The Integration Of Morphology, Variation, And Phylogenetics To Better Understand Fossil Taxa And Their Modern Relatives

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Doctor of Philosophy (PhD)
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Earth & Environmental Science
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Morphology, or shapes, particularly of bones, is important for understanding how animals vary and, therefore, for understanding diversity. Comparison of morphology in animals can be used to make inferences on fossil organisms. At its base, fossil specimens are described and compared with other fossil and modern specimens, often to determine if they represent a new and distinct species, thereby increasing observed biodiversity through time. Dromaeosaurids (family Dromaeosauridae) are a group of dynamic, swift predatory dinosaurs, that have a sparse fossil record, particularly at the time of their extinction near the Cretaceous-Paleogene boundary. A recently recovered specimen from the latest Cretaceous of New Mexico represents a new genus and species and is the first diagnostic dromaeosaurid from the Maastrichtian of the southern United States (southern Laramidia). The specimen also reveals aspects of this dinosaurs behavior, including potential wounds or injuries consistent with an active predatory lifestyle, features that would have made it agile, and the presence of feathers on its forelimbs. The evolutionary relationships of this dinosaur were explored through phylogenetic analysis and shows multiple lineages of these dinosaurs at the end of the Cretaceous in North America. Additionally, the Maastrichtian members of these dinosaurs would have also been living in the same environments as the largest terrestrial predators known, the tyrannosaurids, with different species in the north and south living alongside different tyrannosaurid species, creating complex ecosystems with different sized predators presumably utilizing different predatory methods. Emydids (family Emydidae) are the most diverse and widespread family of turtles in the New World. Their fossil record is relatively well known, but more complete fossils are less common and little work has been done to understand the relationships of potential fossil members. New species within both subfamilies (Deirochelyinae and Emydinae) from approximately 5 million years ago increase our knowledge of the past biodiversity of the group. A new painted turtle helps show how Chrysemys has migrated through time and part of these biogeographic changes are controlled by temperature and climate conditions. A new species of Emydoidea represents the southern-most occurrence of the genus and suggests the physiological requirements of the species have changed through time. A new species of Terrapene shows features consistent with an aquatic or semi-aquatic lifestyle, and its position basally within the genus lends further credence to the hypothesis that the genus evolved from aquatic or semi-aquatic ancestors and has evolved to become more terrestrial through time. The new species also help researchers better understand previously known fossil species. Several fossil species considered to represent Chrysemys are found to be basally within the subfamily and potentially outside Chrysemys. Emydoidea lies phylogenetically close to Emys and is part of a clade of emydine turtles that can at least partially close their shells. Features of stem Terrapene species suggest features of T. ornata are basal and further suggests terrestrially has evolved multiple times in the genus or that there have been multiple reinvasions of the water. These studies look at morphological variation to determine the distinct nature of several new fossil species and use phylogenetic analyses to hypothesize evolutionary relationships. This information can be used to make inferences of the direct groups studied and closely related groups, but also can be used to investigate ancient ecosystems and local and regional habitats and climates, along with more generalized larger-scale conditions. These continue to add to our knowledge of biodiversity and increases the information and data we have to use toward further future studies as well.

Peter Dodson
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