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Title page for ETD etd-07172017-161410


Type of Document Master's Thesis
Author Gibson, Brandt Michael
Author's Email Address brandt.m.gibson@vanderbilt.edu
URN etd-07172017-161410
Title Ediacaran-style Decay Experiments using Mollusks and Sea Anemones
Degree Master of Science
Department Earth and Environmental Sciences
Advisory Committee
Advisor Name Title
Simon A.F. Darroch Committee Chair
Neil P. Kelley Committee Member
Ralf Bennartz Committee Member
Keywords
  • sea hares
  • death mask
  • taphonomy
  • Ediacaran
  • anemones
Date of Defense 2017-04-26
Availability restrictone
Abstract
We perform Ediacaran-style decay experiments on both sea anemones (Condylactis gigantea) and sea hares (Dolabella auricularia) in order to test between several proposed models of control on ‘death mask’ style preservation. Specifically, we test comparisons of rates of decay, patterns of decay, and better quantify the black ‘decay halo’ precipitate noted in previous work. The results demonstrate a necessary threshold of dermal rigidity for ‘death mask’ style preservation, as well as potentially help test between diploblastic vs. triploblastic affinities for Ediacaran organisms. We find that while rate of decay was decelerated under Ediacaran-style conditions, pattern of character loss in both diploblastic and triploblastic organisms was conserved from the baseline experiments. Geochemical analyses of sediment from around the carcasses indicate that previous models of ‘death mask’ preservation might need to be assessed further as precipitation of FeS or clay mineral precursors may be decay-rate-dependent or affected by overall tissue lability of the carcass. Patterns of character loss associated with both the anemones and mollusks demonstrate a bias against preservation of the most labile tissues, such as anemone tentacles and internal gut system of the mollusks. Such biases have likely affected previous interpretations and controversies of the affinities of some iconic Ediacaran and Cambrian organisms. According to our results, absence of evidence for some of these features might be more closely linked with dermal lability rather than absence of feature all together.
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