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Item A transitional species of Daspletosaurus Russell, 1970 from the Judith River Formation of eastern Montana(PeerJ, 2022-11) Warshaw, Elías A.; Fowler, Denver W.Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. D. wilsoni displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to D. torosus and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in D. horneri and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within Daspletosaurus and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anagenetic evolution among contemporary dinosaur lineages.Item Hydrothermal influences on the Holocene environmental history of central Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2020) Schiller, Christopher Michael; Chairperson, Graduate Committee: Cathy Whitlock; Cathy Whitlock, Kathryn L. Elder, Nels A. Iverson and Mark B. Abbott were co-authors of the article, 'Erroneously old radiocarbon ages from terrestrial pollen concentrates in Yellowstone Lake, Wyoming, USA' in the journal 'Radiocarbon' which is contained within this dissertation.; Rosine Cartier, Cathy Whitlock and Lisa A. Morgan were co-authors of the article, 'Multi-proxy record of Holocene paleoenvironmental conditions from Yellowstone Lake, Wyoming, USA' submitted to the journal 'Quaternary science reviews' which is contained within this dissertation.; Cathy Whitlock, Sabrina R. Brown and Petra Zahajska were co-authors of the article, 'Holocene geo-ecological evolution in Lower Geyser Basin, Yellowstone National Park' submitted to the journal 'Geological Society of America bulletin' which is contained within this dissertation.; Cathy Whitlock, Mio Alt and Lisa A. Morgan were co-authors of the article, 'Vegetation responses to Quaternary volcanic and hydrothermal disturbances in the northern Rocky Mountains and Greater Yellowstone Ecosystem' in the journal 'Palaeogeography, Palaeoclimatology, Plaeoecology' which is contained within this dissertation.The postglacial vegetation history of Yellowstone National Park is well established by past paleoecological studies, but the role of hydrothermal activity--pervasive in areas of the park--in that history is poorly understood. To address this unknown, pollen and charcoal records were examined from lake sediment cores at multiple sites in central Yellowstone National Park to reconstruct Holocene vegetation. First, radiocarbon ages obtained from pollen concentrates were compared with other age controls at Yellowstone Lake, revealing ages that were up to 4300 cal years too old. Erroneous ages were due to either old carbon contamination from magmatic or hydrothermally degassed CO 2 or old pollen reworked from an unknown source. Second, Holocene vegetation and fire history were reconstructed from a Yellowstone Lake sediment core. The record was characterized by gradually increasing closure or extent of Pinus contorta forest and increasing fire activity to the present, consistent with reduced summer insolation creating cooler, effectively wetter conditions in central Yellowstone National Park. No impact of hydrothermal activity was detected in the regional Holocene-long vegetation and fire histories. Third, Holocene vegetation and fire history were studied at Goose Lake in Lower Geyser Basin, an area with abundant modern hydrothermal activity. The vegetation and fire history diverged from the regional trend at 3800 cal yr BP, synchronous with geochemical indicators indicating reorganization of hydrothermal activity in the basin, suggesting an abrupt ecological response to shifting hydrothermal activity. Finally, a variety of volcanic and hydrothermal processes were investigated as disturbances in the Northern Rocky Mountains and Yellowstone National Park through high-resolution pollen analysis. Hydrothermal explosion deposits were found to be synchronous with conifer morality, in some records, indicating that the effects of hydrothermal explosions are local and short-lived. At a regional scale, it is evident that vegetation changes were chiefly responding to millennial-scale, insolation-driven climate change. However, the impacts of hydrothermal activity were locally important where pervasive, as in Lower Geyser Basin, and in areas recently affected by hydrothermal explosions.Item Late Holocene vegetation and fire history in subalpine forests of northwestern Montana(Montana State University - Bozeman, College of Letters & Science, 2020) Sly, Shelby Fulton; Chairperson, Graduate Committee: David McWethyMid-to high- elevation forests of the Northern Rocky Mountains are dynamic systems that change in time in response to climate, disturbance and human activities. Climate models suggest these ecosystems will experience warmer temperatures, decreased spring snowpack, drier summers, and longer fire seasons, highlighting a need to better understand how these systems respond to changing climatic conditions. Sediment cores were extracted from two lakes in the Mission and Reservation Divide Mountains of Montana and analyzed for pollen and macroscopic charcoal to reconstruct fire and vegetation histories. The records from Mud Lake and Three Lakes Peak span the last 5400 and 4600 years respectively, and highlight the long-term persistence and relative stability of closed, mixed conifer/subalpine forests. During the mid-Holocene (approx. ca. 5000 yr BP), Pinus pollen percentages increased, suggesting closed forests which then transitioned to mesic forest of Pinus, Abies, and Picea over the last ca. 4000 years. Modern forests established between 3500-3000 cal yr BP at both sites. Both sites experience elevated fire activity during the Medieval Climate Anomaly c. 1000-900 cal yr BP which is consistent with other sites in the region. While relatively infrequent (2-4 fires per millennia), wildfires played