Date of Award
Master of Science (MS)
Dr. Christopher A. Sheil
The study of developmental systems may help to resolve the disagreement between morphological data and molecular data when it comes to the placement of Testudines among Amniota. Among other unique morphological adaptations, turtles possess an anapsid (unfenestrated) condition of the temporal region of the skull. If turtles are descended from diapsids, as molecular data suggests, this implies a rapid transformation of the temporal region from the diapsid condition to the anapsid condition. This study specifically addressed temporal bone heterochony among amniotes using the methods of Continuous Analysis (Germain and Laurin 2009) and Parsimov-based Genetic Inference (Harrison and Larsson 2008) to analyze cranial ossification sequences from representative taxa of all major orders of amniotes. In addition to the use of Continuous Analysis (Germain and Laurin 2009), this study recorded the internodal heterochronies reconstructed with this method. A smaller, complete dataset was analyzed by Continuous Analysis and PGi so that a direct comparison of the methods could be made. A larger dataset with missing data was also analyzed by PGi. Each analysis had three iterations for the three supported placements of Testudines within Amniota. With the data used in this study, I was also able to empirically assess the hypothesis that endochondral bones shift more often during evolution than dermal bones. Endochondral bones were not found to shift any more often than dermal bones during the course of evolution. The results of the analyses of the smaller dataset do not support any particular placement of turtles over another. However, the results of the analyses of the larger dataset support Testudines as sister to all of Diapsida.
Sagarin, Kathleen, "HETEROCHRONY OF CRANIAL BONES IN AMNIOTA AND THE PHYLOGENETIC PLACEMENT OF TESTUDINES" (2016). Masters Theses. 18.
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