A quantitative approach to diversity, preservation, and taphonomic bias in fossil spider assemblages in lacustrine deposits

Abstract

Spiders (Araneae) are an incredibly diverse and abundant group that has colonized nearly every terrestrial habitat and existed for about 300 million years. These attributes make spiders an excellent group for investigating large scale paleobiological questions throughout geologic time. Fossil spiders are relatively rare, but are found in the geologic record as inclusions in amber and lacustrine deposits. Whereas over 1200 fossil spiders have been described, a disparity exists between amber and lacustrine fossil spiders. Compared to amber, fossil spider assemblages in lacustrine deposits are understudied with respect to taxonomy and diversity, the pathways responsible for preservation, and the biases that influence their composition. This dissertation explores fossil spider assemblages preserved in lacustrine environments to quantify the biases that influence our perception of biodiversity in the fossil record and understand the nature of taphonomic pathways in paleoenvironments of Fossil-Lagerstätten. Biases are shown here to be inconsistent across lacustrine deposits, with respect to diversity, size, life mode, and sex supporting the idea that fossil assemblages are not completely accurate representations of ancient ecosystems. In addition, microbes are interpreted to play a significant role in the unusual preservation of fossil spiders from the Oligocene Aix-en-Provence Formation of France suggesting microbial mats can be important components of the taphonomic pathway in Fossil-Lagerstätten. This dissertation expands on the evolutionary history of spiders and their preservation in lacustrine deposits, and provides a more complete view of the fossil record of spiders.