Theses and Dissertations at Montana State University (MSU)
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Item A forest entombed in ice: a unique record of mid-Holocene climate and ecosystem change in the northern Rocky Mountains, USA(Montana State University - Bozeman, College of Letters & Science, 2022) Stahle, Daniel Kent; Chairperson, Graduate Committee: David McWethy; This is a manuscript style paper that includes co-authored chapters.Across the high alpine of the northern Rocky Mountains small vestiges of perennial ice have endured for thousands of years. These ice patches reside hundreds of meters above modern treeline, with some persisting through mid-Holocene warmth and others establishing at the onset of a cooler period that began around 5,000-5,500 years BP. Recent warming-driven melting at the margins of one ice patch high on the Beartooth Plateau of northern Wyoming exposed over 30 intact mature whitebark pine (Pinus albicaulis) tree boles, all > 25 cm in diameter. We extracted cross-sectional samples from the stems of 27 preserved logs, and radiocarbon dated annual growth rings from 11 of these trees, anchoring the chronology to a date range spanning 5,947 to 5,436 years BP + or - 51.3 years. From this fossil wood chronology, we developed estimates of warm-season, annual, and biennial average temperatures for upper-elevation treeline during the mid-Holocene. To identify the predominant climate-growth relationships of the subfossil trees, we sampled live whitebark pine trees growing at an adjacent treeline site approximately 120 m lower in elevation. Temperature was found to be the major driver of variability in tree growth at the modern treeline location, with trees producing narrower (wider) rings during periods of cooler (warmer) growing season temperatures. Using linear and non-linear transfer functions based upon the stable statistical relationship between modern tree growth and temperature, we reconstructed past temperature estimates from the ice patch subfossil ring-width chronology. Our results provide estimates of mid-Holocene warm-season (and biennial) average temperatures ranging from 5.7-6.5 °C (-0.44-0.26 °C) respectively. A multi-century regional cooling trend beginning around 5,650 years BP resulted in average temperatures declining below a warm-season (biennial) critical threshold of ~5.8 °C (-0.34 °C), likely leading to the eventual death of the whitebark pine stand and subsequent formation of the ice-patch. This high-quality paleo-ecological dataset reveals a major shift in the alpine and forest ecotone on the Beartooth Plateau following the mid-Holocene warm period and offers further insight on the thermal limits of whitebark pine trees in the Greater Yellowstone Ecosystem.Item Understanding the Coprophilous fungus Sporormiella as a proxy for megaherbivores(Montana State University - Bozeman, College of Letters & Science, 2020) Ulrich, Barbara Carol; Chairperson, Graduate Committee: Cathy WhitlockIn many studies, the presence of the coprophilous fungus Sporormiella in Quaternary sediments has been interpreted as evidence of past megaherbivore activity. Despite its use as an ecological proxy, little is known about the taxonomy and life history of Sporormiella, and the taphonomic processes that lead to its preservation in lake sediments. This information underlies its utility to interpret past herbivore presence and abundance. Present-day bison (Bison bison) dung from Yellowstone National Park was examined to explore the production, dispersal, transportation, deposition, and preservation of Sporormiella there. While Sporormiella was found in dung samples, sediments from two lakes frequently visited by bison failed to yield Sporormiella spores. Laboratory preparation techniques were modified to increase the likelihood of Sporormiella spore survival, yet no spores were identified with the new treatment. Although the occurrence of spores in lake-sediment samples may indicate herbivore presence, our study suggests that spore absence does not necessarily indicate an absence of herbivores. We attribute the absence of spores in sediments to local climatic and seasonal factors that may affect production and transport in the watershed, sedimentary processes that may destroy spores after deposition, and harsh laboratory processing techniques that may damage or destroy spores. More research remains to be done to evaluate the importance of these factors before using Sporormiella as a reliable proxy of herbivore activity.Item Paleoecological utility of feeding traces at Egg Mountain, a rich terrestrial vertebrate locality of the upper Cretaceous Two Medicine Formation, Montana, U.S.A.