The dissertation research presented herein addresses two questions on possible ecological drivers of mammalian diversity dynamics at macroevolutionary time scales. The first question is whether key intrinsic biological traits that are tightly correlated with body size (e.g., reproductive rates) have strong influence on the extinction probability of mammalian taxa at the generic level. The second question is whether, within a regional mammalian fauna, the ecological composition of carnivores (as inferred from their dental morphology) responds in predictable manners to shifts in the ecological composition of non-carnivores that represent their potential prey.

In preparation for the ecological analyses of carnivore and non-carnivore compositional changes through time, concentrated effort was made to advance the taxonomy of carnivorous mammals from the middle Eocene of southern California. As part of this effort, the first chapter describes a carnivoramorphan that sheds a new light on the origin and early evolution of crown-group carnivorans. The new taxon, Lycophocyon hutchisoni, exhibits stages of dental and basicranial evolution that are intermediate between earlier carnivoramorphans and the earliest representatives of canoid carnivorans. The evolutionary affinity of the new taxon was determined by a cladistic analysis of previously-published and newly-acquired morphological data for 30 Paleogene carnivoramorphans. The most-parsimonious trees identified L. hutchisoni as a basal caniform carnivoran, and placed (1) Tapocyon robustus, Quercygale angustidens, "Miacis" sylvestris, "M." uintensis, and "M." gracilis inside or outside the Carnivora, (2) nimravids within the Feliformia, and (3) the amphicyonid Daphoenus outside the crown-group Canoidea. Parsimony reconstructions of ancestral character states suggest that loss of the upper third molars and development of well-ossified entotympanics that are firmly fused to the basicranium (neither condition is observed in L. hutchisoni) are not associated with the origin of the Carnivora as traditionally thought, but instead occurred independently in the Caniformia and the Feliformia. A discriminant analysis of the estimated body weight and dental ecomorphology predicted a mesocarnivorous diet for L. hutchisoni, and the postcranial morphology suggests a scansorial habit. Thus, Lycophocyon hutchisoni illuminates the morphological evolution of early caniforms leading to the origin of crown-group canoids. Nevertheless, considerable uncertainty remains with respect to the phylogenetic origin of the Carnivora. The minimum date of caniform-feliform divergence is provisionally suggested to be either 47 million years ago or 38 million years ago, depending on the position of "Miacis" sylvestris within or outside the Carnivora, respectively.

The second chapter investigates the relationship between body size as a proxy for various intrinsic biological traits of key importance and extinction probability as measured by durations of genera in the fossil record. Preservation of mammalian diversity requires a concentrated effort to identify biological correlates of vulnerability to environmental perturbations. Studies of living mammals and late-Quaternary extinctions frequently point to large body size as a correlate--if not necessarily a determinant--of elevated extinction risk in mammalian species, and this correlation is often attributed to slow reproductive rates and lower population densities of large taxa. At the same time, biological patterns of extinction risk above the level of species have received much less attention, despite their relevance to conservation of evolutionary history embedded in ecological types that are more inclusive than individual species. I examined the North American fossil record of modern and some extinct families of terrestrial mammals to test whether extinction probability (or, more precisely, inter-regional extirpation probability) of genera, as measured by their durations in geologic time, scales with body size across 7 orders of magnitude in body weight. After adjusting observed generic durations for significant paleontological sampling bias against small taxa, generalized least-squares regression analyses showed no correlation between estimated body weights and durations in 221 Oligo-Pleistocene genera ranging from shrews to rhinoceroses. The same lack of correlation was observed for subsets of the data that (a) approximated basic trophic divisions (small/large herbivores, "insectivores," and carnivores) or (b) were grouped by the timing of extinctions, suggesting that the overall pattern is not clouded by trophic and temporal variations in the relationship between size and vulnerability. The only notable deviation from this pattern was the significantly shorter durations of carnivorans compared to other taxonomic/ecological groups. Qualitatively identical results were obtained by analyses of durations and inter-birth interval lengths expected from body weights. Thus, in general, the population-biological expectation of higher extinction risk for large and slow-reproducing mammals was not supported for the genera that lived prior to significant anthropogenic influence. Two non-exclusive hypotheses are offered to explain this apparent mismatch: (1) the size-biased extinctions since the late Quaternary and elevated extinction risk for living large mammals signify an abnormal state of diversity dynamics brought about by human-induced reduction of large-mammal populations to critical levels, below which demographic or environmental stochasticity alone can threaten slow-reproducing taxa of low population density; (2) large mammalian species indeed have higher probabilities of extinction, but replacement of lost species within genera compensates for this pattern, resulting in comparable durations of large and small taxa at the genus level. The corollary of the first hypothesis is that, in normal times, thriving large mammals are no more likely--and perhaps less likely--to reach the critical population size than small mammals. The second hypothesis, if true, would indicate that extinction processes are distinct across levels of phylogenetic hierarchy and that prediction of future extinctions at supraspecific levels should not simply rely on extrapolation of extinction risk for individual species, especially if some of the species constituting a genus of interest are poorly known.

