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 The evolution of facial keratin and tooth distribution: implications for the coevolution of traits in dinosaurs(Montana State University - Bozeman, College of Letters & Science, 2021) Aguilar-Pedrayes, Isaura; Chairperson, Graduate Committee: David VarricchioResearch on birds indicates that the occurrence of beak keratin and teeth are mutually exclusive, and both traits are widely distributed across Dinosauria. The macroevolution of the antagonistic relationship between keratinous beaks and teeth has only recently been explored, and these studies focus on Aves and non-avian Coelurosauria. Currently, many hypotheses posit an adaptive advantage for the trade-off of these two traits but have not been tested on a macroevolutionary scale. Examples in non-coelurosaurian dinosaurs and non-adaptive alternatives, such as trait evolution correlation and phylogenetic history, have yet to be explored thoroughly-. This study assesses the current evolutionary assumptions of beak-like keratin and tooth distribution across dinosaurs using recently-developed variable rate phylogenetic comparative methods. The diagnostic bone surface used as a proxy for the keratin cover in fossil jaws is smooth grooved textures with foramina at the jaw tips. The effect of a keratin cover on the tooth distribution within individuals is tested with Markov Chain Monte Carlo (MCMC) multinomial regression models. Coevolutionary rates for these structures are evaluated with Bayesian RJ-MCMC algorithms. The best-fit model is determined using Bayes Factors. The taxonomic breadth increased the evolutionary sample size and thus analytical power but forced a simplified coding scheme for beak and tooth traits. My analysis shows that the presence of a keratin cover influences the evolution of partial toothrow reduction but not complete tooth loss. Another factor could have driven the evolution of toothless beaks in some dinosaurs. In addition, the evolution of a reduced toothrow only precedes the presence of a keratin cover in the Theropoda lineage. Furthermore, the evolutionary rate of toothrow distribution was higher and more diverse when a keratin cover was absent; this suggests that the keratin cover imposes a functional constraint on tooth diversity at macroevolutionary scales.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 Dinosaurs and time: chronostratigraphic frameworks and their utility in analysis of dinosaur paleobiology(Montana State University - Bozeman, College of Letters & Science, 2016) Fowler, Denver Warwick; Chairperson, Graduate Committee: John R. Horner; John B. Scannella and John R. Horner were co-authors of the article, 'Transitional evolutionary forms and stratigraphic trends in Chasmosaurine ceratopsid dinosaurs' which is contained within this dissertation.; Holly N. Woodward, Elizabeth A. Freedman, Peter L. Larson and John R. Horner were co-authors of the article, 'Reanalysis of 'Raptorex kriegsteini': a juvenile tyrannosaurid dinosaur from Mongolia' in the journal 'PLOS ONE' which is contained within this dissertation.; This dissertation contains two articles of which Denver W. Fowler is not the main author.Stratigraphy is the study of the position of rock strata, in order to determine their age. Dinosaur fossils have been recovered from North America for over 150 years, yet the stratigraphy of the localities from which they were collected has rarely been analysed at high resolution, either due to lack of original locality data, or that precise correlation between depositional basins was not technologically possible. This dissertation analyses what effect the introduction of high-resolution chronostratigraphic data has on our understanding of dinosaur paleobiology. Terrestrial sequence stratigraphy was used in combination with previously published data in order to subdivide the uppermost Cretaceous Hell Creek Formation of Montana into lower, middle, and upper units, shown to be consistent across the formation type area. Similar stratigraphic data was gathered for each of the Late Cretaceous dinosaur-bearing formations of the North American Western Interior, which was combined with nearly 200 radiometric dates (newly recalibrated here) to plot a comprehensive high-resolution correlation chart. The stratigraphic occurrence of dinosaur taxa was consequently plotted upon this chart. Similarly, the new Hell Creek Formation stratigraphic framework was used to plot the stratigraphic occurrence of Triceratops fossils. From this it can be seen that many dinosaur groups form stacks of stratigraphically separated species, a pattern indicative of linear, non-branching evolution (anagenesis). A similar pattern is observed for two new taxa of chasmosaurine ceratopsid (horned) dinosaurs from New Mexico, which form morphologic and stratigraphic intermediates between the slightly older taxon, Pentaceratops, and the younger Anchiceratops. Phylogenetic and geometric morphometric analysis supports the hypothesis that the posterior embayment of the parietal deepens and closes in on itself over ~ 2 million years from Pentaceratops through the new taxa, to Anchiceratops, and suggests a deep split within Chasmosaurinae that occurs before the Middle Campanian. These findings imply that dinosaur evolution in the Late Cretaceous Western Interior was characterized mostly by anagenesis, punctuated by occasional speciation events, perhaps triggered by high sealevel creating a north / south geographic barrier. The evolutionary process of reinforcement is discussed as a possible mechanism for the development of cranial display organs, linked to speciation.Item Osteology and variation of Brachylophosaurus canadensis (Dinousauria, Hadrosauridae) from the Upper Cretaceous Judith River formation of Montana(Montana State University - Bozeman, College of Letters & Science, 2001) Prieto-Marquez, AlbertItem Sedimentology