(Montana State University - Bozeman, College of Letters & Science, 2020) Freimuth, William James; Chairperson, Graduate Committee: David Varricchio; David J. Varricchio, Alexandria L. Brannick, Lucas N. Weaver and Gregory P. Wilson were co-authors of the article, 'Mammal-bearing regurgitalites potentially attributable to Troodon formosus at the Egg Mountain locality, upper Cretaceous Two Medicine Formation, Montana, U.S.A.' submitted to the journal 'PLOS ONE' which is contained within this thesis.; David J. Varricchio, Karen Chin and Sara E. Oser were co-authors of the article, 'Paleoecological implications of invertebrate fecal pellets (Edaphichnium) at a rich terrestrial vertebrate locality, upper Cretaceous Two Medicine Formation, Montana, USA.' submitted to the journal 'Journal of paleontology' which is contained within this thesis.The Egg Mountain locality is a rich terrestrial vertebrate site from the Upper Cretaceous Two Medicine Formation of Montana. Numerous skeletal remains and nesting and dwelling traces of insects and other invertebrates, mammals, lizards, and carnivorous and herbivorous dinosaurs are known from the locality. Despite the diversity of different taxa and behaviors represented, little is known about their respective ecologies. To address this, I investigate a series of feeding traces, including regurgitalites (fossil gastric pellets) and invertebrate fecal pellets, and assess their potential trace-makers and paleoecological and paleoenvironmental implications for the site. Two amalgams of the metatherian Alphadon halleyi are identified as regurgitalites based on the presence of multiple individuals in a confined area, an abundance of paired and indigestible tooth-bearing cranial elements, extensive breakage and disarticulation, and periosteal corrosion patterns attributable to digestion. These are the first mammal-bearing regurgitalites from the Mesozoic. A third amalgam is composed of the multituberculate Filikomys primaevus and is represented by crushed skulls and abundant articulated postcrania, suggestive of a non-predatory origin. The available evidence favors Troodon formosus as the regurgitalite producer. The similar taphonomic features of these regurgitalites and the prey in regurgitates of diurnal raptors suggest Troodon may have manipulated prey during feeding. The ability to egest pellets in a large-bodied, non-volant troodontid supports previous hypotheses that avian-style pellet egestion may have evolved to accommodate increased physiological processes leading to modern birds. A series of unusual peloidal structures are interpreted as invertebrate fecal pellets and resemble the pellet-filled burrow trace Edaphichnium isp. Three morphotypes are identified, including linearly-arranged pellets, pellets in condensed masses, and pellets in dispersed masses. Potential trace-makers include coleopterans, millipedes, and possibly earthworms. The abundance of Edaphichnium isp. and other traces at specific horizons throughout the locality suggest buildup of organic material in the substrate, likely induced by depositional hiatuses. Some Edaphichnium isp. are associated with Maiasaura egg clutches, suggesting invertebrate communities scavenged the decaying nest materials. Taken together, these studies provide ecological and depositional context to the abundance of dinosaur nesting and the diversity of taxa and behaviors represented at the Egg Mountain locality.Item Disentangling anthropogenic and natural drivers of change in vegetation and fire history along the forest-grassland ecotones of the central United States and Patagonia(Montana State University - Bozeman, College of Letters & Science, 2020) Nanavati, William Parashar; Chairperson, Graduate Committee: Cathy Whitlock; Eric C. Grimm was a co-author of the article, 'Humans, fire, and ecology in the southern Missouri Ozarks' in the journal 'The holocene' which is contained within this dissertation.; Cathy Whitlock, Valeria Outes and Gustavo Villarosa were co-authors of the article, 'A holocene history of Araucaria araucana in northernmost Patagonia' submitted to the journal 'Journal of biogeography' which is contained within this dissertation.; Cathy Whitlock, Virginia Iglesias and Maria Eugenia de Porras were co-authors of the article, 'Postglacial vegetation, fire, and climate history along