Theses and Dissertations at Montana State University (MSU)
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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 Modeling the evolution of substrate use in the hands and feet of primates, birds, and non-avian theropod dinosaurs(Montana State University - Bozeman, College of Letters & Science, 2012) Stiegler, Josef Barrett; Chairperson, Graduate Committee: David VarricchioThe hands and feet of non-avian theropods have historically been characterized as structures adapted for grasping prey items and for cursorial locomotion, respectively. The purpose of this study was to challenge those assumptions in light of observations on the intradigital proportions of the hands and feet of theropods compared to modern taxa. Linear measurements of elements from the hands of mammals and squamates, the feet of birds, and both the hands and feet of non-avian theropods were collected to observe clustering of taxa in morphospace. The evolution of each linear character was modeled for primates, birds, and non-avian theropods using Ornstein-Uhlenbeck models in the "OUCH!" software package. Brownian motion models were nearly universally rejected in favor of single and multi-optimum selection based models. Model testing indicated directional selection for the most proximal and distal non-ungual elements in each digital ray, and either stabilizing selection or brownian motion processes for intermediate elements. The results for models applied to non-avian theropods suggest selection for metacarpal proportions convergent with arboreal mammals, and proportions of the penultimate phalanx similar to the feet of birds that use clawed adhesion for vertical substrate use and predation. We propose that "clinging" as opposed to "grasping" is a more apt hypothesis for behavior leading to elongation of the penultimate phalanx, as is the case in most non-avian theropods. According to modeling results, microraptorine dromaeosaurids evolved proportionally long metacarpals relative to their manual phalanges convergently with birds, and were comparable to other non-avian theropods in pedal proportions. These results contradict previous hypotheses in the literature regarding arboreal substrate use within microraptorinae. The scansoriopterygid Epidendrosaurus was a slight outlier in both manual and pedal proportions from other non avian maniraptorans, but adaptation for an arboreal lifestyle in this taxon is not supported by this analysis. The "Raptor Prey Restraint" model for predatory behavior in deinonychosaurian theropods was rejected by this analysis, though it is likely that the evaluated traits fail to capture the necessary anatomical variation to more fully test this hypothesis.