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Ammonoids were collected from the Chainman Formation (Mississippian) of southeastern Nevada and southwestern Utah, the Phosphoria Formation (Permian) of southeastern Idaho and westernmost Wyoming, and the Thaynes Formation (Triassic) of northeastern Nevada and southeastern Idaho. The collections are interpreted to represent unwinnowed, untransported death assemblages of ammonoids which were subject to chemical conditions of the nekto-benthic environment. Associated lithologies were sampled and geochemically analyzed for content of phosphate and organic matter. Ammonoid fossil collections, combined with ammonoids ilustrated in the literature, were subjected to the graphical W and D analysis of Raup (1967). The basic parameteres involved in the description of shell-coiling geometry are whorl expansion rate, W, and the distance of the generating curve from the axis of coiling of the shell, D. Values of W determined range from 1.32 to 3.96, which correspond to slight and rapid increases in whorl height during coiling. Values of D determined range from 0.02 to 0.55, which correspond to extremes of involute and evolute coiling· geometries, respectively. Body chamber length corresponds with shell coiling geometry. Values determined in this study range from 10° to 540°. Corresponding W values are 3.96 and 1.50, whereas corresponding D values are 0.02 and 0.40, respectively. Average body chamber length in analyzed ammonoids is observed to decrease from 297° to 209° from Mississippian to Triassic time. Increase in apertural area accompanied this trend, and a possible consequence was that a greater range of prey sizes was afforded ammonoids with shorter body chambers. Life-orientation, described as the angle between the apertural plane and the gravitational vector, is calculated entirely on shell form and other geometrical considerations. Recent observations concerning Nautilus, combined with fossil evidence of epizoan encrustation suggest that ammonoids had an ability to control orientation, which is not observed from preservable morphology. From Mississippian to Triassic time, no trends in reconstructed life-orientation can be substantiated, based solely on Wand D values. Rotational stability during directed locomotion is important for conservation of the energy budget of this nektonic carnivorous organ­ ism. This property is calculated by the distance between the center of buoyancy and the center of gravity of the ammonoid. Values deter­ mined range from .04 (very unstable) to .16 (very stable). Corres­ ponding W values are 1.50 and 4.00 where corresponding D values are 0.20 and 0.02, respectively. A trend toward increasing average rota­tional stability (.07 to .10) is noted for amrnonoids from Mississippian to Triassic time. Efficiency in the utilization of calcium carbonate is the ratio of internal volume of the shell to volume of shell material. Values determined range from 5.80 to 7.25. Corresponding W values are 4.00 and 1.50, corresponding D values are 0.02 and 0.54, respectively. Abundant ammonoids found in black, phosphatic limestones rich in organic matter have an average efficiency value of 6.2. Abundant ammonoids from corresponding light-colored crystalline carbonates have an average efficiency value of 6.02, and indicate no correlation between effi­ciency and abundance. Size-frequency distributions are utilized in recognition of oppor­tunistic species of ammonoids. High numerical abundance, high mortality rate of juveniles, small size and conservation of calcium carbonate typifies the paleo-opportunistic species Cravenoceras, Psuedogastrio­ceras and Ophiceras. Biovolume-relative abundance distributions are useful in discerning the carrying capacity of the habitat both in number of individuals and species diversity. A large area under the biovolume-relative abun­dance profile indicates diversification under optimum environmental conditions; a small area under the profile indicates colonization of a stressful habitat. The Chainman, Phosphoria and Thaynes (Columbites Zone) Formations have ammonoid assemblages which show small areas under the biovolume-relative abundance profile, characteristic of anoxic environmental stress. The Permian stratigraphic units correlative with the Phosphoria Formation have ammonoid assemblages which show large areas under the profile and the associated lithologies, i.e., light­ gray,crystalline carbonates, suggest environments which could support a diversified ammonoid fauna, including large-sized species. Ontogenetic variation produces changes in the body chamber length, life orientation, rotational stability, and utilization of calcium carbonate of the analyzed genera of ammonoids. These ontogenetic variations usually resulted in the development of more involute shell-coiling geometries. Corresponding size-frequency distributions suggest increased mortality rates during ontogeny for some genera (Paracravenoceras, Medlicottia) which show decreasing efficiency in the utilization of calcium carbonate. (182 pages)

Heteromorph ammonites and dinoflagellate cysts from the Upper Cretaceous Northumberland Formation on Hornby Island, British Columbia, Canada are examined. The collection and preparation of new material has enabled the recognition of eleven species of which only three have been reported from the locality. Of these taxa represented from three heteromorph ammonite families in the study area, five are new occurrences and three are new to science. This expansion of the Hornby Island ammonite fauna is presented alongside a pioneering taxonomic survey of dinoflagellate cysts from the same rocks. Together, these macro- and microfossils reinforce a late Campanian age for the Northumberland Formation with the upper extent of the section approaching the Campanian-Maastrichtian boundary (CMB) interval. The palaeoecology and evolutionary relationships of these heteromorph ammonoids are considered with new insights into their ontogenetic development and neritic palaeoenvironmental circumstances. The dinoflagellate cysts and associated terrestrial palynomorphs have also allowed for enhanced palaeoenvironmental reconstruction and depositional setting inference. The scope of the studied material, and the presence of key index taxa, enables refined biostratigraphy and a stronger basis for correlation of the Hornby Island succession with neighboring coeval biotic provinces. / Graduate / 2018-08-10