The Collections Highlights series profiles notable fossil collections curated and housed in the Department of Paleobiology.
Over the last five years, Dale Greenwalt, a volunteer and research collaborator working with Paleobiology curator Conrad Labandeira, has assembled an amazing collection of tiny but beautifully-preserved fossil insects from northwestern Montana. He collects the 46-million-year-old fossils at sites along the edge of Glacier National Park where the Flathead River cuts through fossil-rich rock, the Kishenehn oil shale, which formed at the bottom of an ancient lake. Not surprisingly, the fossils preserved within the shale are mostly species that spent part or all of their lives living in or near the water. About 45 percent of the specimens are midges or similar insects, and another 15 percent are water boatmen of various types. The rest include other flies, mosquitoes, wasps, beetles and aphids - to date, 14 different orders of fossil insects have been collected.
Most of the insects are very small - under half a centimeter (1/4 inch) in length - but the quality of preservation is incredible. Viewed through a microscope, minute hairs, wing veins and other small structures can be seen. Many of fossils preserve pigments and color patterns.
Of the thousands of fossils that Dale has collected and photographed, one of the most astonishing is the adult midge shown below left, preserved just as it emerged from its pupal case. Midge wings are compressed when still in the pupal case, but they expand rapidly as the adult emerges. The wings of this adult had not had a chance to expand to full size.
The fossil of an adult midge that had just emerged from its pupal case is shown on the left. An unexpanded wing extends toward the right, and the part of the pupal case that held the insect's abdomen extends toward the bottom of the photo. Fossils of a fully developed adult (top) and a pupa (bottom) are shown to the right, for comparison. Blue arrows point to the wings. Red arrows point to the abdominal portions of the pupal cases. Photos by Dale Greenwalt.
The Kishenehn fossil insect collection is a notable for its size (16,000 fossils and growing) as well as its extraordinary preservation, and it has quickly become a valuable resource for scientists studying many aspects of insect evolution.
Fossil collecting on the North and Middle forks of the Flathead River, both of which have been designated as Wild and Scenic Rivers by the U.S. Congress, is strictly regulated by the United States Forest Service. Permits are required.
An article about the Kishenehn fossil insects by Dale Greenwalt and Conrad Labandeira appears in the September/October 2013 issue of Rocks & Minerals:Dale Greenwalt & Conrad Labandeira (2013) The Amazing Fossil Insects of the Eocene Kishenehn Formation in Northwestern Montana, Rocks & Minerals, 88:5, 434-441, DOI: 10.1080/00357529.2013.809972
Read an earlier post about our collection of Green River fossil insects.
A video showing adult midges emerging from their pupal cases is on YouTube. A full emergence sequence starts 31 seconds into the video.