The fossil insect assemblages discussed here comprise 122 assemblages,
analysed from 13 sites, ranging from northern Montana
to southern Colorado. In all cases, insect fossil remains were
extracted from unconsolidated, organic-rich sediments using the
kerosene flotation method described in Elias (2010). The fossil
specimens recovered by this process are, for the most part, individual
sclerites rather than whole exoskeletons. Beetles (Coleoptera)
dominated all the assemblages, but other insect orders
represented in some assemblages include ants (Hymemoptera:
Formicidae), caddisfly larvae (Trichoptera) and true bugs (Hemiptera
and Homoptera). Only the beetle results are reported here.
Fossil identifications were based on comparison with modern
museum specimens, modern specimens in the author's collection,
with the aid of taxonomic literature, and by taxonomic specialists in
some families, as noted in the acknowledgements