Masters Degrees (Zoology and Entomology)
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Browsing Masters Degrees (Zoology and Entomology) by Author "Botha-Brink, Jennifer"
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Item Open Access Comparative bone histology of stigmochelys pardalis (leopard tortoise), with specific reference to ontogeny and biomechanics(University of the Free State, 2017-01) Botha, Alexander Edward; Botha-Brink, JenniferTestudines are a group of reptiles characterised by the presence of a shell comprised of bony shields. Stigmochelys pardalis is the most widely distributed terrestrial testudine in southern Africa. Although relatively common with some life history traits (e.g. lifestyle, reproduction, longevity) being well known, the growth of this species has yet to be studied in any detail. This study is the first to use bone histology and microanatomy to examine the growth and biomechanics in an ontogenetic series of S.pardalis. The study also indicates clear short-comings in the determination of lifestyle using a single section on the diaphysis in S. pardalis and possibly in other testudines. The bone microanatomy of this clade differs from that found in other amniotes. In other amniotes, aquatic species tend to display large osteoporotic bone with large infilled medullary cavities and thin cortices. Semi-aquatic species have thick bone walls with small or no medullary cavities whereas terrestrial species tend to have thinner bone walls, open medullary cavities and a sharp transition from cancellous to compact bone. A detailed histological analysis of the limb bones of S.pardalis reveals extensive variation through ontogeny. Cortical bone becomes increasingly thicker through ontogeny and is finally resorbed in the late sub-adult stage, resulting in a thin cortex and a large infilled medullary cavity. The predominant bone tissues are parallel-fibred and lamellar-zonal for forelimb and hind limbs respectively. In certain cases parallel fibred bone tissue transitions to lamellar-zonal bone tissue later in ontogeny. A few older individuals exhibit and External Fundamental System indicating that the growth rate had decreased substantially by this stage. However, these individuals are between 56% and 60% maximum known size indicating that this slow growing species takes many more years to reach its maximum body size. Inter-elemental variability is most prevalent between the forelimb and hind limb. Forelimb elements exhibit characteristics such as faster growing parallel-fibred bone tissue, slightly higher vascularisation and a predominance of annuli over Lines of Arrested Growth compared to the hind limb which exhibits poorly vascularised, slower growing lamellar zonal-bone interrupted by LAGs. These differences indicate that the forelimb grew more rapidly than the hind limb, possibly due to the method of locomotion typical in chelonians. Lifestyle inferences using Bone Profiler indicate an aquatic lifestyle for this species despite it being clearly terrestrial. Sections from individuals of various ontogenetic stages were tested and although the microanatomy of the bone changes dramatically with age, the lifestyle readings remained inaccurate. The extensive bone resorption that occurs from the early sub-adult stage destroys much of the primary cortex, thus destroying the ecological signal. This supports the results from other studies that have found that using bone microanatomy to determine lifestyle in testudines is inaccurate.Item Open Access The postcranial skeleton of the Early Triassic non-mammalian cynodont Galesaurus planiceps: implications for biology and lifestyle(University of the Free State, 2009-12) Butler, Elize; Botha-Brink, JenniferNewly discovered skeletons of the Early Triassic basal cynodont, Galesaurus planiceps, has enabled a detailed morphological redescription of the postcrania of this genus. The examination of Galesaurus reveals two distinct morphs, namely a gracile and a robust morph. The primary differences between each morph lie in the pectoral and pelvic girdles with further subtle differences in the fore- and hind limbs. The morphological differences between the two morphs may be attributed to ontogeny, sexual dimorphism or the presence of two subspecies. The morphology and high cortical thickness in the limb bones of Galesaurus indicates that it was a more robust animal compared to its closely related sister taxon Thrinaxodon liorhinus. Galesaurus was thus, capable of being an active burrower and may have used burrows to escape the harsh environmental conditions of the Early Triassic. The bone microstructure of Galesaurus reveals uninterrupted fibro-lamellar bone, indicating fast continuous initial grow th, with a change to lamellar-zonal bone, indicating a decrease in growth rate. T he presence of annuli and LAGs in the peripheral lamellar-zonal bone indicates interrupted slow growth and suggests that Galesaurus may have been susceptible to environmental fluctuations. The growth patterns of Galesaurus and Thrinaxodon are similar, but can be distinguished from one another by the presence of lamellar-zonal bone in the former and parallel-fibred bone in the la tter genus. Annuli and LAGs are absent in Thrinaxodon , implying that Thrinaxodon was less susceptible to environmental fluctuations than Galesaurus, as growth did not decrease or cease periodically. Abstract iv Galesaurus, with a short biostratigraphic range from the Palingkloof Member, Balfour Formation and lowermost Katberg Formation of the Lystrosaurus Assemblage Zone, was previously known only from cranial and poorly preserved, isolated postcranial fragments. In contrast, extensive research has been conducted on the more abundant better-known Thrinaxodon, which has a biostratigraphic range that extends the entire Lystrosaurus Assemblage Zone. It was previously assumed that the postcr anial skeletons of basal cynodonts were indistinguishable. However, this study has revealed morphological differences between Galesaurus and Thrinaxodon , allowing the taxa to be distinguished in the absence of cranial material. Examining postcranial material previously identified as Thrinaxodon and ensuring that collection material has been correctly identified can now test the short stratigraphic range of Galesaurus .