The fossil record is the only direct source of data for studying modes (patterns) and rates of morphological change over geologic time periods. Determining modes is critical for understanding macroevolutionary processes, but just how modes can vary within a taxon, and why, have hitherto been largely understudied. To address this, I examined patterns of morphological change in the shell of the Mesozoic marine bivalve genus Buchia over its geographic and temporal range. Buchia was chosen as a test subject because it is abundant, well-preserved across a variety of facies,
and is widely distributed across the Northern Hemisphere where the likelihood of
multiple lineages is low. While the focus of this thesis is on evolutionary patterns, it
is also necessary to address issues of taxonomy and geographical variation, making
this research applicable to a wide-variety of fields.
Previous to this study there was no protocol for measuring buchiid valves, nor was
the genus studied in a quantitative manner. Throughout this research I used ten
morphological characters to describe shell shape and size. Multivariate methods
(principle component and canonical variate analyses) were employed to discriminate
between species of Buchia and examine how morphological characters change through time and space within the genus. Evolutionary patterns were delineated using two well-established programs that discriminate between multiple modes of evolution. Overall, nearly 2000 specimens from eight geographical locations around the world were studied for this thesis.
I found the genus Buchia was a useful tool for evolutionary studies as it can be
studied quantitatively in space and time. Specically I have found that buchiid species can be delineated using morphometrics; the genus is restricted to the Northern Hemisphere; while the environment significantly affects morphology, there is no
evidence of a latitudinal gradient; diversity and disparity within Buchia are not correlated; most evolutionary modes conformed to random walks or stasis; and modes and rates vary across the geographical range of the genus. Overall, I have found that the environment plays an important role in shaping both morphology and modes.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/4654 |
| Date | 05 1900 |
| Creators | Grey, Melissa |
| Publisher | University of British Columbia |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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