Date of Award

Spring 1-1-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geological Sciences

First Advisor

Dena M. Smith

Second Advisor

David A. Budd

Third Advisor

Steven K. Schmidt

Fourth Advisor

César R. Nufio

Fifth Advisor

Peter H. Molnar

Abstract

Non-biomineralized, or soft-bodied, fossils provide important paleontological information the “standard” shelly and bony fossil record cannot. Yet, a good understanding of soft-bodied taphonomy has proven elusive given the variety of histologies and preservation pathways that populate the soft-bodied fossil record. This dissertation addresses this problem using three separate but interconnected studies.

In the first study, a soft-bodied taphonomic model is synthesized by consulting the literature, with concentration on twelve soft-bodied deposits in the fossil record. This model groups soft-bodied preservation pathways into three classes based on how the microbial community effects preservation. Within each class, zones of consistent relationships between fossils and taphonomic variables are established. The model allows for different soft-bodied fossils and deposits to be compared, for tracing hypothetical soft-bodied organisms from burial to fossilization or degradation, and for the prediction of key soft-bodied taphonomic variable values in poorly known deposits. Further, the model guided the subsequent two studies.

In the second, fossil sample-based approach, the inherent taphonomic bias between mineralized, iron oxide insects and carbonaceous compressions fossil insects from the Green River Formation of Colorado is compared. Iron oxide insects are preferentially better sclerotized and preserved with less preservational fidelity and greater degrees of disarticulation compared to carbonaceous compression insects. This bias was acquired over multiple stages of the taphonomic process, not just during mineralization.

In the third, experiment-based approach, soapberry bugs were buried in taphonomic experiments that altered conditions of the burial environment. As the taphonomic model predicted, the availability of simple organic products was a limiting factor in the activity of anaerobically respiring microbes, and permeability barriers helped protect insects from decay. Contrary to expectations, insects buried in clay- and iron-rich sediment showed much greater decay than those buried in quartz sand.

The use of multiple methodologies in this work allowed for targeted taphonomic investigations and insights into connections between variables that would not have been available from any single study. A multi-faceted approach is best to address a subject as complex as soft-bodied taphonomy. Many of the results of these studies were unexpected, and open the door to future research.

Dissertation Supplemental Table 1.xlsx (70 kB)
Dissertation Supplemental Table 1

Dissertation Supplemental Table 2.xlsx (133 kB)
Dissertation Supplemental Table 2

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