3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item A comparative functional analysis of spinous process, transverse process and articular facet morphology of the upper thoracic spine in extant hominids and fossil hominins(2024) Yelverton, Christopher JamesThis study utilized three focus areas to evaluate and compare the variation in morphology of the spinous processes and articular facets of the upper thoracic spine (T1-T6) in African apes, contemporary humans, Later Stone Age (LSA) humans, baboons and fossil hominins, with the goal of finding and explaining potential functional differences. Further questions included if the spinous process deviations observed were specific to the structure or included changes to articular surface orientation and size (i.e., were changes noted only structural, or were there additional functional changes that occurred simultaneously). A skeletal sample consisting of hominines—chimpanzees (Pan troglodytes), gorillas (Gorilla gorilla), LSA humans and contemporary humans—and baboons (Papio ursinus) were compared to each other (as examples of varying locomotor propensity or lifestyle) and to relevant fossil hominins including Australopithecus africanus (Sts 14), Australopithecus sediba (MH1 and MH2), Australopithecus afarensis (A.L. 288-1) and Australopithecus prometheus (StW 573). A novel process for photography of samples was established and demonstrated to be reproducible. Specimens were photographed and linear and angular measurements taken utilizing ImageJ software and non-metric visual observations. Comparisons of hominines and baboons demonstrated statistically significant differences between species and sex. Spinous process deviations demonstrated a lower than anticipated overall incidence when evaluating the entire vertebrae sample, although the presence within an individual’s sequence of T1-T6 was significantly higher and was more prevalent in males in all groups. Morphological presentations of spinous iv process deviations were classified into five patterns based on the region of deviation identified. Age in the contemporary humans, and locomotor propensity when all selected primates were compared did not appear to have an impact on frequency of occurrence of this feature. In relation to the comparison to fossil hominins, there did not appear to be sufficient consistency in presentation to allow for this feature to be proposed as a developmental feature in the upper thoracic vertebrae related to bipedalism. The LSA humans sample group demonstrated an increased likelihood of spinous process deviations in the upper thoracic vertebrae and may be related to lifestyle and activity levels that were significantly different to contemporary humans. In summary, the study found morphometric measurements and spinous process deviation to relate more to species differences and sexual dimorphism than to locomotor differences, with lifestyle and activity levels in humans potentially increasing the frequency of spinous process deviations. It may be concluded that spinous process deviations are a consequence of various related factors that may interact in their development, or in many cases may be the result of random normal variations between individuals. Spinous process deviation in the upper thoracic vertebrae is therefore not a reliable indicator of postural or locomotor behavior in the extant comparative sample or in fossil hominins but may be an indicator of lifestyle and activity levels in humans.Item A re-evaluation of the cranial morphology and taxonomy of the Triassic dicynodont genus Kannemeyeria(University of the Witwatersrand, 2000-12-22) Renaut, Alain, JosephThe genus Kannemeyeria is one of the most important and distinctive taxa of the Triassic dicynodonts. It became the first Triassic dicynodont known to science, and thus forms the benchmark for the comparison of the evolution and morphology of other Triassic dicynodonts. An understanding of this genus forms an integral part of the biozonation of the Beaufort Group, and is pivotal in influencing the interpretation of the evolution, physiology and phylogenetic relationships of the Triassic dicynodonts. This study focuses on the detailed cranial morphology and relationships of the Kannemeyeria, and uses a rigorous morphological investigation as the basis for a meaningful elucidation of the functional and thus physiological aspects of this dicynodont. The descriptions demonstrate that variations related to the skull size, distortion or naturally occurring variation within the genus allow for the synonymy of the formerly recognised species K. latifrons Broom (1898; 1913), K. erithrea Haughton (1915) and K. wilsoni Broom (1937). This conclusion is further supported by the allometric analysis which cannot distinguish the variation observed in the holotypes with that occurring naturally within a growth series. Apart from the large specimen, the other smaller individuals are accommodated in the genus as different ontogenetic stages of the growth series represented by K. simocephalus Weithofer (1888). Several allometric variables show unusual patterns of development, indicating that Kannemeyeria can be subdivided into ontological classes, as juvenile and adult forms, separated from each other by a particular level of development. An age-related threshold level is suggested, and considered to represent an animal reaching sexual maturity. It is consequently proposed that the Kannemeyeria