Building on the taxonomic work on the middle-Eocene carnivores of southern California, I investigate in the final chapter the matches and mismatches between shifts in the ecological compositions of mammalian carnivores and other mammals that constitute their potential prey at the macroevolutionary time scale of approximately 6-9 million years. The middle-Eocene fossil record of southern California, which includes a diverse array of carnivores and particularly rich record of small mammals, was analyzed. Appearance event ordination was used to estimate the relative ages of fossil-bearing localities and their associated assemblages. Using the predicted temporal ranges of carnivore taxa and locality-level occurrence data for non-carnivores (ultimately grouped into time bins), it was found that changes in the distribution of taxa, and possibly taxonomic abundance as well, across morphological categories (defined by estimated body weight, arboreal versus non-arboreal habit, and ecologically-informative dental morphology) are largely discordant between carnivores and non-carnivores in the study system, except for the overall increase in the number of taxa in both groups. Analysis of morphological-compositional variation and factors that correlate with taphonomic disparity lend support to the interpretation of observed diversity fluctuations through time in non-carnivores. The findings raise additional questions about the controls of carnivore diversity--for example, what promotes the appearance of new morphotypes--and predictability of their extinctions.

To provide empirical evidence of species boundaries and the role of climatic change in affecting evolution, we documented evolution of the sagebrush vole, Lemmiscus curtatus, through hundreds of thousands of years by following populations from the middle Pleistocene to the present. We found that: (i) extant representatives of the species culminate a morphological transition that was initiated within an unusually and and warm interglacial period, perhaps related to the shift from glacial-interglacial cycles dominated by a 41 000 year periodicity to those dominated by a 100 000 year rhythm; and (ii) sympatry of extant and extinct morphotypes persisted for more than 800 000 years. This exceptionally detailed tracing of extinct populations into extant ones suggests that species such as the one we studied are real entities in space, that their boundaries become fuzzy (although potentially diagnosable) through time and that unusual climatic warming may initiate significant evolutionary change manifested at the morphological level.

Anticipating how species and ecosystems will react to continued climate change is of critical importance to biodiversity conservation and to management of the ecosystem processes on which we rely. Identifying how individual species in a community have responded in the past can be accomplished by evaluating the fossil record on a local and/or regional scale, and by examining spatial patterns of modern abundance and diversity. Here, I explore regional patterns of mammal diversity across the Colorado Plateau (CP), examine local small mammal diversity fluctuations in fossil deposits from northern San Juan County, Utah, through the late Holocene, and assess modern spatial diversity patterns across a range of San Juan County sites.

