Theses and Dissertations at Montana State University (MSU)
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Item A mess of rotten eggs from the Two Medicine Formation, Montana(Montana State University - Bozeman, College of Letters & Science, 2024) Tucker, Katherine Lydia; Chairperson, Graduate Committee: David J. VarricchioThe Two Medicine Formation of Montana is known for producing many dinosaur eggs in varying states of preservation. An unusual clutch of eggs MOR 11881 was recently found in the formation that exhibits some distinctive preservation features. The purpose of this research is to describe this clutch using multiple techniques to identify and better understand its taphonomic history. To do this the clutch was prepared by removing sediment from around the eggs, then examined using light microscopy, scanning electron microscopy (SEM), cathodoluminescence (CL), energy dispersive x-ray spectroscopy (EDX), and electron backscatter diffraction analysis (EBSD). Preparation uncovered eleven partially compressed ellipsoidal eggs in the clutch. Microscopy of the eggshell revealed that it is made of two structurally distinct layers. The lower layer at the base of the eggshell is here referred to as the blocky layer based on the blocky texture of the crystals in SEM images. This layer is sometimes interrupted by a phosphatic dark region. The second layer is the lobed layer found along the outer surface of the eggshell. It is characterized by lobes of blocky crystals surrounded by smaller radiating crystals. In addition to the eggshell the eggs also preserve a phosphatized eggshell membrane, two distinct types of pellets, large masses of collophane crystals and hyphae like structures. Unaltered eggshell is found in the sediment surrounding the clutch. The eggshell of the MOR 11881 clutch does not match any described ootaxon but is similar to eggshell found at the Egg Mountain quarry which was never identified. The unusual structure of the eggshell could be the result of multiple stages of alteration. Several structures in the eggshell including the lobes and the dark region are most likely the result of alteration. The presence of unaltered eggshell near the eggs indicates that the source of alteration was the decay of the eggs as recorded by their contents. This decay also produced the conditions necessary for the exceptional preservation of the eggshell membrane.Item Ichnology and sedimentology of the non-marine Frontier Formation (upper Cretaceous) of southwestern Montana(Montana State University - Bozeman, College of Letters & Science, 2023) Panasci, Giulio; Chairperson, Graduate Committee: David J. Varricchio; This is a manuscript style paper that includes co-authored chapters.The Frontier Formation of southwestern Montana (USA) is comprised of rocks assigned to the early Upper Cretaceous (Cenomanian- Santonian), and has recently yielded a notable fossil record, mostly comprised of dinosaur tracks and invertebrate trace fossils. This fossil record lays within a poorly understood period of the Upper Cretaceous, also known as the middle Cretaceous, valued as critical to understand the evolution of terrestrial ecosystems in North America at the end of the Mesozoic Era. This study aims to describe and analyze preservation and distribution of the Frontier trace fossils record. Twelve stratigraphic sections are measured and sedimentology, taphonomy, and stratigraphic framework described for the main fossiliferous sites. Sixty-five dinosaur tracks and associated invertebrate traces are described. Three tracks are further analyzed by combining anatomical characters and track morphological features to infer a more specific producer. Photogrammetry, tridimensional models, and color elevation maps are generated to document significant specimens and to map two excavated track sites. A concise description and classification of a freshwater turtle is also included to enhance paleoecological and paleodepositional reconstructions. A Coniacian age is provided for the Frontier Formation, main fossiliferous sites. Sedimentology and fossil record suggest the establishment of a rich ecosystem in alluvial plains and wetlands extending between the offshoots of the uplifting Rocky Mountains to the east and the Cody Sea to the east. Facies distribution across the southwest-northeast transect suggests that fossil distribution and preservation is mainly controlled by autogenic and allogenic processes seen in foreland basin systems. Tracks and invertebrate trace fossils preservation was likely favored by high sedimentation rates and variations of the ground water table. Dinosaur track assemblage is comparable to those reported in other middle Cretaceous formations of western North America and include derived hadrosauriform ornithopods, ankylosaurians, and theropods. The integration of body fossil data would suggest the presence of a fauna that included elements (i.e. Neurankylus sp.) shared with Campanian and Maastrichtian formations, suggesting that the Coniacian ecosystems across southwestern Montana was likely undergoing a process of provincialisms as seen in North America at the end of the Cretaceous.