Shanan E. Peters
Contingency Examined: Does the Development of Life Rely Strictly on Chance
The evolution of life on this planet was a grand experiment--an experiment in which there is a seemingly endless array of variables. Fortunately for us, the experiment seems to have been a success. Life evolved. But how dependent is the existence of a present-day genus on the success of an earlier form? Some maintain that the existence of a sentient member of Animalia is a happy accident, totally contingent upon the success of some earlier form. In the following, however, I propose that the evolution of large taxonomic groups is not strictly contingent upon the success of any single pre-existing organism, but only on 1) the origin of life, and 2) the origin of the metazoan. Also, the probable limit in number of phyla is explored as well as the physical and biotic constraints on rate and direction of evolutionary pathways.
The Dunkard: A Background and Case Study of a Location Yielding Well Preserved Plants and Aquatic Organisms
The Dunkard depositional basin was a tropical complex of alluvial, fluvial, lacustrine, and brackish-water sedimentary environments similar to those found in the lower Mississippi River Valley today. Seasonal fluctuations in runoff volumes resulted in local flooding and cyclical sedimentation. High-water events often destabilized stream channels, leading to crevasse oversplays and subsequent meandering of streams. A site in Monroe County, Ohio has been interpreted to preserve muds accumulated in an oxbow lake formed following one such oversplay event. The site contains exceptionally well preserved Neuropteris leaves and several unidentified soft-bodied organisms. The lake was apparently stratified, with slightly reducing conditions prevailing at the sediment-water interface, as bioturbation is not observed.