Over the past century, extraordinary global transformations have taken place, including climate change and land conversion for human use. With these unusually rapid and extreme global changes underway, it is increasingly important to understand the extent to which designated conservation areas have protected biodiversity thus far, and to gauge their potential for continuing to do so in the future. Chapter 1 examines the efficacy of biodiversity preservation in National Park Service (NPS) lands of the CP by using analysis of nested species assemblages to compare surveyed mammal communities to the range map predictions of which species should be present. I find that NPS lands are nested, and, although site diversity is correlated with area, elevational range, budget and visitation, a comparison between species lists compiled from surveys versus range map distributions reveals that the biogeographic patterns prevailing today cannot be distinguished from those prevailing when these NPS sites were established. These broad-stroke patterns define an important context in which to direct future conservation efforts as we attempt to divert and mitigate anthropogenic impacts—past, current, and future.

Modern patterns of diversity are the result of past events and processes that take place on the scale of decades, centuries, and millennia. Detailed paleoecological records from Quaternary deposits are remarkably useful in characterizing these long-term ecological dynamics, but only a handful of Quaternary localities that sample the small mammal community of the CP have been studied to date. In chapter 2, I describe my excavation and analyses of two fossil-bearing alcoves, East Canyon Rims 2 (ECR2) and Rone Bailey Alcove (RBA) (San Juan County, Utah), and quantify diversity and abundance change of the small mammal community as recorded in the fossil samples. Fossil localities with comparable mammal diversity have not been reported from this region previously, so these sites provide novel insight into Holocene mammal diversity in southeastern Utah. Further, these localities contribute to our understanding of natural variation in this system by providing faunal data for a period of recent climate change—cool-wet to warm-dry. AMS radiocarbon dates on 33 bone samples from these sites span ~4.4 ka-present, and shed light on pre-industrial faunal dynamics in the region over the course of environmental change, most notably aridification. I test for an effect of climate on community evenness and relative abundance of 10 small mammal taxa—leporids, perognathines, small sciurids, arvicolines, Cynomys, Neotoma, Dipodomys, Onychomys, Peromyscus, and Thomomys—and find that, in spite of considerable increases in aridity and temperature, neither is significantly correlated with relative abundance or evenness when statistically tested, but there are qualitative patterns consistent with a response to increasing aridity around 1000 years ago.

The CP is home to a diverse complement of species that are experiencing increasing temperature and drought stress today. Understanding how mammal communities might be expected to respond to impending global changes requires a baseline of information on presence, abundance, and spatial variation of species on the landscape today. Chapter 3 describes the results of a preliminary analysis of spatial variation in the small mammals of northern San Juan County at a single point in time, with the objective of learning how species commonly preserved in the fossil record sort geographically in relation to variation in their abiotic environment. I conducted mark-recapture surveys at 8 sites in northern San Juan County, two of which were located in the immediate vicinity of ECR2 and RBA. Over the course of one year, I compiled abundance and presence/absence data on nine species: Neotoma albigula, Onychomys leucogaster, Peromyscus maniculatus, P. truei, Dipodomys ordii, Perognathus flavescens, P. parvus, Ammospermophilus leucurus, and Tamias rufus. In chapter 3, I evaluate spatial differences in species richness using occupancy modeling and metrics of taxonomic difference, and I assess proportional and rank abundance across sites. Although the results are preliminary, some patterns are emerging: sites spanning 50km and 550m elevation range sample the same small-mammal species pool, but abundance of those species varies non-randomly, and sites are less similar in abundance than expected by random distribution of individuals. Species evenness varies among sites, and sites with low evenness are dominated by Peromyscus maniculatus, a “weedy” species with broad habitat requirements. This is also the first report of Perognathus parvus east of the Colorado River, suggesting recent range expansion of the species. Occupancy models indicate that presence/absence of different species is determined by different aspects of their environment, and therefore species will respond idiosyncratically to future environmental changes. However, more survey data is necessary before these patterns can be considered robust or fully explained.

