Exceptional Preservation and Bias in the Fossil Record

Abstract

The three projects described herein focus on two instances of exceptional preservation and on potential source of bias in the fossil record. The occurrence of exceptionally preserved fossil assemblages and the existence of systematic bias in the fossil record from a variety of sources represent opposing forces acting on the information quality of the fossil record. Exceptionally preserved assemblages capture features of anatomy and components of assemblages not normally recorded in the fossil record. Systematic biases affecting the fossil record do the opposite, skewing our perception of patterns of diversity, the relative dominance of clades and changes in ecosystems through time. Chapter one presents the results of an analog modeling analysis to assess whether and how a newly proposed potential mechanism, the preferential sampling of larger specimens during fossil sampling due to the greater likelihood of larger specimens being intersected by a fracture surface, contributes to the lithification bias. Chapters two and three focus on the exceptionally preserved vermiform fossils from the Winneshiek Lagerstätte in northeastern Iowa and microfossils from the Doushantuo Formation of South China, respectively. Chapter two aims at resolving the identity of the Winneshiek vermiform fossils and presents evidence that these structures represent phosphatized bromalites, an ichnologic category that includes coprolites and cololites. Chapter three presents a biostratigraphy study of exceptionally preserved microfossils at three sections of the Doushantuo Formation in South China. Acanthomorphic acritarchs represent a promising tool for subdivision and correlation of the Doushantuo Formation of South China and Ediacaran strata around the world. However, the occurrence of acanthomorphic acritarchs within the Doushantuo Formation is controlled by the availability of early diagenetic chert nodules that host microfossils such as acanthomorphic acritarchs. One of these sections contains the rare occurrence of early diagenetic cherts in an upper slope section. This new biostratigraphic data adds to the growing body of integrated chemostratigraphic and biostratigraphic data from the Doushantuo Formation. By understanding both exceptional preservation and sources of bias in the fossil record it is possible to separate artifact and noise from the true signal of the history of life.