It might be hard to imagine that something as thin and delicate as a fly’s wing could be preserved in rock for 55 million years. Yet this is exactly what has led to a new paleontological find in British Columbia and Washington. Scientists Dr. S. Bruce Archibald of the Department of Biological Sciences at Simon Fraser University in British Columbia have discovered a new species of insect that lived during the Eocene Epoch, or the “dawn of the recent age.”
The paper by Archibald and his associates, published July of this year in the Journal of Paleontology, describes how tiny species of extinct insects can be identified from the spidery lines of veins that lace their wings, along with other details from their minute fossils.
From these fine lines Archibald and his associates have been examining the insect superfamily Panorpoidea, also known as the scorpion fly. Today this superfamily contains only two distinct families and these flies live in North America, China, Korea, India, and Japan. During the Eocene there were three times that many. Four of this six families died out before the Oligocene Epoch 33 million years ago, leaving us with the two families that exist today. Dr. Archibald has discovered the first specimens of one of those missing families, and dubbed it Eorpidae.
Like the scorpion flies of today, Eorpidae and its missing cousins had thin bodies, delicate antenna, and four filmy wings each. The largest of them were less than an inch long. Also like their modern day counterparts, these insects would have performed an important role in the ecosystem: that of garbage men. They would have consumed dead insects and fruit on the forest floor.
Given that insects are one of the most successful classes of animals ever to roam the earth, with millions of species alive today, it is difficult to imagine why so many families of insects died out in such a short period of time.
Archibald and his associates postulate that one of the reasons might have been the temperature change between the Eocene and the Oligocene. During the Eocene, global temperatures were extremely warm and uniform, even British Columbia and Washington state would have rarely, if ever, seen a frost. The atmosphere at this time held more methane and carbon than it does now. The Eocene gave way to the Oligocene when these gasses left the atmosphere and when ocean currents began to change, giving rise to cooler and more seasonal temperatures. These cooler temperatures meant that species of Panorpoidae would have had to fly south or else adapt to cold temperatures, which the surviving species did do.
Another development that might have spelled the end for Eorpidae may have been the success of another type of insect: ants. During the Eocene, ants were becoming more diverse and more numerous. The flies would have been no match for the speed and organization of large ant colonies in the southern climates. Today, in tropical regions, dead insects only go minutes before being discovered and cleared away by ants. If you were to weigh all the insects alive, ants would make up about a third of that weight. If the Eorpidae family didn’t freeze to death it is possible that it just couldn’t compete with that kind of efficiency.
Read Archibald's study in the July 2013 issue of the Journal of Paleontology.
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