the eastern Andes, Argentina and Chile (lat. 41-55°S)' in the journal 'Quaternary science reviews' which is contained within this dissertation.Disentangling anthropogenic and natural drivers of vegetation and fire history at different spatiotemporal scales is a fundamental challenge in Earth Systems science. To better understand the role of past human ignition in altering long-term ecosystem dynamics, we rely on the anthropogenic fire regime conceptual model proposed by Guyette et al. (2002) in the central U.S. Ozarks. The synthesis of new and existing pollen and charcoal records, and their integration with archaeological, ethnographic, and independent paleoclimate records is used to test the anthropogenic fire regime conceptual model at a longer time scale in the central U.S. Ozarks. Following its validation, this conceptual model is applied to the forest-steppe ecotone east of the Patagonian Andes (38-55°S) for the first time. Although it is well established that Patagonian vegetation and fire history for most of the postglacial period was governed by the strength and position of the Southern Westerly Wind (SWW) storm tracks, the influence of land use since the arrival of American Indians to the region ~12,000 years ago remains unclear. From the late glacial to early Holocene, region-wide increases in fire were associated with aridity while the SWW were weakened and south of their present position. Between ~7000-4000 cal yr BP, increased arboreal taxa and decreased fire throughout Patagonia suggest wet conditions as the SWW moved northward to their present position. After ~4000 cal yr BP, a combination of increased land use and greater climate variability, led to spatially heterogeneous but generally rising fire activity along the forest-steppe ecotone. When trends in the vegetation and fire history of individual sites are compared to each other and to the archaeological record, however, it becomes apparent that American Indians may have served as an important source of ignition, locally increasing landscape heterogeneity since their arrival. During the last 100 years, increased Euro-American settlement and land clearance in Patagonia led to native forest loss, more disturbance, and the spread of introduced taxa along the eastern flanks of the Andes. These ecological changes in the recent century far outweigh thousands of years of American Indian influence on fire and vegetation history.Item Ontogeny and sexual dimorphism in Champsosaurs (Diapsida, Choristodera)(Montana State University - Bozeman, College of Letters & Science, 1997) Katsura, YoshihiroItem Pellet and scat analysis as indicators of past and present habitats(Montana State University - Bozeman, College of Letters & Science, 2000) Craighead, April Charmaine H.Item Comparative taphonomy and paleoecological reconstruction of two microvertebrate accumulations from the late Cretaceous (Maastrichtian) Hell Creek Formation, eastern Montana(Montana State University - Bozeman, College of Letters & Science, 2006) Wilson, Laura Elizabeth; Chairperson, Graduate Committee: John R. HornerAlthough microvertebrate accumulations are commonly used for paleoecological reconstructions, the taphonomic processes affecting the final taxonomic composition of an accumulation are often ignored. To explore the correlation between taphonomic processes and taxonomic structure, one floodplain and one channel-lag deposit from the Maastrichtian Hell Creek Formation were compared. Specimens were quarried to collect high-resolution vertical and horizontal distribution data. Distribution of skeletal elements with specific physical attributes and relative abundance of taxa are shown to correlate with the hydraulic indicators (i.e., grain size, sedimentary structures) of the depositional facies. Conor's Microsite (CM) is located within a laminated sandstone, siltstone, and mudstone facies interpreted as a fluvial overbank deposit. Just Past Celeste Microsite (JPC) is located in a massive sandstone facies and is interpreted as a channel lag deposit. Relative abundance data in conjunction with statistical test results show size, shape, abrasion, and taxonomic compositions to vary significantly between assemblages. Chisquared tests and Correspondence Analyses of CM and JPC data sets indicate significant differences between taxonomic compositions.Item Paleoecology and taphonomy of the Willow Tank Formation (Albian), Southern Nevada(Montana State University - Bozeman, College of Letters & Science, 2008) Bonde, Joshua