Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 156-159).

The infraorbital nerve (ION) transmits sensory information from mechanoreceptors of the upper lip and vibrissae (whiskers) to the brain via the infraorbital foramen (IOF). Vibrissae are special sensory hairs used by mammals to explore their surroundings. Researchers have used the size of the IOF to infer vibrissa count, which in turn has been incorporated into phylogenetic and ecological interpretations of fossil taxa. However, these interpretations are based on untested assumptions linking IOF size, ION size, vibrissae, and ecology. The purpose of this dissertation is to determine the functional significance of IOF size and to apply the results to the fossil record. It is hypothesized that ecological differences among mammals affects maxillary mechanoreceptivity (touch sensitivity of the rostrum), and that IOF area may be used as a measure of maxillary mechanoreceptivity. Three questions are posed to appraise this hypothesis: (1) Does IOF area correlate with ION area and vibrissa count? (2) How do the IOFs of primates differ from those of other mammals? (3) How do diet, substrate preference, and activity pattern affect IOF size? IOF area, ION area, and vibrissa count were collected from cadaver of extant mammals as well as museum osteological specimens. Results indicate that: (1) IOF and ION areas show a strong positive correlation. Based on this finding, it is hypothesized that IOF area may be a good measure of maxillary mechanoreception. (2) Vibrissae count significantly correlates with IOF area. (3) Euarchontans have relatively smaller IOFs than most other mammals. (4) The IOFs of primates co-vary with diet, where frugivores have relatively larger IOFs than both insectivores and folivores. Infraorbital foramen areas of 14 adapoid, six omomyoid, and 15 plesiadapiform species were measured. Two questions were addressed: (1) Do the sampled fossils share a similar reduction in IOF area to extant primates? (2) Do extinct frugivores have larger IOFs than insectivores and folivores? Results show that, adapoids and omomyoids have relatively small IOFs similar to euarchontans, but plesiadapiforms retain larger IOFs, comparable to most non-euarchontan mammals. Dietary analyses indicate that both frugivorous adapoids and omomyoids have larger IOFs than both insectivorous and folivorous species. / text

