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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Temnospondyl ontogeny and phylogeny, a window into terrestrial ecosystems during the Permian-Triassic mass extinction

McHugh, Julia Beth 01 May 2012 (has links)
Temnospondyls are the most species-rich group of early amphibians, but species-level phylogenetic analyses of this large clade have so far only incompletely sampled the group. This study represents the largest and most comprehensive species-level phylogenetic study of Temnospondyli, sampling 99 taxa for 297 morphological characters from all seven continents through nearly 170 million years of their evolutionary history. Results of this analysis support the monophyly of several clades. Phylogenetic definitions are updated and three new clades names are proposed: Eutemnospondyli, Neostereospondyli, and Latipalata. Major splits within temnospondyl evolution are recovered at the base of Eutemnospondyli (Euskelia and Limnarchia) and Neostereospondyli (Capitosauria and Trematosauria). Archegosauriodea is recovered within Euskelia. Dendrerpeton is recovered as the immediate sister taxon of Dissorophoidea, not Eryopoidea. This arrangement suggests that for subclade-level analyses of dissorophoids, which bear on the `Temnospondyl Hypothesis' for a putative origin of Lissamphibia within dissorophoids, the convention of rooting on Dendrerpeton and including eyropoids in the ingroup should be re-evaluated in light of the new temnospondyl topology. Study of the tempo and mode of evolution within temnospondyl amphibians has been limited in the past by the availability of a clade-wide, species-level phylogenetic analysis. The phylogenetic dataset generated by this study has allowed for investigation into rates of origination and extinction amongst this long-lived group at a scale not previously available for exploration. Extinction rate and origination rate, when calculated strictly from stratigraphic data, showed a high correlation with the number of sampled localities, indicating a strong influence on this evolutionary signal by sampling and rock record biases. But when rates were augmented with phylogenetic data, four periods of increased lineage origination are discernible from the Pennsylvanian to the Early Triassic. The largest of these origination events coincides with the Permo-Triassic mass extinction, indicating that amphibians were taking advantage of favorable conditions during the largest biological crisis in the Phanerozoic record. Temnospondyl amphibians are the second most abundant fossil vertebrates in the Permo-Triassic Karoo Basin of South Africa. Paleohistological investigation of these amphibians was hampered by small sample size and taxa available for sampling. Incorporation of paleohistologic data from other analyses helped to alleviate this problem; however, Temnospondyli remains under sampled in paleohistological analyses. Results show cyclic growth and a lifespan of thirty years or more in basal stereospondyls, convergence to sustained, non-cyclic growth in terrestrial temnospondyls, support findings based on gross morphology that Lydekkerina is a terrestrial stereospondyl, and suggest that ribs are a viable source of skeletochronologic information in temnospondyls and should serve as preferred material when proximal limb diaphyses are not available. Sustained, azonal growth in Micropholis is unlike that of Apateon or extant caudatans, suggesting a possible adaptation to local conditions in the earliest Triassic of Gondwana.
2

Three-dimensional Virtual Histology of Early Vertebrate Scales Revealed by Synchrotron X-ray Phase-contrast Microtomography

Qu, Qingming January 2015 (has links)
Vertebrate hard tissues first appeared in the dermal skeletons of early jawless vertebrates (ostracoderms) and were further modified in the earliest jawed vertebrates. Fortunately, histological information is usually preserved in these early vertebrate fossils and has thus been studied for more than a century, done so by examining thin sections, which provide general information about the specific features of vertebrate hard tissues in their earliest forms. Recent progress in synchrotron X-ray microtomography technology has caused a revolution in imaging methods used to study the dermal skeletons of early vertebrates. Virtual thin sections obtained in this manner can be used to reconstruct the internal structures of dermal skeletons in three-dimensions (3D), such as vasculature, buried odontodes (tooth-like unites) and osteocytes. Several body scales of early vertebrates have been examined using this imaging method and in situ 3D models of internal structures are created. Andreolepis (an early osteichthyan) scale shows linear growth pattern of odontodes in early developmental stage, which is not observable in traditional thin sections. The scale of another early osteichthyan Psarolepis was studied in the same way. Comparison between Andreolepis and Psarolepis shows that cosmine, a tissue complex in dermal skeleton of early sarcopterygians, originated by a developmental change of odontode shape. Two scales of osteostracans, a group of extinct jawless vertebrates, were studied in 3D and more details have been revealed in comparison to previous results based solely on 2D thin sections. 3D data enables us to compare the vasculature and canal system in different taxa in great detail, which forms the basis of formulating primary homology hypothesis and phylogenetic characters. The new data resulting from this study suggests that vertebrate fossils have preserved much more histological information than we currently appreciate, and provide a new data source of microanatomical structures inside the fossils that can contribute new characters for phylogenetic analysis of early jawed vertebrates.
3

