TAPHONOMY OF FOSSIL COLEOPTERA IN THE FLORISSANT FORMATION (LATE EOCENE), COLORADO

Insect fossils are found in a variety of depositional settings, with lacustrine environments serving as the most common environment of deposition. Here we study the preservation of fossil Coleoptera preserved in the famous lacustrine deposits of the late Eocene (34.1Ma) Florissant Fossil Beds of Colorado. Specifically, we examined whether preservation quality correlates with the ability to identify specimens to various taxonomic levels. We also examined specimens from two localities, one that was near shore and the other off-shore, to study the influence of depositional environment on the preservation quality, completeness, size and orientation of specimens. Finally, we compared the diversity of Coleoptera from the two sites.

We examined 267 fossil Coleoptera from the University of Colorado Museum of Natural History Invertebrate Paleontology Collections. Specimens were scored for preservation quality and level of completeness. They were measured using digital calipers and the orientation of each specimen was recorded. We found that preservation quality was important for the identification of fossils at all taxonomic levels, with a greater proportion of identified specimens being of higher quality (x² analysis at all taxonomic levels significant at p< 0.0001). There was no significant difference in the preservation quality (x²=2.41, p= 0.66), completeness (x²=2.73, p= 0.75), nor size (F_1,265=0.173, p=0.68) of specimens found in the near shore and off-shore localities. However, there was a significant difference in the orientation of specimens preserved at the localities (x²=7.46, p=0.02), with a greater proportion of twisted specimens found off-shore. After controlling for sampling, we found no difference in the number of beetle specimens collected from each locality (x²=6.39, p=0.53), but did find a significant difference in the number of species (x²=4.84, p=0.03), with greater species richness being found in the off-shore deposit (23 near shore; 64 off-shore). Finally, the composition of species found at each locality differed greatly, with only four species in common between the two localities. Like other studies of insect taphonomy, we have found that depositional environment can play a significant role in the accumulation and preservation of insect remains.