In chapter 4, I compare fossil diversity at ECR2 and RBA to modern diversity at the same sites. I find that evenness reached a peak in ECR2 and RBA between ~1-1.7 ka, then began to decline between ~0.7-1 ka. Evenness of the modern community at ECR2 and RBA is also significantly lower than in the fossil record between ~0.7-4.5 ka. The observed drop in evenness occurred prior to the onset of high-impact, post-European human land uses, like livestock grazing, and is coincident with the time when Ancestral Puebloan populations crashed due to long-term periodic droughts, suggesting a marked environmental change between ~0.7-1 ka. Low modern evenness is consistent spatially—modern evenness at all survey sites is lower than it is for all fossil time bins ~0.7 ka and older, suggesting that this was a landscape-level decline in diversity. These results send a cautionary message: though the basic taxonomic integrity of the small mammal community is still present, abundance and community structure are very different today.

Additional information on past and current diversity of the CP will improve forecasting and establish baselines against which to compare future surveys, allowing us to gauge rates and direction of change, and to prioritize conservation efforts in the future. This study emphasizes the enormous utility of the fossil record in understanding the extent of ecological fluctuations that can be considered “normal” through long periods of time, information which is essential as we struggle to conserve biodiversity in a rapidly changing world.

Abstract

Late Quaternary Megafaunal Extinctions in South America:

Chronology, environmental changes and human impacts at regional scales

by

Natalia Andrea Villavicencio Figueroa

Doctor of Philosophy in Integrative Biology

University of California, Berkeley

Professor Anthony D. Barnosky, Chair

By the end of the Pleistocene the world lost most of its species of large mammals in what is known as the Late Quaternary Extinction event. The debate about the possible causes of extinction revolves around the impacts caused by modern humans migrating around the world, the climate changes associated with the glacial-interglacial transition happening at the time of the extinction and combinations of both. South America was one of the most severely impacted continents losing over eighty percent of all its species of mammals with an average body weight exceeding forty four kilograms. In this continent, human arrival and late glacial climate changes were not far separated in time and previous analyses have shown interesting regional differences in the timing and pattern of extinction inside the continent.

A critical step to understand the extinction event at regional and continental scales is the development of robust radiocarbon-based chronologies of megafaunal presence and extinction which can be compared to the timing of arrival of humans and of environmental changes. This dissertation addresses the Late Quaternary Extinction event debate in South America by developing analyses of the extinction at regional scales, and improving the chronology of extinction for some regions of the continent by radiocarbon dating bone specimens of extinct megafauna following high standard procedures for radiocarbon dating bone.

Chapter one consists of a bestiary of the Pleistocene megafauna of South America. It describes each species and genera of megafauna giving details about their geographic distribution and general paleoecology. A final synthesis of the information shows regional differences in megafaunal diversity that can be explained by sampling bias. While regional differences in diversity persist in time when the Late Pleistocene is compared to the present, regions are today more similar than in the past, which suggests that a considerable amount of regional megafaunal endemism was lost during the Late Quaternary Extinction event.

Chapter two is a regional scale analysis of the megafaunal extinction in Southern Patagonia. Using published information it was possible to build a robust chronology of magefaunal extinction and human arrival into this region. When comparing these chronologies with the timing of major environmental changes it seems that a combination of human impacts and vegetation changes were behind most of the megafaunal extinctions.

Chapter three describes the process of radiocarbon dating bone specimens of extinct megafauna following high-standard procedures of bone treatment. It was possible to produce fifty four radiocarbon dates from which twenty seven are reported in this chapter. The new data improves the chronology of extinction for some areas, particularly for the Central Andes and for Southern Chile. These new chronologies of extinction showed that in the Central Andes extinct megafauna disappears at the time of human arrival while the megafauna present in Southern Chile coexisted with humans for thousands of years. In the second case the megafaunal extinction happens at a time of major environmental changes. These differences highlight the need of developing regional analyses, rather than continental-scale analyses, in order to have a more comprehensive understanding of the extinction event in South America.

