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- Butler, Aodhán D., 1986-
(author)
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Exceptionally Preserved Cambrian Lophotrochozoa : Taxonomy, Systematics and Taphonomy of Chengjiang and Indian Springs Lophophorates
- 2014
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Licentiate thesis (other academic/artistic)abstract
- The origin and evolution of Lophotrochozoa can be traced to the plethora of lower Cambrian scleritome taxa. We aim to determine the character suites linking these stem-Lophotrochozoa to their extant crown relatives, in particular the small shelly tommotiids and the stem-group brachiopods. Tracing the origin of morphological characters from these fossils informs the evolution and construction of lophotrochozoan body plans associated with the Cambrian Explosion. This is achieved by comparing records of exceptional preservation, most conspicuously Burgess Shale type Lagerstätten with more widespread Cambrian stem-brachiopods and small shelly fossils with their purported extant relatives, for example. Determining morphological character homologies is crucial to reconstructing the brachiopod stem-group and in polarising character changes associated with the putative transition from scleritome organisms to crown-group brachiopods. In this thesis arguments for a common origin of specific shell structures and exceptionally preserved soft-tissues are investigated. New records of enigmatic stem-group lophotrochozoans are described from two localities, the Indian Springs and Chengjiang Lagerstätte. Comprising the stem-brachiopod Mickwitzia cf. occidens, a putative stem-group entoproct Cotyledion tylodes and an enigmatic agglutinated tubular lophophorate possessing an unusual combination of phoronid, brachiopod and tommotiid characters, Yuganotheca elegans gen. et sp. nov. The interplay of bauplan, microbial activity and environmental factors resulting in such incidences of exceptional soft tissue preservation is also examined critically. Consequently, the evolution of through-gut bearing bilaterians is suggested as the reason for why the Cambrian hosts such a plethora of Lagerstätten. The closure of this taphonomic window is then associated with increased bioturbation following the Cambrian substrate revolution.
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| 2. |
- Claybourn, Thomas, 1989-
(author)
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Cambrian Series 2 (Stages 3-4) Small Shelly Fossils from East Antarctica
- 2017
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Licentiate thesis (other academic/artistic)abstract
- An assemblage of Cambrian Series 2, Stages 3-4 small shelly fossils has been recovered from the Shackleton Limestone and Holyoake Formations of East Antarctica. Small shelly fossils from the early Cambrian are an important window into the world of Cambrian palaeobiology, biostratigraphy and biogeography. The aim of this thesis is to add this view the previously under-described fauna from East Antarctica. The molluscs from the Shackleton Limestone prove important in biostratigraphic correlation to South Australia, North-East Greenland, North China and South China. Morphometric analysis of these has also yielded insights into inter- and intraspecific variation in the helcionelloid mollusc Mackinnonia. The remaining fauna contains certain key taxa for biostratigraphic comparison, such as the tommotiid Dailyatia odyssei, the bradoriid arthropod Spinospitella coronata and the brachiopod Karathele yokensis. This allows for direct correlation with the Cambrian Series 2 Stages 3-4 Dailyatia odyssei Zone of South Australia, further strengthening an already recognised close relationship between the faunas of East Antarctica and South Australia.
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| 3. |
- Bassett-Butt, Lewis, 1990-
(author)
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The Cambrian lophotrochozoans of the Transantarctic Mountains, Antarctica
- 2015
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Licentiate thesis (other academic/artistic)abstract
- The origin of many lophotrochozoan groups can be traced to “small shelly fossil” (SSF) faunas of the Early Cambrian. Antarctica is a key region of study, due to the continent’s known close geographical proximity to well-studied Australian and Indian basins in in the Cambrian. Few studies have focused on this region however, due to a paucity of data. Re-examination of camenellan sclerites from the Early Cambrian Shackleton Limestone of the Churchill Mountains of Antarctica has revealed a previously unidentified species of Dailyatia in the formation, co-occurring alongside previously described Dailyatia odyssei Evans and Rowell, 1990, as in the Arrowie Basin of Australia. Re-examination of material previously described as Kennardia sp. A and Kennardia sp. B has indicated that these taxa can likely be synonymized as a second species of Dailyatia. Dailyatia sclerites were also found in the temporally equivalent “Schneider Hills Limestone” formation, which cropsout in the Argentina Range of Antarctica. These specimens appear to belongto a third species of Dailyatia, suggesting that the spatial distribution of tommotiids in the Early Cambrian was more complex than previously recognized, and that the group may be useful in future biostratigraphic studies. A study ofthe Middle Cambrian (Drumian Stage) Nelson Limestone Formation of the Neptune Range, Antarctica has revealed a moderately diverse brachiopod and trilobite fauna. The brachiopods have strong faunal links to taxa from South Australia and India, as well as other parts of the Antarctic province, fitting independent strong evidence for a united East Gondwanan region in the Middle Cambrian. An unidentified camenellan tommotiid sclerite is also described from the Nelson Limestone. This extends the worldwide temporal range of the tommotiid clade into the Drumian Stage, and suggests that more basal members of the brachiopod stem-group survived to form part of a more diverse Middle Cambrian fauna.
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