3. Electronic Theses and Dissertations (ETDs) - All submissions

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    Are there order specific patterns of cortical gyrification and if so why?
    (2008-12-10T11:53:58Z) Pillay, Praneshri
    Abstract (for Chapter 2) Objective: The aim was to test the hypothesis that the order is a significant phylogenetic grouping in terms of quantifiable gyrification indices. Method: The gyrification index (GI) was measured from serial sections of the brain of twenty five different mammalian species, representing the different orders i.e. primates, carnivores, artiodactyls and rodents. Image J analysis was used to measure the contours of the cerebral cortex and the GI was calculated using three different methods of analysis i.e. complete vs outer; gyral vs sulcal and outer vs inner surface contours. The measurements were then computed against the brain weights of each species within the order. Results: An increasing GI correlates with an increasing brain weight in all the mammalian orders. Each order has its own specific allometric patterns that are significantly different from the other orders examined. The artiodactyls were the mammals with the most gyrencephalic brains, these species being significantly more gyrencephalic than all other mammals when species of similar brain weights are compared. The North American beaver has an atypically lissencephalic brain for its size, differing from the trend for increased gyrencephaly found in the other rodent species examined. Conclusions: Our results show definite trends and patterns specific to each order. So it would seem that the order is a significant phylogenetic grouping in terms of this neural parameter, from which we can predict with a reasonable degree of certainty, the GI of any species of a particular order, if we know the brain weight. Abstract (for Chapter 3) The mammalian order has proven to be a significant phylogenetic grouping in terms of gyrification from which we can predict with a reasonable degree of certainty, the GI of any species of a particular order, if we know the brain weight. We have attempted in the present study to identify potential causes for gyrification at the class level by investigating relationships at the level of the order. It appears that clues to the extent and pattern of gyrification in the different mammalian orders might be related to the bones that constitute the braincase. The external surface areas of the bones of the cranial vault of seventeen different mammalian species were measured using a microscribe digitiser. These values were plotted against brain weight from which we could then calculate residual values, determining if there was more or less external cranial vault area than expected for the size of the brain. These residuals were then plotted against the gyrification indices determined in a previous study for the species examined. Results indicated that for the primates and artiodactyls the skull may potentially be considered as a limiting factor on the expansion of the cerebral cortex; however, the carnivore and rodent orders show conflicting results which suggest that the relative surface area of the skull appears to have no effect on the quantitative extent of gyrencephaly. These inconclusive findings suggest that causes contributing to the quantitative extent of gyrification across mammals may be multifactorial, and more parameters may need to be included in the analysis to arrive at an answer.
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    Constraints versus adaptations as contending evolutionary explanations of morphological structure : The giraffe (Giraffa Camelopardalis) head and neck as a heuristic model
    (2008-12-01T09:33:58Z) Badlangana, Ludo Nlambiwa
    The current study uses the head and neck of giraffe (Giraffa camelopardalis) as a model for tracking the course of evolutionary change. Gould (2002) has argued that there are three main avenues of evolutionary change that result in the genesis of new morphologies. These are phylogenetic constraints, structural or allometric scaling laws of form, and specific unique adaptations. It is well known that the unique characteristic of the giraffe is its extremely long neck and yet, it only has seven cervical vertebrae. To study the neck the vertebral body lengths of different aged giraffes were measured to determine the contribution of the cervical vertebrae to the total vertebral column. The vertebrae of several extant ungulates as well as those of fossil giraffids were used as a comparison with the giraffe. CT scans were used on several giraffe skulls to study the extent of the frontal sinus in the giraffe in an attempt to explain why the giraffe evolved such a large frontal sinus. The vertebral columns and skulls of several ungulates, including the okapi (Okapia johnstoni) were also used to compare with the results obtained from the giraffe. Immunohistochemistry was used to study the medulla and spinal cord sections of the giraffe to determine if the location and size of the nuclei remained unchanged to the basic ungulate or mammalian plan in spite of the unusually long neck, or if this long neck led to changes in the nuclei found in those regions. The results of these stains were all compared to the published literature available. Although more studies need to be conducted on other ungulates to conclusively determine why giraffe have evolved a long neck, overall the results showed that the anatomy giraffe head and neck remained true to the basic mammalian plan, with very little changing in terms of it morphology. The giraffe brain and spinal cord also resembled that of a typical ungulate. This leads to the conclusion that constraints and allometric scaling laws of form play a greater role than previously thought in the evolution of extreme morphologies.