Asphaltic deposits, or "tar pits," present a unique opportunity to investigate the paleobiology and paleoecology of Quaternary mammals due to their tendency to accumulate and preserve remains of numerous taxa, along with associated materials that can aid in paleoenvironmental and chronological analyses. This role is especially important in areas with low preservation potential or incomplete sampling, such as the Neotropics.

Fossil deposits in the asphaltic sediments of the Santa Elena Peninsula in southwestern Ecuador contain some of the largest and best-preserved assemblages of Pleistocene megafaunal remains known from the neotropics, and thus represent an opportunity to greatly expand our knowledge of Pleistocene paleoecology and the extinction of Quaternary megafuana in this region. This dissertation reports data from excavations at Tanque Loma, a new late-Pleistocene locality on the Santa Elena Peninsula that preserves a dense assemblage of megafaunal remains in hydrocarbon-saturated sediments along with microfaunal and paleobotanical material.

Chapter 1 details the results of three years of excavations and associated sedimentological, stratigraphic, systematic, taphonomic, and chronological studies at Tanque Loma. Remains of extinct Pleistocene megafauna are encountered within and up to one meter above a laterally extensive asphalt-saturated sandstone layer along with abundant plant material. Several meters of presumed-Holocene sediments overlying the megafauna-bearing strata are rich in microvertebrate remains including birds, squamates, and rodents, most likely representing raptor assemblages. While over 1,000 megafaunal bones have been identified from the Pleistocene strata at Tanque Loma, more than 85% of these remains pertain to a single species, the giant ground sloth Eremotherium laurellardi. Only five other megafauna taxa have been identified from this site, including Glossotherium tropicorum, Holmesina occidentalis, cf. Notiomastodon platensis, Equus (Amerhippus) santaelenae, and a cervid tentatively assigned to cf. Odocoileus salinae based on body size and geography. No carnivores have yet been identified from Tanque Loma, and microvertebrate remains are extremely rare in the megafauna-bearing deposits, although terrestrial snail shells and fragmented remains of marine invertebrates are occasionally encountered. Accelerator Mass Spectrometry radiocarbon dates on Eremotherium and c.f. Notiomaston bones from within and just above the asphaltic layer yielded dates of around 17,000 - 23,500 radiocarbon years BP.

Taken together, the taxonomic composition, taphonomy, geologic context, and sedimentology of Tanque Loma suggest that this site represents a bone bed assemblage in a heavily vegetated, low-energy riparian environment with secondary infiltration of asphalt that helped preserve the bones.

The large accumulation of one taxon, Eremotherium laurillardi, at Tanque Loma offers a unique opportunity to investigate the ecology and behavior of this species. Chapter 2 uses data from this and other paleontological localities as well as modern African ecosystems to investigate the formation of the E. laurillardi assemblage at Tanque Loma and the behavioral ecology and life history of this species. Multiple lines of evidence, including a monodominant taxonomic composition; a multigenerational age structure with prime adult individuals well-represented; sediments suggestive of a low-energy anoxic aquatic environment; and the presence of abundant plant material that appears to pertain to coprolites of E. laurillardi; suggest that these sloths congregated and died in a protracted mass mortality event in a marshy riparian habitat. The evidence is consistent with a mass death due to drought and/or disease in a shallow watering hole, paralleling situations observed among large wallowing herbivores in Africa today. Furthermore, several neonate and fetal individuals are present in the deposit, suggesting that this species may have had a distinct breeding season, which is also common among large herbivores in seasonally dry tropical environments.