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 Nest site taphonomy of modern archosaurs(Montana State University - Bozeman, College of Letters & Science, 2016) Ferguson, Ashley Lynn; Chairperson, Graduate Committee: David Varricchio; David J. Varricchio, Carlos I. Piña and Frankie D. Jackson were co-authors of the article, 'From eggs to hatchlings: nest site taphonomy of American crocodile (Crocodylus acutus) and broad snouted caiman (Caiman latirostris)' submitted to the journal 'Palaios' which is contained within this thesis.; David J. Varricchio and Alex J. Ferguson were co-authors of the article, 'Nest site taphonomy of colonial ground nesting birds at Bowdoin National Wildlife Refuge' submitted to the journal 'Palaios' which is contained within this thesis.The goal of this thesis is to investigate the taphonomic processes that affect crocodylian and modern bird nesting localities in the hope that they would shed light into the identification of fossil nesting grounds and the interpretation of juvenile developmental stage. This project in particular observed nests of American crocodiles (Crocodylus acutus) at the Turkey Point Power Plant in Homestead, Florida, broad snouted caiman (Caiman latirostris) nests in the Northern Santa Fe and Chaco Provinces of Argentina, and colonial ground nesting birds (American white pelicans, double-crested cormorants, ring-billed and California gulls) at Bowdoin National Wildlife Refuge (BNWR) east of Malta, Montana. A major component of this project is the documentation of potentially preservable components, i.e., specimens (bones, eggshell, etc.) and structures (e.g. nesting traces) that might be represented in the fossil record. This thesis documents the agents and processes influencing bone and egg accumulations and nesting trace preservation across diverse biologies and environments.Item Osteology, phylogeny, taphonomy, and ontogenetic histology of Oryctodromeus cubicularis, from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho(Montana State University - Bozeman, College of Letters & Science, 2017) Krumenacker, L. J.; Chairperson, Graduate Committee: David Varricchio; David J. Varricchio, Chris Organ, Clint Boyd and Brooks Britt were co-authors of the article, 'Osteology and phylogeny of the neornithischian dinosaur Oryctodromeus cubicularis from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.; David J. Varricchio, John Wilson and Ashley Ferguson were co-authors of the article, 'Taphonomy of Oryctodromeus cubicularis from the mid-Cretaceous (Albian-Cenomanian) of Idaho, and additional Oryctodromeus burrows from Idaho and Montana' submitted to the journal 'Palaeogeography, palaeoclimatology, palaeoecology' which is contained within this thesis.; David J. Varricchio, John R. Horner and Kelli Taddy were co-authors of the article, 'Ontogenetic histology and growth of the neornithischian dinosaur Oryctodromeus cubicularis from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.Oryctodromeus is a small bipedal dinosaur known from middle Cretaceous (95-100 My) Wayan Formation of Idaho and the Vaughn Member of the Blackleaf Formation of Montana. This taxon is hypothesized to be a burrowing dinosaur, which cared for its young within these burrows. This dissertation is a broad three-part treatment of this taxon, and excepting the introductory and concluding chapters this dissertation consists of three main chapters. Chapter two describes the osteology and phylogenetic relationships of this animal. Notable features of the Oryctodromeus skeleton described include a network of ossified tendons along the vertebral column that completely ensheath the tail, a long tail that forms more than half the length of the animal, and unusual femoral heads whose morphology may be related to burrowing behavior. The first full skeletal and skull reconstructions of this animal are presented. Chapter three investigates patterns of preservation of Oryctodromeus. Data suggests that preservation of single to multiple individuals of this taxon typically occurred in burrows that may be difficult to impossible to recognize in the fossil record. New examples of burrows from Oryctodromeus from the Vaughn and Wayan, as well as additional evidence for social behavior, are also described. A third chapter details the ontogenetic histology, growth rates and patterns of skeletal fusion based on seven limb elements (femora and tibiae) from different