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    An assessment of phylogenetic origin in Chiroptera using the neuromodulatory system
    (2008-03-11T06:48:32Z) Maseko, Busisiwe Constance
    ABSTRACT The current study documents the findings from immunohistochemical examination of the brains of microbats and megabats (Chiroptera) using antibodies for cholineacetyltransferase (cholinergic neurons), tyrosine hydroxylase (dopaminergic, adrenergic and noradrenergic neurons), and serotonin (serotonergic neurons). The objective of the study was firstly to describe the anatomical organization and morphology of the neuromodulatory systems (nuclear complement) in both microbats and megabats, as there is no literature on these systems in the brains of chiropterans. Secondly, we aimed to investigate whether or not there are differences in these systems between the two suborders of chiroptera in hopes to shed some light on the phylogeny of the two, which is a controversial subject. The two groups were found to possess clear differences in their respective neuromodulatory nuclear complements. The differences observed between the two groups include a dorsal division of the locus coeruleus (A6d), which was absent in microbats but present in megabats, also the absence of an A4 in microbats but clear presence in megabats, and the parabigeminal (PBg) nucleus that was absent in microbats but clearly visible in megabats. The microbats were found to possess a complement that appeared similar to that of insectivores; whereas megabats had a complement resembling that of primates, carnivores and rodents. The differences found between the two groups suggest a diphyletic origin for the two groups.
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    Contributions to the geochronology and geological evolution of the Central African Copperbelt
    (2006-03-23) Rainaud, Christine Claire Laurence
    This thesis presents the results of a broad geochronological investigation into the nature and evolution of the Central African Copperbelt, host of world class Cu-Co deposits in Zambia and the Democratic Republic of Congo. UPb SHRIMP dating of detrital, xenocrystic and magmatic zircons and metamorphic monazite as well as 40Ar-39Ar analyses on biotite, muscovite and microcline constrained the nature and the evolution of the basement, the deposition of the Katangan sedimentary sequence and the provenance of the sediments, and finally the different metamorphic episodes which affected the region. Regarding the pre-Katangan basement, U-Pb SHRIMP analyses of detrital and xenocrystic zircons revealed the first evidence of a cryptic c. 3.2-3.0 Ga Mesoarchaean terrane, named the Likasi terrane, in the basement of the Copperbelt. It was also discovered that the Lufubu schists, previously thought to be sedimentary in origin, are in fact intermediate metavolcanic rocks. These Lufubu schists, together with granitoids and gneisses from Zambia, yielded U-Pb SHRIMP ages between 2050 Ma and 1850 Ma and are interpreted as being related to the evolution of a large magmatic arc (or several magmatic arcs). These Paleoproterozoic terrains define the Lufubu Metamorphic Complex, which evolved together with the Bangweulu Block, the Ubendian Belt and the Tanzanian craton to collide with the Angola-Kasai craton to form the Kibaran Belt during the 1.4-1.0 Ga Kibaran Orogeny. Unconformably overlying the Lufubu Metamorphic Complex is the Muva Group, which is sedimentary in origin. A maximum U-Pb age of 1941 ± 40 Ma was found for its deposition in the Copperbelt area. Concerning the Katanga Supergroup, U-Pb SHRIMP analyses on detrital zircons showed that the sediments are mainly derived by erosion from the Paleaoproterozoic basement. 40Ar-39Ar analyses of detrital muscovites from the Biano Group, which forms the topmost unit of the Katanga Supergroup, yielded a maximum age of deposition of 573 ± 5. This implies a terminal Neoproterozoic and/or early Palaeozoic age for terminal Katangan deposition, and supports previous models for the deposition of the Biano Group in a foreland basin to the Lufilian Orogen . Finally, U-Pb SHRIMP analyses on monazites and 40Ar-39Ar analyses on biotite, muscovite and K-feldspar yielded ages at c. 590, c. 530, c. 512 and a range between 492 and 450 Ma. These ages correspond respectively to various events during and following the Pan-African Damaran-Lufilian- Zambezi orogeny, formed by collision of the Congo and Kalahari cratons, namely to a tectonic event coinciding with subduction-related eclogite facies metamorphism elsewhere in the Lufilian orogen; to the final stage of collision between the Kalahari and Congo cratons; to a wide-spread regional mineralising event; and finally to post-orogenic uplift and regional cooling.
