A diverse Oligocene-Early Miocene insect and plant lagerstätten has recently been identified from a sequence of paper shales in fine grained deposits found along the Canyon Ferry Reservoir, east of the Elkhorn Mountains in southwestern Montana. To date, limited excavation and preparation has lead to the discovery of 36 families of insects, and over 40 taxa of plants (leaves, seeds and stems). Trichoptera specimens have been found, most of which seem to belong to the family Limnephilidae. The relationship of these fossil specimens to extant taxa will be described in the poster.
Preservation of the fossils is outstanding, wing venation and reproductive structures often present. Structures that resemble the retreats of larval Trichoptera have also been collected from the site. The quality of the deposit compares favorably with other Tertiary insect and plant lagerstätten, such as the Green River, the Florissant and the Republic. The density of the fossil insects is high, with some layers yielding upwards of several hundred individuals per square foot. The geologic affinities of the sites are not certain, though the deposit has broadly been regarded as Oligocene/early Miocene, based on the mammal biostratigraphy, and new radiometric dates from an ash-flow tuff deposit well below the insects reveal an age of 32.0 ± 0.1Ma. The fossil deposit has both lithological and faunal/floral similarities to insect/plant paper shales found along the Ruby River, about 100km to the south.
Species 1: Trichoptera Limnephilidae
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA