Presence-absence data for 51 plant-insect associations on 13,441 fossil plant specimens, spanning the Cretaceous/Paleogene (K/T) boundary in southwestern North Dakota, USA, provide evidence for a major extinction of insect herbivores. We investigated 143 megafloras from 106 stratigraphic levels in the Williston Basin representing 183 m of continuous section and an estimated 2.2 ± 0.1 m.y. The boundary is associated with a sharp and sustained decrease in the number and frequency of associations. The most specialized associations, which were diverse and abundant during the latest Cretaceous, virtually disappeared at the boundary along with their plant hosts, and failed to recover in younger strata even as generalized associations regained their Cretaceous abundance.

These data support two nonexclusive extinction scenarios. First is a primary and simultaneous demise of plants and their herbivores. Alternatively, there may have been secondary extirpation occasioned by host-plant extinction and the failure of herbivores to colonize remaining but chemically similar hosts. The sudden losses at the K/T boundary are in stark contrast with the more prolonged changes during the Paleocene to Eocene warming interval, characterized by a modest turnover but no net loss of associations. In conjunction with an approximate 80 % extinction of plant species at the K/T boundary, our results are consistent with a sudden ecological perturbation that precipitated a longlasting diversity bottleneck for insects and plants.