population was, at an age-related level, subdivided into sexually mature and immature groups but remained ecologically homogeneous. Both the descriptions and the allometric analysis of the species K. cristarhynchus Keyser & Cruickshank (1979) clearly indicate that it does not conform to the growth series of K. simocephalus and thus the differences observed between these two taxa are not constrained to size increases. Consequently, the recognition of the species K. cristarhynchus is considered valid. From the observations of the cranial morphology, tested using an allometric analysis, generic and specific diagnoses are constructed for Kannemeyeria and its two African species. Several features of Kannemeyeria are discussed in a functional context. A corrugated hom-covered snout and large caniniform processes are considered to be associated with defence and posturing behaviour. Several features of the braincase also suggest herding behaviour. Kannemeyeria also has a slightly different occipital musculature arrangement than that proposed for many other dicynodonts. Most Kannemeyeria cranial features are related to its masticatory function. From the analysis of masticatory cycle it is clear that the jaw action is described via a single pivot-point, which in Kannemeyeria approached the original, primitive position of the jaw hinge. The vertical orientation of the articulation and this pivot-point ensured that the muscle action during second phase of mastication produced an upward crushing and grinding action instead of the typical fore-and-aft motion of many other dicynodonts. It also meant that the muscle force was at their maximum, and little or no energy was lost to translation of the moment arm at the jaw articulation. Consequently, the Kannemeyeria masticatory cycle was both highly effective and extremely efficient. The morphology, and resultant physiology, of Kannemeyeria skull is considered to represent the innovative foundation for much of the success of many of the later Triassic dicynodonts.Item Longevity, population stage and size structures, morphology and reproduction of four long-lived grassland suffrutices(2012-01-18) Dayaram, AnishaLittle is known about the longevity of grassland suffrutex plants and the relationship between longevity and plant morphological structures and seedling growth strategies. The aim of this study was to determine the longevity of four grassland suffrutex plant species, namely Berkheya insignis, Callilepis laureola, Protea insignis and Tephrosia kraussiana. Seed viability, seedling growth, morphology, habitat and population structure and demography were also assessed and related to plant age. The rhizomes, seeds (if available) and canopies of B. insignis, C. laureola, P. simplex and T. kraussiana were removed from a site near Port Edward in the Pondoland region, KwaZulu-Natal, South Africa in April 2008. Seeds were available for P. simplex and T. kraussiana only. Seed germination and viability were tested in the field and laboratory using germination trials and tetrazolium tests. Greenhouse and field grown seedlings were used to monitor seedling growth and to record seedling morphology. The aerial and rhizome morphologies of adult plants excavated from the field were also recorded. The largest of these rhizomes were aged using radiocarbon dating. Attempts were made to develop morphological surrogates for plant age as no method currently exists. Plant density, demographies, number of inflorescences and various environmental variables of wild populations of B. insignis, C. laureola, P. simplex and T. kraussiana were sampled from the Red Desert Nature Reserve and the Umtamvuna Nature Reserve. Species morphologies varied, however important similarities suggest convergent evolution. These included a single vertical main stem rhizome with multiple side branches, early rhizome development in seedlings, and high root: shoot ratios. Seed viability was high in the laboratory but low seedling emergence was observed in the field. Seedling growth was rapid for T. kraussiana and slow for P. simplex. The population stage structure for all four species comprised primarily adults with few or no juveniles. Wild population plant height and main stem diameter followed normal distributions. Number of stems, basal area, canopy area and the number of floral structures had distributions favouring the smaller size classes. Soil P, N, K and organic carbon were important soil nutrients in a PCA analysis of the habitats of the four species. Radiocarbon dating yielded the following ages: B. insignis: 49-51 years, C. laureola: 49-50 years, P. simplex: 49-51 years and T. kraussiana: 51 years. There was a significant relationship between rhizome mass and canopy area, basal area, height, number of stems and main stem diameter. Since rhizome mass had a positive relationship with age- a relationship between age and aerial structures is likely. Therefore, creating surrogates for age may be possible. Overall, these species have moderate longevity, are poor seed producers with possibly slow population growth and are closely associated with soil nutrients. Therefore, these and other suffrutex species are particularly vulnerable to habitat destruction and climate change. The results of this study indicate that there needs to be a greater focus on below ground growth during ecological assessments in order to better understand the ecology of our diverse grassland biome plants.