DIVERSITY AND TAPHONOMIC BIAS IN THE SPIDER FOSSIL RECORD

Spiders (Araneae) are an incredibly diverse and abundant group that has colonized nearly every terrestrial habitat and existed for hundreds of millions of years. These attributes make spiders an excellent group for investigating paleobiological questions related to diversity on a large scale throughout geologic time.

Here, fossil spider assemblages in both lacustrine and amber deposits ranging in age from Cretaceous to Miocene are compared to identify patterns in diversity and biases in preservation through time and with respect to preservation style. Each lacustrine deposit was examined to determine family richness and composition, size of individual spiders, life mode (web spinning vs ground-dwelling), and sex. Amber data was pulled from existing literature.

Fossil spiders in lacustrine deposits do not appear to be preserved in a uniform manner. Spiders in the Crato Formation of Brazil (Cretaceous) are dominated by larger aerial web-building spiders. The diversity of this Mesozoic deposit is relatively low compared to Cenozoic deposits. The Green River Formation (Eocene) appears to be dominated by smaller aerial web-building spiders, while in contrast, most spiders from Aix-en-Provence (Oligocene) are larger ground-dwelling spiders. The Florissant formation (Eocene) appears to have the highest overall diversity, while the other deposits are comparatively low. There is no clear trend in sex ratio for lacustrine deposits.

Amber deposits include Burmese (Cretaceous), Baltic (Eocene), and Dominican Republic (Miocene) ambers and appear to have a significantly higher diversity at the family level. Burmese amber has an abundance of extinct families. Baltic and Dominican ambers are dominated by web-weaving spiders. Amber also contains a higher abundance of male web-weaving spiders.

Overall, there is greater diversity in Cenozoic deposits, especially amber. It is clear that some lacustrine deposits capture a different window of the arachnid community compared to amber. The differences are likely the result of depositional environment and different taphonomic filters. The combination of lacustrine and amber data presents the most complete picture of spider diversity in the fossil record.