Electronic Theses and Dissertations (PhDs)

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Browsing Electronic Theses and Dissertations (PhDs) by Department "Evolutionary Studies Institute ESI"

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    Late Quaternary Palynological Studies at Lake St Lucia, KwaZulu-Natal
    (University of the Witwatersrand, Johannesburg, 2023-08) Effiom, Angela Charles; Neumann, Frank; Bamford, Marion
    Palynological studies were done on lacustrine sediments deposited during the last ~6300 and about ~2000 cal yrs BP in Mkhuze Swamp, which drains into the most northern part of Lake St Lucia located in the Indian Ocean Coastal Belt Biome of KwaZulu-Natal, eastern South Africa. The aim was to reconstruct the past vegetation and to infer past climate fluctuations as well as human disturbances to complement growing evidence from other disciplines about these questions in the area. Following standard palynological methods, samples from two cores Mkhuze River Delta (MKD-1, long core) and Mkhuze swamp (MK24-1, short core) were extracted and analyzed. Palynological results for both cores show a dominance of Poaceae (20-90%) suggesting a strong influence of grassy woodland savanna. Spirostachys pollen dominated the arboreal spectra of the pollen profile in MK24-1, but it dominated the arboreal pollen spectra for the last 2600 cal yrs BP in MKD-1 as Podocarpus pollen dominated the arboreal spectra from 6300-2600 cal yrs BP indicating a change from a forested environment to a more open woodland environment. The results also show that the mid Holocene was humid with high precipitation and high sea level while the late Holocene was warm, dry with Marine influence (more sea water flowing into the lake due to high evaporation and low fresh water supply caused by drought). Similar pollen fluctuations were observed in records from Lakes Eteza and Sibaya also located within the Indian Ocean Coastal Belt Biome. The presence of Pinus pollen at the top of the profiles suggests the onset of European settlement when pines were introduced for timber production. Other published pollen records from the region in the last ~7000 cal BP show a general trend from a mesic forested environment towards an open woodland environment with grasses which is due to climate change.
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    Reassessment of the Phylogeny of Basal Therapsida Using Micro-Tomography and Bayesian Phylogeny
    (University of the Witwatersrand, Johannesburg, 2023) Duhamel, Alienor; Rubidge, Bruce; Benoit, Julien
    This PhD research is focussed on the evolution and cranial anatomy of the earliest therapsids. The Therapsida is a paraphyletic group of land tetrapods that lived mostly during the Permian and Triassic Periods. They emerged quite suddenly in the fossil record during the middle Permian, already showing diversification into five distinct groups: Biarmosuchia, Dinocephalia, Anomodontia, Gorgonopsia and Therocephalia. A sixth group, the Cynodontia, appeared during the late Permian. Of these, the anomodonts, therocephalians, and cynodonts survived the devastating Permo-Triassic mass extinction and continued to be the dominant tetrapods during the Early and Middle Triassic Periods. Ultimately, the cynodonts would evolve into the earliest mammals. Chapter 1 introduces the scientific questions tackled in this thesis. Chapter 2 provides the necessary explanations about the material and methods used for this work. The use of CT-scanning technology allows for the detailed examination of cranial internal morphology, with the goal of incorporating inner cranial characters into a phylogenetic framework. Chapters 3 and 6 focus on the fossilisation gap at the early to middle Permian transition, which has led to debates over the timing of the early diversification of the Therapsida. In Chapter 3, the geologic position and anatomy of one of the oldest known therapsids, Raranimus dashankouensis is reviewed. The chapter concludes with a reassessment of the basal phylogenetic position of Raranimus and suggests a Roadian origin for the taxon. Chapter 6 presents a comprehensive analysis of cranial morphological characters based on the descriptions and findings from Chapters 3, 4, and 5. Using both traditional maximum parsimony and clock-based Bayesian inference of phylogeny for the first time on the Therapsida, the results suggest that therapsids originated around 280.5 million years ago and rapidly diversified into several distinct clades during the Kungurian and Roadian Epochs. The phylogenetic relationships of several taxa are reevaluated and the findings suggest that Biseridens is more closely related to the Dinocephalia and Biarmosuchia, rather than the Anomodontia. Furthermore, the results suggest that Sinophoneus may represent the basal-most dinocephalian, and that Therocephalia might be paraphyletic. Therapsids were characterised by a wide range of cranial morphologies, with the Biarmosuchia and Anomod ontia exhibiting distinct cranial features. Both groups are considered basal among therapsids. Chapter 4 of this PhD research focuses on the postnatal ontogenetic development of cranial ornamentation in Biarmosuchia and possible impact on phylogeny. The results suggests that cranial bosses and ridges are ontogenetic features and the parietal bone originates from multiple centres of ossification. Chapter 5 is a comprehensive cranial description of several basal anomodont specimens. The Chapter concludes with a review of the taxonomy of the genus Eodicynodon and proposes the creation of a new taxonomical unit for specimen NMQR 2913.