Chapter 3 endeavors to offer context for the Tanque Loma locality by combining data from these excavations with analyses of other asphaltic vertebrate localities in the region. The most well known asphaltic paleontological locality in tropical South America is the Talara tar seeps in northwest Peru, which has yielded a great diversity of microfossils as well as extinct megafauna. In addition, two other highly productive asphaltic localities have been excavated on the Santa Elena Peninsula -- the La Carolina locality excavated by Robert Hoffstetter in the 1940's, and the Coralito locality excavated by Franz Spillmann in the 1930's and A. Gordon Edmund in the 1960's. I examined fossils from these excavations currently housed in the collections of the Museo Gustavo Orces in Quito, Ecuador, the Royal Ontario Museum in Toronto, Canada, and the Museum National d'Histoire Naturelle in Paris, France, in order to compare the depositional and environmental contexts of these different sites and to investigate the paleoecology and biogeography of the mammal taxa preserved therein. In general, the communities of megaherbivores are comparable between these geographically close sites, but Talara and La Carolina present a much more diverse assemblage of birds, micromammals, and carnivores as compared with the other two localities. Taxonomic, geomorphological, and taphonomic data indicate that these two sites were most likely "tar pit" style traps analogous to the famous Rancho La Brea locality in California, USA, while the SEP sites Coralito and Tanque Loma likely represent fossil assemblages in marshy or estuarine settings with secondary infiltration of tar. In addition, geological and taxonomic differences between the nearby localities Coralito and Tanque Loma suggest differences in local paleoenvironments and lends further support for the hypothesis of gregarious behavior in at least two species of extinct giant ground sloths.

Finally, the radiocarbon dates so far obtained on extinct taxa at Tanque Loma and the other asphaltic localities examined here are consistent with a model positing earlier extinctions of megafauna in tropical South America than of related taxa further south on the continent, although this observed pattern may be an artifact of low sampling in the region.

Megafauna are ecologically important. They are ecosystem engineers that substantially modify modern ecosystems, and likely did so for prehistoric ecosystems prior to the Late Quaternary extinction (LQE) event as well. The LQE resulted in the loss of ~65% of all large mammals during an age of global climate change and human population expansion. This means that understanding the causes and ecological impacts of megafauna preceding, during, and following the LQE is important for better understanding megafauna ecology and conservation today.

To further this understanding, here I 1) explore the developing body of indicators used for inferring historic and prehistoric megafauna abundances; 2) investigate the environmental conditions surrounding human arrival and megafauna extirpation in Brazil, and; 3) test how sensitive the Sporormiella megafauna indicator is to temperature and humidity, as these factors could confound megafaunal population-size estimates based on Sporormiella abundances.

The first chapter reviews the many different population-size indicators used in megafauna paleoecology. and finds all have their pros and cons regarding their applicabilities towards reconstructing megafauna populations depending on the depositional environment and other taphonomic factors. A widely used indicator of relative megafauna population size is the abundance of the dung fungus Sporormiella in sediment records, despite the need for more taphonomic work necessary to more robustly relate spore abundance to megafauna abundance.

The second chapter untangles the relationship between climate, vegetation changes, human population growth, and megafauna decline surrounding the LQE in Brazil as a case study. I found that combinations of anthropogenic, climatic, and vegetational changes are likely implicated as causal factors, but the tree factors vary in their importance for different regions of Brazil. However, human population growth prior to the megafauna extirpation stands out as most notable.

The third chapter reports results of an experiment that tested the effects of temperature and relative humidity on Sporormiella growth. I found that humidity above 89% does not notably affect Sporormiella growth but temperature in the range of 10-40 o C is important.

In sum, this means that there is room for development of megafauna indicators, nuances between how different LQE causes can be distinguished at finer spatial scales, and reason to suggest that past climate change may bias Sporormiella -based reconstructions of megafauna populations.

The paleontological record of mammals offers many examples of evolutionary change, which are well documented at many levels of the biological hierarchy-at the level of species (and above), populations, morphology, and, in ideal cases, even genes. The evolutionary changes developed against, backdrop of climatic change that took place on different scales, from rapid shifts in climate state that took only a few decades, to those that occurred over a millennial scale, to regular glacial-interglacial transitions with cycles of roughly a hundred thousand years, to long-term warming or cooling trends over hundreds of thousands to millions of years. Are there certain scales of climatic change that accelerate evolution? And what will the current global warming event do to evolutionary rates? Here we use paleontology-the study of fossils-to illustrate the scientific method behind answering such complex questions, and to suggest that current rates of global warming are far too fast to influence evolution much and instead are likely to accelerate extinctions.