William; Chairperson, Graduate Committee: David VarricchioThis study documents fossil remains from the Willow Tank Formation and places those remains into a taphonomic and sedimentological context in order to determine the paleoecology of southern Nevada during the Early Cretaceous (Albian). Recovered taxa include Lepisosteidae, Ceratodus, Holostean A, Naomichelys, Baenidae, c.f. Adocus, possible Trionychidae, Crocodyliformes, Thyreophora, Iguanodontia, Titanosauriformes, Tyrannosauroidea, Dromaeosauridae, indet. Theropoda, and two fern morphotypes. Sedimentology of the fossiliferous unit of the Willow Tank Formation suggests these taxa were deposited in an anastomosed fluvial system. Interpretation of an anastomosed fluvial system is based in part upon an overwhelming abundance of overbank fines, single storied channel fills, lack of lateral accretion structures, and common crevasse splay sandstones. Observed paleosols commonly contain carbonate nodules associated with mottled red-green mudrocks. The carbonate nodules are consistent with as seasonally arid environment and reddening of beds may suggest a well drained floodplain. Taphonomic modes include microsite, subaqueous bonebed, subaerial bonebed, and channel fill assemblages. Vertebrate fossils are found predominantly in overbank settings. The fauna of the Willow Tank Formation most resembles that of the Cedar Mountain Formation. Unlike the discrete, temporal, fauna assemblages of the various members of the Cedar Mountain Formation, the Willow Tank Formation fauna contains a mix of these different stratigraphic faunas. One example is the co-occurrence of Early Cretaceous iguanodon-grade and Late Cretaceous hadrosaur-grade teeth. Another example being the presence of a tyrannosauroid tooth in Albian beds of the Willow Tank Formation, where tyrannosauroids are not found in the Cedar Mountain Formation until the Cenomanian. Therefore, Willow Tank Formation strata may shed light on biogeographic and evolutionary relationships at the Early-Late Cretaceous boundary.Item Forest disturbance history in the Sawtooth Mountains of Central Idaho and the Beaverhead Range of Western Montana(Montana State University - Bozeman, College of Letters & Science, 2008) Gage, Joshua Albert; Chairperson, Graduate Committee: Cathy WhitlockStudies of disturbance history are important because they provide a framework for understanding the ecological response to past, present, and future climate change, and this information is useful for paleoecological researchers and land-use managers. Fire and insect outbreaks are common occurrences in western forests, and three studies were undertaken to increase our knowledge of their history in the northern Rocky Mountains. In the first study, sediment cores were sampled from 21 lakes located in forests experiencing mountain pine beetle infestation in the Sawtooth Mountains, Idaho. Cores were analyzed to determine whether or not mountain pine beetle remains were accumulating in the lake sediments in association with recent outbreaks. The study found that insect remains were sparse in the lake sediments, even in sites surrounded by heavily infested forests. These results cast doubt on whether paleo-beetle records can be reconstructed from lake-sediment cores. In the second study, one-meter-long sediment cores were taken from three lakes in Pinus contorta forests in the Sawtooth Mountains, Idaho, to reconstruct a historical record of fire spanning the last 2000 years. High-resolution charcoal analysis of the cores indicated changes in fire activity, but there was not a significant difference in fire occurrence during the relatively dry Medieval Climate Anomaly (1050 - 650 cal yr BP), the cooler Little Ice Age (750 - -50 cal yr BP), and the present day. Results suggest that the current fire regime has persisted for at least 2000 years, with little modification by humans or climate. In the third study, a high-resolution charcoal record was analyzed from Reservoir Lake in the Beaverhead Mountains, Montana to reconstruct the fire history of the last 15,000 years at the lower forest-steppe boundary. The charcoal record indicates relatively low fire frequency between 13,500 cal yr BP and 6000 cal yr BP and increased fire activity from 6000 to 1500 cal yr BP, suggesting increasing aridity in the middle and late Holocene. The fire-climate linkages observed in the paleoecological record provide insights that are useful in understanding future fire regimes with projected climate changes.