individuals. Based on the data in this dissertation, three growth stages can be recognized in Oryctodromeus based on bone histology. Juveniles are defined by more rapidly growing fibrolamellar tissue, sub-adults are defined by a cortex of inner fibrolamellar tissue and outer zonal parallel fibered tissue, and near-adult individuals have tissue similar to sub adults with dense avascular bone in the outermost cortex that signals a decrease in growth rate. LAG's suggest a minimum age of six to seven years for more mature individuals. Patterns of neurocentral fusion in Oryctodromeus appear similar to those of crocodylians and some other small ornithischians, while the growth rates of Oryctodromeus appear slower than those of some dinosaurs, but similar to taxa such as Orodromeus and Tenontosaurus.Item Histovariability and growth in the basal ceratopsian dinosaur Psittacosaurus mongoliensis from the lower Cretaceous Khulsangol Formation, central Mongolia(Montana State University - Bozeman, College of Letters & Science, 2016) Zorigt, Badamkhatan; Chairperson, Graduate Committee: David Varricchio; John R. Horner (co-chair); John R. Horner and Khatanbaatar Purevdorj were co-authors of the article, 'Taphonomy and depositional environment of a monodominant Psittacosaurus bonebed from the lower Cretaceous Khulsangol Formation of central Mongolia' submitted to the journal 'Journal of vertebrate paleontology ' which is contained within this dissertation.; John R. Horner was a co-author of the article, 'Intraskeletal histovariability in the hind limb of Psittacosaurus mongoliensis' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this dissertation.; John R. Horner was a co-author of the article, 'Ontogenetic histovariability in a population of Psittacosaurus mongoliensis from the lower Cretaceous Khulsangol Formation, Uvurkhangai Province, Mongolia' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this dissertation.Large datasets are required in order to study the details of growth in non-avian dinosaurs. The Cretaceous dinosaur sites in Mongolia offer tremendous opportunities to collect a sufficient data for such study. This dissertation introduces a brief history of dinosaur research in Mongolia. As a result of many expeditions since the 1920s, numerous new dinosaurs were named and many new dinosaur localities have been discovered. Whereas the majority of studies of Mongolian dinosaurs have focused on the fossils of Late Cretaceous taxa, dinosaur fossils are also abundant in the Early Cretaceous dinosaur sites. One of the richest Early Cretaceous dinosaur sites is Builst Khudag (BLK) in central Mongolia. Sedimentologic and taphonomic studies of the BLK site suggest that the depositional environment of the locality indicates the occurrence of a debris flow and sheet-flood in an alluvial setting. The fossils of the parrot-beaked, herbivorous dinosaur Psittacosaurus is the most common taxon from the BLK site. A Psittacosaurus aggregation consisting of juveniles reflects a catastrophic mortality event. Previously, the humerus, femur, tibia, and fibula were suggested to represent the ideal bones for growth determination studies. Since various elements grow in different developmental regimes, it is necessary to further determine an ideal element for Psittacosaurus growth assessment. Associated femora, tibiae, and fibulae from four individuals were examined. The femur and tibia show comparable bone tissues in all individuals; the tibia and fibula present comparable numbers of growth lines. Based on this finding, the tibia appears to provide the most comprehensive view of growth in Psittacosaurus. The Psittacosaurus growth strategy was further assessed using 58 tibiae collected from the BLK site. The Psittacosaurus growth rate reaches its peak (3.19 microns/day) after passing the threshold size at the age of two. During the ages of 10-13, the body size reaches 170.3 cm in length and the growth rate is considerably slowed down. This study confirms that Psittacosaurus growth fits in a sigmoidal shaped curve.Item Paleoenvironment and taphonomy of the fauna of the Tullock Formation (early Paleocene), McGuire Creek area, McCone County, Montana(Montana State University - Bozeman, College of Letters & Science, 1992) Katsura, YoshihiroItem Sedimentology and taphonomy of a shell bed assemblage from the Upper Cretaceous (Maastrichtian) Hell Creek Formation of eastern Montana(Montana State University - Bozeman, College of Letters & Science, 2001) Shoup, Bentley EdwardItem Fluvial systems of the Upper Jurassic Morrison Formation, northern Beartooth and Gallatin Ranges, southwest Montana(Montana State University - Bozeman, College of Letters & Science, 1993) Cooley, Jonathan Todd; Chairperson, Graduate Committee: James G. Schmitt; John R. Horner (co-chair)