Understanding species-environment interactions through time is important for studying evolutionary processes such as taxonomic turnover. Studying this ecological interaction in the past sets a baseline for expected changes to occur given future environmental changes. Here I study species-environment interactions at the local and continental scale to understand how faunal composition, dietary niches, and climatic niches of species shift during periods of climatic and environmental change. A thorough revision of the Barstovian Mascall Fauna in Oregon provides an up-to-date faunal list and new ages for tuffs in order to examine faunal change at a local scale across a major climatic event, the mid-Miocene Climatic Optimum. Fifteen species are added and six synonymies are incorporated into the original faunal list. The Mascall Tuff, the most fossiliferous layer of the Mascall Formation, is dated at 15.3 Ma and the Kangaroo Tuff in the upper unit of the formation is dated at 13.6 Ma. Faunal comparisons to other Barstovian localities in North America reveal patterns of provinciality during this time. Faunal composition is consistent through the formation except for a turnover from browsing to grazing equids.

To examine this turnover in more detail, the dietary niches of four equid genera are reconstructed using stable carbon isotopes. Dietary niche partitioning is evident based on 13C values and tooth morphology: Archaeohippus was a small brachyodont equid with a narrow dietary niche most likely consuming crown leaf vegetation in the clearings of a woodland habitat; Parahipppus and Desmatippus were medium sized browsing equids with a broad dietary niche eating C3 browse in an open environment; and aff. Acritohippus was a larger grazer also with a broad dietary niche eating C3 grasses in an open environment. The dietary niches of these four genera did not change through time across the mid-Miocene Climatic Optimum. Extinction of the browsing genera, especially Archaeohippus with its narrow niche breadth, is most likely to do opening of habitats as C3 grasses spread after the mid-Miocene Climatic Optimum. There is no evidence of C4 vegetation in the diet of aff. Acritohippus suggesting it was not a dominant part of the vegetation in the Pacific Northwest during the Barstovian, in contrast to other regions of North America during that time.

Although the most common method of reconstructing niche space of extinct mammals is using stable isotopes to reconstruct their dietary niche, given other potential environmental proxy data, a more complete niche space of a species can be reconstructed in the fossil record. It is often difficult to obtain sufficient data to reconstruct entire environmental layers to study niche dynamics through time but proxy data can be obtained to examine the species niche in multivariate space. I test the potential for using this data to test for niche instability through time by studying the climatic niches of 15 mammalian species from the Last Glacial Maximum to the Recent. I find evidence supporting species niche shifts, primarily along the temperature axis, however the shifts are not greater than the shift in climate from the Last Glacial Maximum to the Recent. Therefore, species are shifting their realized niche space and are not evolving their fundamental niche space. When studying niche dynamics in multivariate space in the fossil record, tests for realized niche stability are possible, however tests for niche evolution require background environmental layers and information on the size and shape of the fundamental niche space.

Dramatic climate changes are already occurring, yet their ecological impacts remain difficult to predict as we lack both a detailed understanding of how key indicator species will react as well as large-scale models that are ground-truthed using paleontological data. In my dissertation, I focused on these challenges. I examine how climate change not only changes species' size and range, but can elicit evolutionary responses in phenotype and alter population variation. Detailed reconstructions of species' paleontological ranges test predictions made by species distribution models (SDMs) as well as their underlying assumptions. Population-level analyses of shifts in morphological variation through time allow the prediction of future evolutionary responses and the assessment of susceptibility to environment stress due to reduced natural variation. I focus on the how climate changes might affect California's ecosystems, developing quantitative methods to look at how morphological shape changes across space and through time in ecologically important small mammals, Microtus (voles). Looking back at their response to paleoecological transitions, I make predictions about how they might react in the future.

