POTENTIAL HABITAT DIFFERENCES BASED ON INSECT FAUNAS WITHIN FOSSIL LAGERSTäTTEN OF THE LATE TRIASSIC NEWARK SUPERGROUP (VIRGINIA-NORTH CAROLINA BORDER, USA)

Insects are exceedingly rare in the fossil record. Under exceptional circumstances they can be preserved at fossil lagerstätten, with details potentially allowing for a high level of taxonomic assignment. Typically lagerstätten are interpreted as having formed in deep, stagnant lacustrine environments. One example comes from the Solite fossil site within the Late Triassic Dan River Basin (Cow Branch Fm), which straddles the Virginia-North Carolina border, and the slightly older (geologically) Route 220 site. Both sites are typified by black, fine-grained shales and both have very well-preserved fossil insects. At first glance though, the faunas appear to reflect differences in habitat, which seems to counter the interpretation of all such lagerstätten as belonging to large lacustrine environments. Herein we analyze the faunal differences between these sites in order to better understand potential habitat differences that still yield lagerstätte-level fossilization.

The sample size for the Solite fauna insects that could be identified to order was high (n = 3,902) relative to ordinal level identifications from the Route 220 fauna (n = 644). This stems from a much larger overall fossil insect collection from Solite (n = 7,265) relative to Route 220 (n = 1,221). Alpha diversity under rarefaction using the freeware PAST still yielded much higher diversity at the Solite site, with no overlap in 95% confidence intervals. Simpson's indices were also higher at Solite (0.37) versus Route 220 (0.25).

Each fauna was highly dominated by one order, yet the dominant taxa were very different from each other. Dominance at Route 220 was attributed to abundant coleopterans (beetles), whereas the Solite fauna was dominated by hemipterans (true bugs). Given that greater than half of the hemipterans found at Solite were further identified to the family Notonectidae (back-swimmer water bugs), this seems like a strong indicator for a heavily dominated water environment at Solite. The relative lack of water bugs at Route 220, as well as the much greater abundance of non-aquatic beetles, seems to prefer an interpretation as a more terrestrial fossil fauna. These differences in faunal components seem to suggest that lagerstätte-level preservation may be possible in less dominantly aquatic habitats as well.