and taphonomy of a dinosaur bonebed from the Upper Cretaceous (Campanian) Judith River Formation of north central Montana(Montana State University - Bozeman, College of Letters & Science, 2000) LaRock, Jeffrey WilliamItem Epaxial muscles and ossified tendons in dinosaurs : anatomy, development, histology, and biomechanics(Montana State University - Bozeman, College of Letters & Science, 2003) Organ, Christopher Lee; Chairperson, Graduate Committee: John R. HornerItem Jack's birthday site, a diverse dinosaur bonebed from the Cretaceous Two Medicine Formation of Montana(Montana State University - Bozeman, College of Letters & Science, 1995) Varricchio, David Joseph; Chairperson, Graduate Committee: John R. Horner; Robert E. Moore (co-chair)Jack's Birthday Site, a diverse vertebrate assemblage from the Upper Cretaceous Two Medidne Formation of western Montana, was taphonomically investigated and compared with other predominantly iguanodontoid bonebeds from the area. The large bone sample at Jack's Birthday Site allowed statistical evaluation of the preservational and compositional variation within the site. Evidence, including sedimentary fades, plant and invertebrate fossils, and bone orientation and condition, indicates Jack's Birthday Site represents part of a small, shallow floodplain lake. Lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m, representing a transition from lake through shoreline to marginal shoreline/floodplain environments. The vertebrate assemblage contains ten dinosaur taxa and a variety of non-dinosaurs and indudes two taphonomic fractions. The first, consisting of attritional, predominantly isolated and allochthonous elements, represents a time-averaged assemblage. The other consists of assodated, parautochthonous remains restricted to a single horizon. Taxa represented by associated remains indude three iguanodontoids, Hypacrosaurus, Prosaurolophus, and Gryposaurus, and the theropod Troodon. Associated individuals of these taxa have non-random distributions within the site and observed taxonomic dustering may reflect group behavior and/or event mortality. The four or more Troodon represent the first described multiindividual troodontid occurrence. Other predominantly iguanodontoid assemblages, like Jack's Birthday Site, are single highly concentrated bone horizons occurring in silty mudstones. Most are primarily parautochthonous with some degree of skeletal assodation and likely represent mass-mortality. The size-frequency profile of the Camposaur bonebed supports a catastrophic origin. Jack's Birthday Site differs in its diversity, the other localities being nearly monospecific, and its size-frequency profile for iguanodontoids which suggests strongly selective mortality and/or preservation. These plus the site's variable preservation indicate that Jack's Birthday Site is a much more time-averaged assemblage. Both hadrosaurids and lambeosaurids appear to have been gregarious. Lack of association between small (total length <3 m) and larger individuals suggests that juvenile growth rates may have been as rapid as large ungulates. Size-frequency profiles for Maiasaura peeblesorum suggest seasonally synchronous reproduction and high juvenile mortality.Item A phylogenetic approach to understanding dinosaur egg diversity and the evolution of reproductive traits within Dinosauria(Montana State University - Bozeman, College of Letters & Science, 2014) Barta, Daniel Eric; Chairperson, Graduate Committee: David VarricchioFossil eggs provide a unique source of information about the reproductive biology of extinct vertebrates. Dinosaur eggshell, eggs, and clutches are of particular interest because of their great diversity in size, shape, microstructure, and clutch configurations relative to extant egg-laying taxa. In order to provide an explicity phylogenetic framework within which to investigate this diversity and to form more rigorous hypotheses about the identities of egg types that lack associations with adult or embryonic remains, cladistic analyses of 36 oological characters were peformed for 48 egg types. This study aimed to achieve a broader ootaxonomic coverage than previous studies, including pterosaur eggs for the first time in an outgroup with crocodilians and turtles in order to better polarize character states. The first set of analyses did not restrict the positions of ingroup eggs; however, the second utilized a backbone constraint to restrict the positions of taxonomically identified eggs on the tree, allowing unidentified ootaxa to fall out freely relative to a stable framework of relationships based on consensus osteological phylogenies. The results of all analyses reveal Chinese spheroolithids and Mongolian dendroolithids grouping together to the exclusion of other members of those oofamilies (and alongside therizinosauroid eggs) suggesting that Spheroolithidae and Dendroolithidae are polyphyletic. The constrained analysis additionally reveals Ovaloolithus and Cairanoolithus as the only egg types unresolved at the base of Dinosauria on an Adams consensus tree, suggesting that they could belong to either saurischians or ornithischians. All other taxonomically unidentified ootaxa fall out as saurischians, suggesting that the lack of ornithischian eggs in the fossil record is the result of real biases acting against their preservation, and is not simply an artifact of a lack of preserved embryos whereby they might be identified. Major transitions in dinosaur eggshell evolution include the evolution of a second structural layer of calcite within Avetheropoda, and a reversal to a single-layered condition within Therizinosauroidea. As in previous studies, a stepwise accumulation of avian-like character states within theropods precedes the appearance of extant avian clades. This study highlights the need for ongoing application of cladistic and related principles to the study of fossil eggs.