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 Fossil eggs and perinatal remains from the upper Cretaceous Two Medicine Formation of Montana : description and implications(Montana State University - Bozeman, College of Letters & Science, 2014) Oser, Sara Elizabeth; Co-chairpersons, Graduate Committee: Frankie Jackson and David Varricchio; Frankie D. Jackson was a co-author of the article, 'Sediment and eggshell interactions: using abrasion to assess transport in fossil eggshell accumulations' in the journal 'Historical biology' which is contained within this thesis.Egg Mountain is a dinosaur nesting site located in the Upper Cretaceous, Two Medicine Formation of western Montana. The site was located on a coastal plain with seasonal variations in rainfall and was utilized as a nesting location by several taxa. Egg Mountain hosts a remarkable diversity of fossil eggshell and is a window into the reproductive behavior of multiple extinct taxa. A recent 4x6 m excavation revealed two clusters of unidentified eggs, 185 Spheroolithus eggshell fragments, and perinatal osteological remains within homogenous siliciclastic mudstone. Insect burrows (Celliforma) and cocoons (Rebuffoichnus) were excavated from the micritic limestone bed capping the excavation. The objectives of this thesis are to 1) describe the eggs and eggshell fragments, 2) determine nesting environment, 3) assign the osteological remains to taxon, and 4) investigate the taphonomic history of the site. Analytical methods include scanning electron microscopy, cathodoluminescence, petrographic microscopy, and ImageJ photo analysis. The lithologically compressed, unidentified 12 cm diameter eggs occur in two clusters containing 7-22 eggs. Diagenetic alteration obscures eggshell microstructure, inhibiting ootaxonomic assignment of the 0.5 mm thick eggshell. The 0.8-1.3 mm thick fragmentary eggshell is assigned to Spheroolithus albertensis based on microstructure, sagenotuberculate ornamentation, and prolatocanaliculate/ rimocanaliculate pores. To assess taphonomic history of the Spheroolithus fragments, chicken (Gallus gallus domesticus) and ostrich (Struthio camelus) eggshells were placed in a tumbler with water and quartz sand to simulate transport. The resulting wear on these fragments was compared to unabraded eggshell. In addition, modern eggshell was compared to fossil eggshells from a fossil nesting site, crevasse splay and channel deposits, and Egg Mountain. Spheroolithus eggshell from Egg Mountain lack edge rounding and resemble fossil eggshell from a nesting site and unabraded modern eggshell, suggesting a parautochthonous assemblage. Spheroolithus and unidentified eggs from cluster 1 respectively have gas conductance values 16-32x and 4-13x higher than avian eggs of the same mass, suggesting enclosed nest environments. The morphology of the humerus and skull elements of the perinatal osteological remains is consistent with the Hadrosauridae, though the juvenile status and incomplete nature of the specimen inhibits further taxonomic assignment.Item Giant dinosaur (theropod) eggs of the Oogenus macroelongatoolithus (Elongatoolithidae) from southeastern Idaho : taxonomic, paleobiogeographic, and reproductive implications(Montana State University - Bozeman, College of Letters & Science, 2014) Simon, Danielle Jade; Chairperson, Graduate Committee: David VarricchioMacroelongatoolithus eggs are best known for their gigantic size and elongate shape, ranging from 34 - 61 cm in length with an elongation index of 2-3.1. Ootaxonomic placement of this oogenus, and the oospecies within it, has varied widely among authors, necessitating a re-evaluation of the group. This study represents the first comprehensive comparison of gross morphology, microstructural variation, and gas conductance within a Macroelongatoolithus oospecies. Four specimens, egg pair IMNH 2428\49608 and additional eggshell from the Albian-Cenomanian Wayan Formation of Idaho, eggshell fragment ES305 from the Albian-Cenomanian Blackleaf Formation of Montana, eggshell fragment thinsections ES301 and ES305-306 from the early Late Cretaceous Thomas Fork Formation of Wyoming, and egg pair ZMNH M8705 from the Cenomanian-Turonian Liangtoutang Formation of China, are examined, described, and assigned to the oospecies Macroelongatoolithus carlylei. Eggs are 39.8 - 41.65 cm long and 10.8 - 14.28 cm wide, with an eggshell thickness ranges from 1.01 - 2.17 mm, and CL:ML ratio ranging from 2.05:1 - 7.68:1. Eggshell consists of two structural layers of calcite separated by a distinct, undulating boundary. Gas conductance of IMNH 2428\49608-2 and ZMNH M8705-1 is 1119 - 1597 mg H2O torr-1 day-1, 2.9 - 5.6 times higher than values predicted for open nest mass-equivalent eggs. These values suggest a humid or enclosed nesting environment. The lower value calculated for the Liangtoutang Formation specimen (ZMNH M8705-1) may reflect differences in nesting environment between the semi-arid floodplain mudstones of the Wayan Formation in Idaho and the shallow laucustrine red siltstones and sandstones of the Liangtoutang Formation of Zhejiang, China. The observed microstructural variation within and between IMNH 2428/49608 and ZMNH M86705 expands the range of expected variation for an oospecies, and calls into question the over splitting of ootaxa on the basis of traits that may reflect individual variation or growth stage of the laying animal. The discovery and description of an intact M. carlylei specimen from North American confirms the synonymy of M. xixiaensis into the previously named M. carlylei suggested by Zelenitsky et al. 2000, and expands the geographic and temporal distribution of the oogenus and parent animal to include the Albian - Cenomanian of North America.