Descrição osteo-histológica de elementos fósseis de Dinodontosaurus turpior (Therapsida, Dicynodontia), Mesotriássico do Rio Grande do Sul, Brasil

Bueno, Ana de Oliveira January 2015 (has links)
Estudos relacionados à microestrutura óssea de elementos fósseis surgiram no século XVIII, porém começaram a desenvolver-se mais profundamente somente nas últimas décadas. Hoje, a Paleohistologia é uma das áreas mais promissoras dentro da Paleontologia, pois nos possibilita acessar uma série de características do espécime fóssil que complementam nosso conhecimento sobre o animal. Assim como outros clados, os Dicynodontia vêm sendo estudados por esse viés há muito tempo, e hoje conhecemos os padrões ósseos e de crescimento de um grande número de espécies. A presente dissertação traz a descrição ósteo-histológica de alguns elementos fósseis de Dinodontosaurus turpior, uma espécie de dicinodonte de grande porte do Mesotriássico, encontrada em afloramentos da Formação Santa Maria. Os ossos analisados apresentam majoritariamente uma matriz do tipo fibrolamelar, com alguns subtipos da matriz em dois fragmentos, ausência de linhas de crescimento nos espécimes juvenis e presença destas em fragmentos de espécimes adultos, possibilidade de EFS em um fragmento de adulto, reconstrução secundária surgindo apenas em estágios mais avançados e córtex razoavelmente espesso. Tais características não divergem do padrão já descrito para o grupo como um todo, cujas interpretações para a biologia do animal incluem um metabolismo mais acelerado e uma rápida osteogênese, quando comparada com a de terápsidos mais basais. / Studies related to bone microstructure of fossil elements started about the 18th century, however, they began to significantly grow only in the past few decades. Today, paleohistology is one of the most promising areas inside paleontology, because permits to access several characteristics of the fossil specimen which complement our knowledge about the animal. As in other clades, Dicynodontia has been studied in this subject for long time, and now we know about bone growth and microstructure patterns in a variety of species. The present study shows a osteohistological description of some fossil elements of Dinodontosaurus turpior, a medium-to-large size dicynodont species from Middle Triassic of Rio Grande do Sul, Brazil, founded in outcrops of the Santa Maria Formation. The bones analyzed present a fibrolamelar type of bone tissue as major matrix, with some subtypes appearing in a couple of fragments. Growth lines are absent in all juvenile fragments, but appears in the adult ones. One of the adult fragments seems to have an EFS. Also, it was observed secondary reconstruction in adult sample and a thick cortex in all slides that RBT can be calculated. All these features were already been observed in the Dicynodontia clade, whose biological interpretations include an accelerated metabolism and rapid osteogenesis, when compared with basal therapsids.
4

Descrição osteo-histológica de elementos fósseis de Dinodontosaurus turpior (Therapsida, Dicynodontia), Mesotriássico do Rio Grande do Sul, Brasil

