REVISITING INSECT DIVERSITY IN THE FOSSIL RECORD

Insects are the most diverse group of animals and understanding how and when this extreme diversity began can provide clues about the major factors controlling diversity. Previous studies involving large databases used simple range-through diversity counts, recording only first and last occurrences, which are inherently biased and can give misleading perceptions of diversity trends. We compiled more than 18000 occurrences of more than 6600 insect genera in the Paleobiology Database to analyze patterns of insect diversification based on the fossil record. This occurrence-based database allows for calculation of unbiased extinction and origination rates and sampling-standardized diversity using the shareholder quorum subsampling method. In contrast to previous studies, which documented an exponential increase in family-level diversity, we find a two-part pattern: insects diversified in the Late Carboniferous but their diversity remained low until a dramatic increase in the Late Jurassic. Diversity remained at that higher level through the Mesozoic and Cenozoic, implying that insect diversity has been high since at least the Late Jurassic and has not increased exponentially. Although it has been widely speculated that the rise of angiosperm plants led to increased insect diversity, the Late Jurassic family-level diversity increase preceded angiosperm evolution and more likely corresponds to a change in preservation from marine/lagoon/delta to large lacustrine environments. This change has been shown to also affect preservation quality; the shift to preservation in large, deep lake deposits correlated with a dramatic increase in preservation of insects as complete bodies. Many of these lakes occur where extensional basins rapidly formed large amounts of accommodation space, which allows for the specific low-energy, high-sedimentation conditions favorable for insect preservation. This study provides a clear link between global tectonics and apparent patterns in fossil insect diversity.