Insights into the microbial degradation of bones from the marine vertebrate fossil record: an experimental approach using interdiciplinary analyses

Abstract

Researchers rely on the fossil record to understand and predict changes in faunal composition and evolutionary trends associated with climatic change. However, taphonomic processes such as scavenging, transport, and weathering, significantly influence the type and quality of information preserved in the fossil record by filtering and diminishing the fidelity of ecological data. To help account for taphonomic biasing, I developed a series of interdisciplinary approaches to better understand the role and characterization of microbes during the fossilization of vertebrate remains, and an additional study that improves a well-established method for estimating time averaging of fossil bone accumulations. To better understand which bacteria are responsible for bone decay, I simulated aspects of natural whale-falls by adding defleshed bones to mesocosms made of natural marine mud and water. Sequencing the V3 region of the 16S rRNA taxonomic identifier gene of bone-associated microbial communities indicated that the dominant bacterial groups exploiting bone nutrients were taxa within the Alphaproteobacteria, Deltaproteobacteria, Gammaproteobacteria, and Epsilonproteobacteria, as well as Bacteroidetes and Firmicutes. Relative abundances of these bacterial groups changed throughout the experiment, reflecting four community successions. Sulfidic framboids were observed on the experiment bone surfaces within one week and were interpreted to form as the result of reducing conditions within a dark-colored microbial mat overlain by oxic waters. When compared with published sedimentary framboid populations, the bone-hosted framboids were most similar to framboids formed in anoxic water-columns, even though the bone was overlain by oxygenated conditions, suggesting that the growing periods for framboids are shorter on bone surfaces than those in sediments and do not reflect geochemical conditions. Bone surface texture is known to degrade in a predictable fashion due to subaerial exposure, and can thus act as a proxy for estimating post-death/ pre-burial time since death which is relevant for assessing time averaging. In the final dissertation chapter I show that traditional weathering analyses can be characterized using quantitative textural analyses from 3D scans of bone surfaces. Quantifying bone weathering analyses may enable more reliable comparative taphonomic analyses by reducing inter-observer variations and by providing numerical data compatible for use in multivariate statistics.