THE FOSSIL RECORD AND MACROEVOLUTION OF THE COLEOPTERA: A QUANTITATIVE ANALYSIS OF FOSSIL OCCURRENCES

Coleoptera (beetles) is the most species rich metazoan order on the planet today, with approximately 350,000 species. While many have remarked on their vast numbers, how they came to be such a diverse group is still under investigation. Here we synthesize the global fossil beetle literature to study both the taxonomic diversification of beetles and the nature of the record itself. Our database includes over 5,100 beetle occurrences from 217 fossil localities compiled from the international paleontologic and entomologic literature. We standardized the taxonomy and corrected for nomenclatural consistency. Localities were placed into thirteen 25My intervals spanning 2 - 300Ma.

Of the 143 families of beetles preserved in the fossil record, 137 (96%) belong to extant families and 6 (4%) to entirely extinct families. Beetles are found in many depositional settings, but amber and lacustrine deposits are most significant in terms of both diversity and abundance. Although amber offers superior preservation of specimens, amber deposits do not disproportionately influence the observed macroevolutionary patterns. Specifically, the lacustrine record preserves substantially more beetle occurrences, and amber deposits first appear in the early Cretaceous, failing to capture the first 165 million years of coleopteran evolution. Also, of all families preserved in the fossil record, only 40.9% are found in amber, and only 1.4% of families are known exclusively from amber deposits.

Overall sampling of beetles varies through time, with the most collections occurring in the late Jurassic through early Cretaceous, and the Eocene through Miocene. The late Cretaceous is a period of low sampling. Therefore, we used standard resampling techniques to standardize temporal variation in sampling to estimate patterns of taxonomic richness and rates of family origination and extinction. Beetles diversify early, with their highest rates of origination in the Permian and Triassic, followed by declining rates throughout their subsequent history. However, even more significant for the evolution of beetles is their low extinction rate, which pervades the entire record. Indeed, instead of focusing on the mechanisms that promote the speciation of beetles, the focus should be on why coleopteran families have such low levels of extinction.