a role in maintaining early successional vegetation (Poaeceae, Alnus spp.) and taxa that benefit from post-fire reduction in competition such as five-needle pines. Paleoenvironmental records from these two sites indicate subalpine forests of northwestern Montana persisted with relative stability throughout the mid to late-Holocene. With projections for increased warming, longer fire seasons and the possibility for increased occurance of short-interval fires in higher elevation ecosystems of the Northern Rocky Mountains, subalpine forests may become vulnerable to rapid transitions to different forest types or even non-forest systems.Item Late Holocene climate, fire, and vegetation history on the northern range, Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2019) Firmage, David Samuel; Chairperson, Graduate Committee: Cathy WhitlockYellowstone National Park is an iconic natural landscape that encompasses unique geologic features as well as a diverse and ecologically important flora and fauna. The ecological resilience of the Northern Range of the park, home to the park's ungulate herds, faces an uncertain future with a projected warming climate over the next century. Understanding the variability of vegetation organization in response to past changes in climate can help park managers plan for future climate scenarios. Lake sediment cores from two lakes were collected, analyzed for pollen type, charcoal accumulation and lithological components, and compared with other studies to highlight commonalities in fire-histories and vegetation trends across the Northern Range over the past 4000 cal yr BP. Foster Lake the records suggest fire-episodes and changes to lake productivity and between ~3500-2900 cal yr BP, large intense fire-episodes between ~2500-2150 cal yr BP, ~1000 cal yr BP and frequent large fire episodes from ~700 cal yr BP to the present day. Floating Island Lake records between ~4000-3000 cal yr BP suggest the site experienced infrequent, large fire episodes concurrent with periods of protracted drought and decreases in water level. Between ~3000-1500 low intensity fire episodes were common, punctuated by infrequent large fire episodes at ~2900, ~2250, ~2050 and ~1880 cal yr BP. During the last ~1ka two fire episodes were recorded at Floating Island Lake, at ~1030 cal yr BP coincident with the Medieval Climate Anomaly, and 270~ cal yr BP during the Little Ice Age. A comparison of fire histories from studies spanning the Northern Range shows that during periods of protracted drought large fire episodes are common across the landscape, and that during periods of moderate climate fire size and severity is likely modulated by local site controls such as topography and vegetation structure. This study shows that fire episodes in the Northern Range have occurred as a spatial and temporal mosaic, and are likely to continue to do so. Additionally, this study increases our understanding of how vegetation structure and fire regimes in the Northern Range have varied as a result of a range of climate conditions in the past. Such baseline information helps us anticipate some of the ecological responses that may occur in the decades ahead with global warming.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 Description and ontogenetic assessment of a new Jehol microraptorine(Montana State University - Bozeman, College of Letters & Science, 2014) Poust, Ashley William; Chairperson, Graduate Committee: David VarricchioFossils from the Jehol Group (Early Cretaceous, Liaoning Province, China) have greatly contributed to our understanding of the morphology and diversity of Paraves, the group of dinosaurs including sickle-clawed dromaeosaurs, large-brained troodontids, and avialians, the ancestors of modern birds. However, many taxa are represented by only a few specimens of unclear ontogenetic age. Without a thorough understanding of ontogeny, the evolutionary relationships and significance of character states may be obscured within paravian dinosaurs. A complete specimen of a new taxon of microraptorine dromaeosaur, Wulong bohaiensis gen. et sp. nov., from the Jiufotang Formation (upper Jehol Group) exhibits clearly juvenile morphology. The dinosaur is small and preserved in articulation on a single slab. It has microraptorine features such as a subarctometatarsalian foot, a short first manual digit, and a prominent tubercle on the pubis. Phylogenetic analysis substantiates this assignment. It also possesses more than 29 tail vertebrae, inclined pneumatic foramina on its dorsal vertebrae, and an unusually large coracoid fenestra, which with other features argue that it is a new taxon. This individual shows many osteological markers of immaturity identified in other archosaurs. Skull elements, all visible neurocentral sutures, pubes, and proximal tarsals remain unfused. Grainy surface texture of the cortical bone and poor ossification of long bone articular surfaces further supports an immature status. Histologic samples of the tibia, fibula, and humerus of this individual (the first microraptorine theropod to be sampled) confirm that it was around a single year in age and still growing at death, but that the growth had slowed. This slow down in growth is interesting in light of the presence of pennaceous feathers extending from the fore- and hind-limbs and, notably, two long plumes extending more than 12 cm from the tip of the caudal series. This indicates that presence of a variety of feather types, including filamentous feathers, pennaceous primaries, and long rectrices, likely used for ornamentation, preceded skeletal maturity and full adult size.Item Vertebrate microfossils from the Upper Freshwater Molasse in the Swiss Molasse Basin: Implications for the evolution of the North Alpine Foreland Basin during the Miocene Climate