Not available / text

The age of the Bridgerian/Uintan boundary has been regarded as one of the most important outstanding problems in North American Land Mammal “Age” (NALMA) biochronology. The Bridger Basin in southwestern Wyoming preserves one of the best stratigraphic records of the faunal boundary as well as the preceding Bridgerian NALMA. In this dissertation, I first developed a chronological framework for the Eocene Bridger Formation including the age of the boundary, based on a combination of magnetostratigraphy and U-Pb ID-TIMS geochronology. Within the temporal framework, I attempted at making a regional correlation of the boundary-bearing strata within the western U.S., and also assessed the body size evolution of three representative taxa from the Bridger Basin within the context of Early Eocene Climatic Optimum. Integrating radioisotopic, magnetostratigraphic and astronomical data from the early to middle Eocene, I reviewed various calibration models for the Geological Time Scale and intercalibration of 40Ar/39Ar data among laboratories and against U-Pb data, toward the community goal of achieving a high precision and well integrated Geological Time Scale. In Chapter 2, I present a magnetostratigraphy and U-Pb zircon geochronology of the Bridger Formation from the Bridger Basin in southwestern Wyoming. The ~560 meter composite section spans from the lower Bridger B to the Bridger E, including the Bridgerian/Uintan NALMA boundary in the uppermost part of the section. Analysis of samples from 90 sites indicates two paleomagnetic reversals that are correlated to an interval spanning Chrons C22n, C21r, and C21n by comparison to the Geomagnetic Polarity Time Scale (GPTS). This correlation places the Bridgerian/Uintan faunal boundary within Chron C21n, during the initial cooling phase following the peak of the Early Eocene Climatic Optimum. Based on the bio- and magnetostratigraphic correlation, I provide correlation of other Bridgerian/Uintan boundary-bearing sections to the GPTS, demonstrating that in the western North America, the Bridgerian/Uintan boundary occurs everywhere in Chron C21n. In addition, U-Pb zircon geochronological analyses were performed on three ash beds from the Bridger Formation. High-precision U-Pb dates were combined with the paleomagnetic polarity data of the same ash beds as well as the integrative chronostratigraphy of the basin to assess prior calibration models for the Eocene part of the GPTS. The data from the Bridger Formation indicate that the Option 3 age model of Westerhold et al. (2008) best reconciles the geochronological data from all of the ash beds except for one. Thus I favor this Option 3 model, which indicates the ages of 56.33 Ma and 66.08 Ma for the Paleocene-Eocene Thermal Maximum and Cretaceous/Paleogene boundary, respectively. In Chapter 3, the body size evolution of three mammalian taxa from the Bridgerian NALMA was analyzed within the context of Bergmann’s Rule, which poses a correlation between the size of endotherms and climate (latitude). The Bridgerian NALMA is from a time of global cooling following the peak of the Early Eocene Climatic Optimum, thus according to Bergmann’s Rule, the Bridgerian mammals are expected to increase in size. This hypothesis is tested among Notharctus, Hyopsodus, and Orohippus, using the size of molar dentition as a proxy for their body size. These taxa represent three different ecomorphs, and I investigated if these taxa showed a pattern of body size change consistent with the prediction made by Bergmann’s Rule, and how their ecological adaptation may have affected their response to the climate change. Prior to analyzing the body size evolution, specimens of Notharctus and Hyopsodus were identified to species based on dental characters. This practice differs from previous studies in which species identification relied on relative size of the individuals and stratigraphic levels of origin. Within the new framework of morphologically determined species identification, five species of Notharctus were recognized, among which, N. pugnax, N. robustior and N. sp. indet. exhibited statistically significant body size increase in the time span of interest. Based on morphological analyses of Hyopsodus dentition, I recognized five species. Dentition-based body size analysis showed that H. lepidus and H. despiciens exhibited a statistically significant change towards larger size within the sampled interval. When analyzed at the generic level, a statistically significant increase was observed for both Notharctus and Hyopsodus. Finally, a genus-level analysis of Orohippus showed a lack of statistically significant size increase over the study interval. Thus, among the three taxa from the Bridgerian, Bergmann’s Rule is supported by Notharctus and Hyopsodus, at least at the genus level, but not by Orohippus, although the patterns are more variable at the intraspecific level. In Chapter 4, 40Ar/39Ar dates were obtained from sanidines from the middle Eocene Henrys Fork tuff and Upper Carboniferous Fire Clay tonstein, with the goal of making highly precise measurements of these two samples, keyed to the Fish Canyon monitor standard. Analytically, both samples were well characterized, as had been shown previously. The irradiation disk was arranged such that there would have been control from the Fish Canyon surrounding each of the unknown pits. However, due to several complications in the lab during the course of the experiment, only the analyses from one run disk (Disk 677) were of the quality needed for the goals of the study. As a result, the Fish Canyon sanidine standards that were irradiated near the center of the irradiation disk had to be discarded, and thus, the neutron fluence could not be mapped out precisely across the entire disk. The 40Ar/39Ar age relative to Fish Canyon sanidines is 47.828 ± 0.205 Ma and 311.937 ± 1.282 Ma for the Henrys Fork tuff and Fire Clay tonstein, respectively (1σ, including error on the age of the monitor). Because the ages were both offset about the same amount, I explored the option of using the U-Pb ID-TIMS ages of the Henrys Fork tuff and Fire Clay tonstein to test the agreement in the chronometers. The Henrys Fork tuff was dated at 48.260 ± 0.107 Ma (1σ, including error on the age of the monitor) using the Fire Clay sanidines and assuming its age is the U-Pb zircon age. The Fire Clay tonstein was dated at 314.593 ± 0.699 Ma (1σ, including error on the age of the monitor), using the Henrys Fork sanidines and assuming its age is the U/Pb zircon age. Although the complications encountered render these data unpublishable, they show great promise as the ages of each sanidine sample, tied to the other ash using the other ash’s U-Pb age, give results that are in close agreement between the two chronometers on the same sample (e.g., 314.593 ± 0.699 Ma vs. 314.554 ± 0.020 Ma at 1σ for sanidine and zircon respectively from the Fire Clay tonstein, and 48.260 ± 0.107 Ma vs. 48.265 ± 0.008 Ma 1σ for sanidine and zircon respectively from the Henrys Fork tuff).

The Queen Charlotte Islands are the most isolated islands in British Columbia and are populated by eight species of indigenous land mammals, all except one of which are represented by at least one endemic form. Geological and botanical evidence lend strong support to the hypothesis that the Islands could have been a refuge to most of these mammals during the last (Vashon) glaciation. Their unique mammal fauna could be the product of insular evolution, or due to the fact that it is of geographical relicts. Absence of fossil material prohibits a final solution to this problem, but circumstantial evidence suggests that the mammals have evolved their unique characteristics as a result of living in an insular environment. This conclusion is reached after the study of the most common mammals living on the Islands; the deer mice (Peromyscus maniculatus keeni and P. sitkensis prevostensis) and the dusky shrews (Sorex obscurus elassodon and S. o. prevostensis), and after a wide literature survey of mammals found on other islands. The most important evidence favouring the insular evolution theory is the uniformity displayed when the characteristics of insular birds and mammals are compared with relatives living on the nearby mainland. Birds living on islands often possess longer tarsi and culmens; artiodactyls, lagomorphs and carnivores tend to be smaller on islands, while rodents are usually larger, live longer and possess shorter tails. A corollary of the relict hypothesis holds that a large reliot rodent can not survive active competition with the smaller form and is displaced by the latter when they come into contact. This theory could not be substantiated by the present study; on the contrary, the two would likely interbreed. The differences between the insular populations of large Peromysous are greater than one would expect if they owed their similarity to a common origin. Finally, the relict hypothesis would hold that such a characteristic as large size is conservative, whereas evidence indicates that this is not generally true. Reasons are suggested for the characteristics which are commonly found in insular mammals and herein lies the most interesting area for future work. / Science, Faculty of / Zoology, Department of / Graduate