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    The Sub-Kalahari geology and tectronic evolution of the Kalahari basin, Southern Africa
    (2006-02-15) Haddon, Ian Gerald
    Geophysical, borehole and mapped data from the Kalahari Basin were used to create maps of the sub-Kalahari geology, isopachs of the Kalahari Group and basal gravels and a sub-Kalahari topographical surface. These are the first basin-wide maps of this type to be produced. These new data were interpreted with the aid of an extensive literature review as well as data gathered at three localities in the southern part of the Kalahari Basin and enabled several conclusions to be made regarding the tectonic evolution of the area. The sub-Kalahari Geological Map shows that rocks dating from the Archaean to present are exposed on the edges of the basin as well as covered by the Kalahari Group sedimentary rocks. Many of the rocks shown on the sub-Kalahari geological map record a history of rifting and subsequent collision, with the NE and SW trending structures appearing to have been reactivated at various times in the geological past. The extent of Karoo Supergroup rocks is greater than previously thought and Karoo sedimentary and volcanic rocks cover a large percentage of the sub-Kalahari surface. The Karoo Supergroup lithologies have been intruded by dolerite dykes and sills and the massive Botswana Dyke Swarm is shown on the sub-Kalahari map extending in a northwest direction across Botswana. The subtraction of the thicknesses of Kalahari Group sediments from the current topographical digital elevation model (DEM) of Africa in order to prepare a DEM of the sub-Kalahari topographical surface and the preparation of an isopach map of the basal gravels gives some indication of the courses followed by Mid-Cretaceous rivers. Topographic profiles along the proposed courses of these rivers show that the floor of the Kalahari Basin has a particularly low elevation in certain areas suggesting that downwarp of the interior of the basin rather than adjacent uplift was the driving force behind Kalahari Group sedimentation. When down-warp of the Kalahari Basin began in the Late Cretaceous these rivers were back-tilted into the newly formed basin and deposition of the Kalahari Group sediments began. The basal unit of the Kalahari Group consists of gravels deposited by the Cretaceous rivers as well as on scree slopes. As down-warp of the basin continued, so more gravels were deposited as well as the sand and -iifiner sediment carried by the rivers. Thick clay beds accumulated in the lakes that formed by the back-tilted rivers, with sandstone being deposited in braided streams interfingering with the clays and covering them in some areas as the shallow lakes filled up with sediment. During the Mid-Miocene there was a period of tectonic stability that saw the silcretisation and calcretisation of older Kalahari Group lithologies. At the end of the Miocene there was some uplift along the eastern side of southern Africa as well as along certain epeirogenic axes in the interior. In general this uplift was fairly gentle. Later more significant uplift in the Pliocene possibly elevated Kalahari Group and Karoo Supergroup sedimentary rocks above the basin floor and exposed many of them to erosion. The eroded sand was washed into the basin and reworked into dunes during drier periods. This uplift occurred along epeirogenic axes and was greater than the Miocene uplift. The development of the East African Rift System (EARS) in the Late Eocene or Oligocene has had a significant influence on the Kalahari Basin. Reactivation of older NE-SW trends by SWpropagating rifts extending from the main EARS is evident by recent movement along faults along the Damara Belt and those that were associated with Karoo sedimentation and post-Karoo graben formation. The propagating rifts have resulted in uplifting, faulting and in some cases, graben formation. In some cases lakes have formed in the grabens or half-grabens themselves and in other cases they have been formed between the uplifted arches related to parallel rifts. The propagating rifts have had a strong influence on the drainage patterns and shape of the Kalahari Basin, in particular in the middle parts of the basin where they have controlled the formation of the Okavango Delta and the Makgadikgadi pans
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