Many trilobites have cuesta-like structures, known as terrace ridges, on both the dorsal and ventral surfaces of the exoskeleton. Although terrace ridges all appear to have the same basic construction, they are highly variable and several types are known. These structures are poorly understood and there are many, varied and sometimes contradictory theories as to their function, which are discussed herein. Terrace ridge shape variation was explored across Class Trilobita, first qualitatively and then using a novel geometric morphometric technique, extended (landmarkregistered) eigenshape analysis (EEA) (MacLeod, 1999). A database containing details of over 6000 images of trilobite terrace ridges in the literature was compiled from over 450 scientific papers, from which a resource of 1600 scanned images of terrace ridges within the Asaphida was produced. A successful heuristic analysis technique was developed using EEA, analysing approximately 400 of these images. Trends in the variation of simplified terrace ridge arrays on several parts of the trilobite were successfully identified. The analysis of these terrace ridge arraysachieved good taxonomic separation and, in particular, this analysis appeared to separate pelagic and benthic terrace ridge-bearing forms, potentially providing an independent cryptic test for trilobite mode of life hypotheses based on exposed morphologies. Both qualitative and quantitative strands of research contributed to a phylogenetic discussion of terrace ridges across Class Trilobita as well as informing an analysis of the suggested functions of terrace ridges. The mapping of terrace ridge character states clarified patterns of acquisition and secondary loss of terrace ridges across the Class. Secondary losses were suggested to be related to the adoption of specialised feeding behaviours and the development of alternative types of sculpture. Some support was found for theories of frictional interaction and species recognition as roles for terrace ridges from the morphometric analyses.

No description available.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2001. / "September 2001." Vita. Page 223 blank. Includes bibliographical references.

Thesis (M.S.)--Joint Program in Oceanography/ Applied Ocean Science and Engineering, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution, 2003. / Includes bibliographical references (p. 768-69).

Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2000. / Includes bibliographical references (leaves 141-151).

Thesis (Ph. D.)--Oregon State University, 2001. / Typescript (photocopy). Includes bibliographical references (leaves 141-151). Also available on the World Wide Web.

Pressured and ridged ice is a dangerous hazard facing ships in the Arctic. Ships can become stuck or beset in these conditions, which is environmentally and economically costly. Understanding where and when ridges form as a result of pressured ice is important for ensuring safe winter shipping operations; however there have been few studies to date regarding the distribution of ridges and their impacts within a geographic region. The Hudson Strait, which connects Hudson Bay and the Atlantic Ocean, is the site of ongoing winter shipping, where vessels frequently encounter pressured ice. This thesis addresses two questions: where and when do ridges occur in the Hudson Strait and what are their impacts on an ice strengthened vessel traveling through the Strait. To answer the first question, ridges were manually identified in RADARSAT-1 and -2 images during the winter months (December to May) from 1997-2012. Ridge counts and densities for each winter season were calculated and their spatial distribution was mapped. A 30-year sea ice climatology of the Hudson Strait was also created in order to understand ongoing trends in freeze-up and breakup timing in the region. Recurring patterns in the location and timing of ridging were found in the Hudson Strait, specifically in areas where shearing and bottlenecks created pressure. Ridge densities were correlated with sea level pressure, air temperature and wind NCEP reanalysis data to look to for connections between these factors and ridge densities. Some connections were found between freeze-up dates, sea level pressure and ridge densities. The second half of this thesis focuses on how ridges impact the voyage of an ice-strengthened vessel. Log books from the MV Arctic, a cargo ship that makes two winter transits through the Hudson Strait every year, were used to plot the movement of the ship and where and when it became beset. These data were examined for temporal and spatial patterns in besetting events. Most besetting events took place in February and March. They typically occurred in the eastern and western ends of the Strait. These voyages were compared to ridge data from the first half of thesis, and there were good correlations between the presence of high ridge densities and ship besetting events, demonstrating that ridge densities identified in satellite imagery can act as a proxy when forecasting hazardous ice conditions. This research fills an important knowledge gap in understanding where and when pressured ice forms in the Hudson Strait and what factors play a role in creating this hazardous ice condition. It also addresses the impacts that ridges have on ship transits through the Strait.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 22, 2010). Appendices are available as supplemental PDF files. Includes bibliographical references (p. 249-263).

Thesis (doctoral)--Johann Wolfgang Goethe Universität, 2004. / Includes bibliographical references (p. [270]-299).