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.Item Sedimentological analyses of eggshell transport and deposition : implication and application to eggshell taphonomy(Montana State University - Bozeman, College of Letters & Science, 2013) Imai, Takuya; Chairperson, Graduate Committee: David VarricchioThe interpretation of fossil eggshell assemblages in the absence of nesting structures is problematic because eggshells can be transported by hydraulic flows in fluvial environments. Failure to recognize transported eggshells may lead to erroneous interpretation of the reproductive behavior and ecology of those animals. An inconsistent array of evidence has been used in past studies to assess eggshell transport. Here, a series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. Using modern eggshells in a flume, I investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell shape and size, and size of clastic sediment expected to be associated with transported eggshells. Emu, goose, and ostrich eggshell fragments were released in a rectangular flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinylchloride). At eggshell deposition, eggshell orientation and flow depth were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition. The probability of concave-down orientation for deposited eggshells was estimated for each eggshell type transported on each substrate. The relationship of the critical bed shear stress for eggshell deposition with eggshell shape and size was tested. Size of clastic grains deposited under the critical bed shear stress for eggshell deposition was estimated. The probability of concave-down orientation after transport was > 85% regardless of eggshell types and substrates. The bed shear stress at eggshell deposition was most closely related to eggshell height and volume. Estimated size of clastic sediment associated with transported eggshell was coarse sand or coarser sediment. One may consider a high proportion of concave-down oriented eggshells in fossil assemblages as indicative of transport regardless of eggshell types. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in matrix of fossil eggshells may be used as evidence of eggshell transport. Further studies are necessary to test reliability of those techniques and broaden their applicability.Item Carbonate preservation of dinosaur eggs in the upper Cretaceous Anacleto Formation at Auca Mahuevo, Neuquen Basin, Argentina(Montana State University - Bozeman, College of Letters & Science, 2011) Anggraini, Niswatin Wahida; Chairperson, Graduate Committee: James G. SchmittPreservation of dinosaur eggs and footprints by precipitation of calcium carbonate in the Upper Cretaceous Anacleto Formation at Auca Mahuevo, Argentina represents a relatively unusual occcurence in the fossil record. Under normal condition, eggs are readily destroyed in sediments shortly after burial by physical, chemical, and biological processes. This study attempts to determine a preservational model for carbonate eggs by characterizing their mineralogical composition and microstructures using a variety of analytical instruments including petrographic microscope, cathodoluminesce (CL) microscope, X-ray powder diffraction (XRD) and field-emission scanning electron microscope (FEM) to characterize the composition and fabric of the fossilized eggs. Several textutal features have been observed in the carbonate eggs, including membrane, embryonic skin, spherulites, ooids, peloids, Microcodium, calcified filaments, and micrite. Microbial actvity is likely responsible for the formation of these microfabric features, facilitating calcium carbonate precipitation leading to exceptional preservation of eggs. Although microbial influence in the carbonate egg preservation has not been clearly elucidated, laboratory experiments by other workers provide an argument for the role of microbes in the precipitation of calcium carbonate. The rare preservation of egg contents in the Anacleto Formation have been linked to biological-mediated processes. This preservation also provides evidence for penecontemporaneous carbonate precipitation under subaerial conditions before significant burial.Item Titanosaur reproductive biology : comparison of the Auca Mahuevo Titanosaur nesting locality (Argentina), to the Pinyes Megaloolithus nesting locality (Spain)(Montana State University - Bozeman, College of Letters & Science, 2007) Jackson, Frances Drew; Chairperson, Graduate Committee: David VarricchioTaphonomic and microstructural studies at the Late Cretaceous Auca Mahuevo titanosaur nesting site (Argentina) reveal significant differences in reproductive attributes compared to alleged sauropods producing Megaloolithus eggs at the Pinyes locality (Spain). Auca Mahuevo clutches contain 15-40 M. patagonicus eggs; many of the 12-14 cm eggs contain titanosaur remains. Six clutches include both normal and abnormal eggs exhibiting three types of abnormal morphology: Type I displays two normal, superimposed eggshells, while Type II and III exhibit a normal inner eggshell, with one and three overlying eggshells, respectively. Previous studies that endeavor to link egg abnormalities to dinosaur extinction lack taphonomic and rigorous statistical methods. The Pinyes locality occurs in the Tremp Formation, exposed in the Spanish Pyrenees. The overbank deposits contain clutches with 4-12 eggs; none of the 16-24 cm M. Siruguei eggs contain embryos. Although often assigned to sauropod dinosaurs, M. siruguei differs from M. patagonicus in clutch size, egg volume, shell thickness, pore density, and incubation mode; thus, taxonomic assignment to sauropods seems questionable.