The impact of large-scale volcanic eruptions on landscapes can affect many processes ranging from interrupting or redirecting regional soil forming processes and hydrological systems to generating temporary changes in global climate. Though more studies exist every year, less is known of the direct impact of large-scale volcanic eruptions on ecosystems and extinction, while even less is known of their impact on speciation. In deposits throughout the Pacific Northwest a special combination and association of volcanic magnitude with palaeoecological yield frequently presents unique prospects for inquiry. In this study, particular attention is given to large, late Miocene ash-flow tuffs of central and eastern Oregon, the Rattlesnake Tuff among them. Additionally, a scenario is tested whereby populations become isolated from one another across the expanse of ash-flow tuff and enclosed by nearby physical barriers. Exploration into this scenario and the effects of ecological recovery on speciation in mammals are made through a cellular automaton created here and speciation modeling by H.A. Orr. The cellular automaton is validated by a small data set from New Zealand with results of all models compared to studies in ecology, the fossil record, genetics, and island evolution. Results suggest ecosystem recovery is much faster than mammalian species origination rates. Though evolution in mammals is known to occur over relatively short intervals of time (10 - 10 yrs), based on model comparisons, primary productivity generally returns to its carrying capacity two orders of magnitude (10 - 10 vs. ≥ 10 yrs) faster than mammalian speciation.

Thesis (PhD (Archaeology))--University of Stellenbosch, 2005. / This study investigates the evolution of modern mammalian faunas in the central interior of southern Africa by testing the hypothesis that the evolution of the black wildebeest, Connochaetes gnou, was directly associated with the emergence of Highveld-type open grasslands in the central interior. Southern Africa can be distinguished from other arid and semi-arid parts of the continent by the presence of an alliance of endemic grazing ungulates. The black wildebeest is characteristic of this alliance. Open habitats are essential for the reproductive behaviour of the black wildebeest, because territorial males require an unobstructed view of their territories in order to breed. The specialised territorial breeding behaviour of the black wildebeest is the reason why the black wildebeest is historically confined to the Highveld and Karoo areas and why it is reproductively isolated from sympatric blue wildebeest, Connochaetes taurinus. The finds from a number of fossil-rich localities, dating from the recent past to approximately a million years ago, have been identified. The remains referred to ancestral C. gnou have been subjected to detailed qualitative and quantitative osteological comparisons with cranial and post-cranial elements of modern and fossil reference specimens. This material includes extant southern African alcelaphines and fossil materials of C. gnou, the extinct giant wildebeest, Megalotragus priscus, and North African fossil alcelaphines. The results show that cranial changes in fossil C. gnou, particularly the more forward positioning of the horns, basal inflation of the horns and the resultant re-organisation of the posterior part of the skull, preceded other skeletal modifications. These cranial changes indicate a shift towards more specialised territorial breeding behaviour in the earliest ancestral black wildebeest, evident in the specimens of the c. million year old Free State site of Cornelia-Uitzoek. Since the territorial breeding behaviour of the black wildebeest can only function in open habitat and since cranial characters associated with its territorial breeding behaviour preceded other morphological changes, it is deduced that there was a close association between the speciation of C. gnou from a C. taurinus-like ancestor and the appearance of permanently open Highveld-type grasslands in the central interior of southern Africa. This deduction is supported by the lack of trophic distinction between the modern black and blue wildebeest, suggesting that the evolution of the black wildebeest was not accompanied by an ecological shift. It is concluded that the evolution of a distinct southern endemic wildebeest in the Pleistocene was associated with, and possibly driven by, a shift towards a more specialised kind of territorial breeding behaviour, which can only funtion in open habitat. There are significant post-speciation changes in body size and limb proportions of fossil C. gnou through time. The tempo of change has not been constant and populations in the central interior underwent marked reduction in body size in the last 5000 years. Vicariance in fossil C. gnou is evident in different rates of change that are recorded in the populations of generally smaller body size that became isolated in the Cape Ecozone. These daughter populations, the result of dispersals from the central interior, became extinct at the end of the Pleistocene.