Optimum(2015-05) Jost, Jürg; Kälin, Daniel; Börner, Saskia; Vasilyan, Davit; Lawver, Daniel R.; Reichenbacher, BettinaThe older part of the Upper Freshwater Molasse (OSM) in the Swiss and South German Molasse Basin records the extended warm period known as the Miocene Climate Optimum. However, dating and global correlation of fossils and palaeoclimatic data from OSM sediments remains challenging, because sections are often incomplete and biostratigraphic data sometimes ambiguous. Here we present the rare case of a fossiliferous OSM section that can be securely dated to the late Early Miocene and early Middle Miocene (c. 16.1–15.7 Ma). Vertebrate microfossils have been recovered from three levels in superposition. Fish teeth document primary freshwater fishes (Cyprinidae, Channidae), but otoliths found in the middle level indicate dominance of euryhaline fishes (Cyprinodontiformes, Gobiiformes). The herpetofaunal assemblages largely consist of taxa that were widely distributed in Central Europe during the Miocene Climate Optimum and fragments of turtle eggshells assignable to the Oofamily Testudoolithidae Hirsch, 1996. The small-mammal fauna is dominated by the cricetid Megacricetodon bavaricus Fahlbusch, 1964. The fossil biota implies that the lowermost level (late Early Miocene, c. 16.1 Ma) represents a palaeo-soil that formed under humid conditions, while the levels above it (early Middle Miocene, c. 15.7–15.8 Ma) record a warm freshwater pond subject to evaporation (middle level), and mean annual temperature ≥ 17 °C in the vicinity of a river with an open hinterland (upper level). Our results, together with previous data, suggest that the palaeoclimate of the North Alpine Foreland Basin of Switzerland and Southwest Germany was humid during the late Early Miocene and earliest Middle Miocene, and that the Middle Miocene onset of seasonality and low mean annual precipitation occurred by c. 15.7–15.8 Ma. We conclude that global climate change and the 100-kyr orbital eccentricity minimum at 15.75 Ma may have triggered the decrease in humidity in the North Alpine Foreland Basin.Item From dinosaurs to birds: a tail of evolution(2014-05) Rashid, Dana J.; Chapman, Susan C.; Larsson, Hans C. E.; Organ, Chris L.; Merzdorf, Christa; Bradley, Roger S.; Horner, John R.A particularly critical event in avian evolution was the transition from long- to short-tailed birds. Primitive bird tails underwent significant alteration, most notably reduction of the number of caudal vertebrae and fusion of the distal caudal vertebrae into an ossified pygostyle. These changes, among others, occurred over a very short evolutionary interval, which brings into focus the underlying mechanisms behind those changes. Despite the wealth of studies delving into avian evolution, virtually nothing is understood about the genetic and developmental events responsible for the emergence of short, fused tails. In this review, we summarize the current understanding of the signaling pathways and morphological events that contribute to tail extension and termination and examine how mutations affecting the genes that control these pathways might influence the evolution of the avian tail. To generate a list of candidate genes that may have been modulated in the transition to short-tailed birds, we analyzed a comprehensive set of mouse mutants. Interestingly, a prevalent pleiotropic effect of mutations that cause fused caudal vertebral bodies (as in the pygostyles of birds) is tail truncation. We identified 23 mutations in this class, and these were primarily restricted to genes involved in axial extension. At least half of the mutations that cause short, fused tails lie in the Notch/Wnt pathway of somite boundary formation or differentiation, leading to changes in somite number or size. Several of the mutations also cause additional bone fusions in the trunk skeleton, reminiscent of those observed in primitive and modern birds. All of our findings were correlated to the fossil record. An open question is whether the relatively sudden appearance of short-tailed birds in the fossil record could be accounted for, at least in part, by the pleiotropic effects generated by a relatively small number of mutational events.Item An integrative approach to understanding bird origins(2014-12) Xu, Xing; Zhou, Zhonghe; Dudley, Robert; Mackem, Susan; Chuong, Cheng-Ming; Erickson, Gregory M.; Varricchio, David J.Recent discoveries of spectacular dinosaur fossils overwhelmingly support the hypothesis that birds are descended from maniraptoran theropod dinosaurs, and furthermore, demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system originated among Mesozoic terrestrial dinosaurs. The transition from ground-living to flight-capable theropod dinosaurs now probably represents one of the best-documented major evolutionary transitions in life history. Recent studies in developmental biology and other disciplines provide additional insights into how bird characteristics originated and evolved. The iconic features of extant birds for the most part evolved in a gradual and stepwise fashion throughout archosaur evolution. However, new data also highlight occasional bursts of morphological novelty at certain stages particularly close to the origin of birds and an unavoidable complex, mosaic evolutionary distribution of major bird characteristics on the theropod tree. Research into bird origins provides a premier example of how paleontological and neontological data can interact to reveal the complexity of major innovations, to answer key evolutionary questions, and to lead to new research directions. A better understanding of bird origins requires multifaceted and integrative approaches, yet fossils necessarily provide the final test of any evolutionary model.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, Yoshihiro