be found in France, where no Blaberidae exist today. Two others are preserved in the Green River fossil deposits from Colorado and are only about 40 million years old.
The dates of these fossils indicate that most of the 7,000 species of cockroaches alive today probably originated after the extinction of the dinosaurs. Cockroaches almost certainly existed in the Cretaceous and Jurassic periods, too, but most of those lineages appear to have gone extinct. That said, all of the statistical analyses that have incorporated fossils to date the origin of cockroaches have used the fossils we believe are invalid, so the jury is very much still out on when certain groups originated. Others have stated that cockroaches probably cleaned up after dinosaurs, and our study indeed shows that cockroaches and dinosaurs shared the earth together.
We would also emphasize that accurate fossil calibrations are important for understanding the chronological history of a group. We encourage all biologists to properly vet fossils that can be used as calibrations in their groups. For more details visit: http://fossilcalibrations.org.
Dominic Anthony Evangelista, Ph.D., is a National Science Foundation postdoctoral research fellow at le Muséum national d’Histoire naturelle in Paris. Manpreet Kohli is pursuing her Ph.D. in Ecology and Evolutionary Biology at Rutgers University.