University of Vermont

Virtual Field Study

eval

Evaluating the Findings


    The change in internal volume and shell thickness over time among Anadara and Astarte shells are evidence of evolution, due to the high correlation between directional change in morphology versus time.  How do we know that the changes we see in shell thickness and internal volume are evolution and not short-term response to an environmental stressor, such as sediment accumulation rate?   By examining the sedimentary environments in the area, Dr. Kelley determined that there was no correlation to any major environmental change, in other words, the types of rock that these fossils were found in do not record any significant changes that correspond to the incremental changes in  shell features.  Dr. Kelley was also able to negate the factors of ontogeny by determining the age of the shells based on growth lines.  While the shell features of Astarte and Anadara were observed to change over time,  other genera of bivalves studied by Kelley do not share these same results.  These genera often demonstrated non-consistent patterns of temporal change, and widely fluctuating non-directional trends.
(see below). 
Compair Diagram
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