Bueno, Ana de Oliveira January 2015 (has links)
Estudos relacionados à microestrutura óssea de elementos fósseis surgiram no século XVIII, porém começaram a desenvolver-se mais profundamente somente nas últimas décadas. Hoje, a Paleohistologia é uma das áreas mais promissoras dentro da Paleontologia, pois nos possibilita acessar uma série de características do espécime fóssil que complementam nosso conhecimento sobre o animal. Assim como outros clados, os Dicynodontia vêm sendo estudados por esse viés há muito tempo, e hoje conhecemos os padrões ósseos e de crescimento de um grande número de espécies. A presente dissertação traz a descrição ósteo-histológica de alguns elementos fósseis de Dinodontosaurus turpior, uma espécie de dicinodonte de grande porte do Mesotriássico, encontrada em afloramentos da Formação Santa Maria. Os ossos analisados apresentam majoritariamente uma matriz do tipo fibrolamelar, com alguns subtipos da matriz em dois fragmentos, ausência de linhas de crescimento nos espécimes juvenis e presença destas em fragmentos de espécimes adultos, possibilidade de EFS em um fragmento de adulto, reconstrução secundária surgindo apenas em estágios mais avançados e córtex razoavelmente espesso. Tais características não divergem do padrão já descrito para o grupo como um todo, cujas interpretações para a biologia do animal incluem um metabolismo mais acelerado e uma rápida osteogênese, quando comparada com a de terápsidos mais basais. / Studies related to bone microstructure of fossil elements started about the 18th century, however, they began to significantly grow only in the past few decades. Today, paleohistology is one of the most promising areas inside paleontology, because permits to access several characteristics of the fossil specimen which complement our knowledge about the animal. As in other clades, Dicynodontia has been studied in this subject for long time, and now we know about bone growth and microstructure patterns in a variety of species. The present study shows a osteohistological description of some fossil elements of Dinodontosaurus turpior, a medium-to-large size dicynodont species from Middle Triassic of Rio Grande do Sul, Brazil, founded in outcrops of the Santa Maria Formation. The bones analyzed present a fibrolamelar type of bone tissue as major matrix, with some subtypes appearing in a couple of fragments. Growth lines are absent in all juvenile fragments, but appears in the adult ones. One of the adult fragments seems to have an EFS. Also, it was observed secondary reconstruction in adult sample and a thick cortex in all slides that RBT can be calculated. All these features were already been observed in the Dicynodontia clade, whose biological interpretations include an accelerated metabolism and rapid osteogenesis, when compared with basal therapsids.
5

Descrição osteo-histológica de elementos fósseis de Dinodontosaurus turpior (Therapsida, Dicynodontia), Mesotriássico do Rio Grande do Sul, Brasil

Bueno, Ana de Oliveira January 2015 (has links)
Estudos relacionados à microestrutura óssea de elementos fósseis surgiram no século XVIII, porém começaram a desenvolver-se mais profundamente somente nas últimas décadas. Hoje, a Paleohistologia é uma das áreas mais promissoras dentro da Paleontologia, pois nos possibilita acessar uma série de características do espécime fóssil que complementam nosso conhecimento sobre o animal. Assim como outros clados, os Dicynodontia vêm sendo estudados por esse viés há muito tempo, e hoje conhecemos os padrões ósseos e de crescimento de um grande número de espécies. A presente dissertação traz a descrição ósteo-histológica de alguns elementos fósseis de Dinodontosaurus turpior, uma espécie de dicinodonte de grande porte do Mesotriássico, encontrada em afloramentos da Formação Santa Maria. Os ossos analisados apresentam majoritariamente uma matriz do tipo fibrolamelar, com alguns subtipos da matriz em dois fragmentos, ausência de linhas de crescimento nos espécimes juvenis e presença destas em fragmentos de espécimes adultos, possibilidade de EFS em um fragmento de adulto, reconstrução secundária surgindo apenas em estágios mais avançados e córtex razoavelmente espesso. Tais características não divergem do padrão já descrito para o grupo como um todo, cujas interpretações para a biologia do animal incluem um metabolismo mais acelerado e uma rápida osteogênese, quando comparada com a de terápsidos mais basais. / Studies related to bone microstructure of fossil elements started about the 18th century, however, they began to significantly grow only in the past few decades. Today, paleohistology is one of the most promising areas inside paleontology, because permits to access several characteristics of the fossil specimen which complement our knowledge about the animal. As in other clades, Dicynodontia has been studied in this subject for long time, and now we know about bone growth and microstructure patterns in a variety of species. The present study shows a osteohistological description of some fossil elements of Dinodontosaurus turpior, a medium-to-large size dicynodont species from Middle Triassic of Rio Grande do Sul, Brazil, founded in outcrops of the Santa Maria Formation. The bones analyzed present a fibrolamelar type of bone tissue as major matrix, with some subtypes appearing in a couple of fragments. Growth lines are absent in all juvenile fragments, but appears in the adult ones. One of the adult fragments seems to have an EFS. Also, it was observed secondary reconstruction in adult sample and a thick cortex in all slides that RBT can be calculated. All these features were already been observed in the Dicynodontia clade, whose biological interpretations include an accelerated metabolism and rapid osteogenesis, when compared with basal therapsids.
6

Enhanced Resolution of the Paleoenvironmental and Diagenetic Features of the Silurian Brassfield Formation

Oakley, Lisa Marie 25 May 2013 (has links)
No description available.

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