Doctor of Philosophy (Ph.D.)
Degree Granting Department
Peter Harries, Ph.D.
Paul Wetmore, Ph.D.
Brian Andres, Ph.D.
Neil Landman, Ph.D.
Mathew Olney, Ph.D.
ammonite biostratigraphy, Baculites, bivalves, phylogeny, plus ça change, Western Interior Seaway
Despite major advances, evolutionary theory still has numerous shortcomings in terms of fully understanding the controls on speciation and diversification. A major factor limiting our knowledge is how biology and paleobiology view speciation from separate micro- and macro-evolutionary perspectives, respectively. Biologists typically examine microevolutionary changes within species from various biogeographic, behavioral, morphological, and genetic perspectives, which contrasts to the macroevolutionary approach of most paleobiologists, who have examined the same phenomena at larger scales but with the standpoint of time, have also concentrated on aspects of global or regional diversification (e.g., richness, origination rates, and extinction rates) over the long-term. Noticeably absent from speciation research has been a serious reexamination of evolutionary tempo and mode (i.e., the rate and style of transformation) over the long-term framed within an environmental and phylogenetic context. These issues indicate that an assessment of evolutionary patterns set within an environmental and phylogenetic context is needed to improve our understanding of evolutionary drivers and their roles in influencing speciation and cladogenesis. Thus, the goal of this dissertation is to investigate the role that broad-scale climatic regimes (i.e., ice- vs. greenhouse conditions) play in controlling evolutionary patterns and how phylogenetic analysis can be used to reconstruct a hidden evolutionary history of a group.
To examine the role broad-scale climatic variation might exert on evolutionary dynamics, this dissertation examines evolutionary changes among nuculid and lucinid bivalves from the stable climate of the Cretaceous greenhouse to the moderately stable mixed-house climate of the Neogene to the less stable icehouse climate of the Quaternary. The bivalves used for this study include Nucula, Lucina, and Anodontia, which are well-represented in the fossil record. Morphological change through time was evaluated using both size data and elliptical fourier analysis of outline shape data. Nucula show evolutionary change during the Cretaceous and Neogene with no change from the Pliocene to Modern. Lucina, which is relatively evolutionarily conservative, show no change in shape from the Miocene to Pleistocene with substantial change in size during the Miocene and limited change in size from the Pliocene to Modern. Anodontia show change in shape during the Neogene and then no change during the Quaternary. Anodontia also shows substantial change in size and shape during the late Miocene but limited to no change in size and shape during the middle Miocene and Pliocene to Quaternary. In all cases, most evolutionary change coincided with the more stable climate regimes, whereas stasis was primarily concentrated during the less stable climate regimes. These cases provide strong support for Sheldon’s (1996) ‘Plus ça change’ model, which predicts that relatively more stable environmental settings (such as during a greenhouse or mixed-house climate regime) will display evolutionary change, whereas a more frequently changing environment (such as during an icehouse) will display stasis.
Another critical element in examining evolution in the fossil record is the reconstruction of rigorous phylogenies that allow for understanding of evolutionary relationships and modes, which usually remain hidden using traditional morphometric and biostratigraphic approaches. To reveal the hidden evolutionary history of a clade, the final chapter of this dissertation examines the evolutionary relationships of the biostratigraphically important Late Cretaceous ammonite Baculites in the Western Interior Seaway (WIS). This study used both continuous and discrete character data to construct a single most parsimonious tree using the software TNT (Tree search using New Technology). This tree has excellent biostratigraphic congruence, which is interpreted as independent corroboration of underlying evolutionary relationships among Baculites in the seaway. The tree topology reveals that middle Campanian to early Maastrichtian Baculites belong to multiple clades, which likely reflects successive extinctions of endemic lineages and replacement by new unrelated species that would evolve into new, short-lived endemic lineages. The causes for repeated clade extinction are unknown, however, they are likely related to the unique environmental conditions of the epicontinental WIS. These results suggest that non-vertebrate groups, which have typically been assumed to have a limited number of available morphological characters, can be analyzed to establish a robust phylogeny with a careful morphological analysis. The resulting phylogenetic patterns can be utilized to reveal the hidden evolutionary history of a chosen group as exemplified here for Baculites.
Scholar Commons Citation
Slattery, Joshua, "Documenting Evolution: Comparing and Contrasting Late Mesozoic and Late Cenozoic Molluscan Patterns" (2019). Graduate Theses and Dissertations.