In Chapter 1, I use geometric morphometrics of vole dentition to establish a potential new paleoclimate proxy. First, I test if Microtus morphology correlates with paleoclimate signals, using an abundant California species, Microtus californicus. Geometric morphometrics (quantitative shape analysis) and partial least squares (PLS) analyses reveal geographic signals in the shape of the first lower molar (m1) of this species. M. californicus m1s are relatively straight in the northwest, cooler, moister portion of California and more curved in the southeast, hotter, drier portion of the state. These tooth shape changes may be a result of selection related to different vegetation ultimately controlled by climate, and therefore diet, within the species' range. The pattern in m1 shape persists when phylogeographic hypotheses are taken into account, indicating that the climate signal is significant independent of intraspecific groupings. This method reveals a geographic/climatic signal linked with morphological variation across the range of M. californicus and adds an important proxy to reconstruct past climates at fine spatiotemporal scales.

Another challenge addressed in my dissertation is that of species-level identification of fossils, which is necessary to maximally interpret the biostratigraphy, evolution, and paleoecology of Quaternary vertebrate localities. Microtus fossils typically are preserved only as isolated teeth, making identification difficult. In Chapter 2, I distinguish between the five species of Microtus living in California today (M. californicus, M. longicaudus, M. montanus, M. oregoni and M. townsendii) using geometric morphometrics on only their m1. Discriminant analysis on the resulting projected shapes correctly classifies extant specimens of known species 95 percent of the time, enabling vole identification from several important Quaternary fossil localities. In addition, I demonstrate the importance of using jackknife metrics for evaluating discriminant analyses and make some initial identifications that recognize the first extralimital fossil Microtus specimens in California.

Using the identification methods established in Chapter 2, I then trace range shifts in Pacific-coast Microtus species throughout the Quaternary. I reinterpret fossil localities that contain Microtus specimens and compare Quaternary range change to patterns of species' range shifts over the last 100 years. I find range contractions in all five species examined, but individual congeners react differently and to different climate variables. Using these detailed range reconstructions based on newly identified fossils, I examine whether SDMs projected into the past can predict that past habitats would have been suitable for the fossils found therein. I find that nearly half of the extralimital fossil specimens, those fossils found outside the modern range of the species, are living in habitats in the past that were predicted by the SDMs. The species that are not predicted by the SDMs all have niche reconstructions that are strongly influenced by precipitation, leading to the hypothesis that paleoclimate reconstructions may be incorrectly modeling precipitation variables. In addition, I find that two species of Microtus reacted similarly to climate change earlier in the Quaternary as they have over the last 100 years. Although one species, M. longicaudus, has experienced much more rapid range contraction 100 years than previously in the Quaternary.

In my final chapter, I trace morphological variation in M. californicus m1s through time and across California over the last 45 ky. I compare the effects of climate change on this species at the population and species levels. I find that m1 shape is significantly correlated with mean annual precipitation in this species. As California has become increasingly arid, M. californicus appears to have lost some of the m1 variation that is correlated with high-precipitation climate regimes. Although, at the species level I have yet to see any evidence that climate change has resulted in a change in Quaternary range limits. However, future climate change is likely to stress the species to the extent that populations in increasingly wet or dry habitats may be extirpated.

Throughout my dissertation, I demonstrate the utility of using detailed paleontological data in examining the past and future effects of climate change. In being able to identify fossil specimens to the species level, we can begin to directly compare modern and paleontological ecology studies. Using those identifications, we can create accurate paleorange reconstructions that can be used to test predictive distribution models and explore the underlying factors maintaining range limits. Once a species is identified, high-resolution quantification of morphological features, such as teeth, using geometric morphometrics can allow us to trace shifts in variation through time. This allows us to see the history of a species variation so that we can determine whether it retains enough variation to react to future stress.

A Review of New Testudine Specimens from the Oligocene and Miocene of the Great Plains of North America, Including Descriptions of Two New Taxaby Eric M Holt Doctor of Philosophy in Integrative Biology University of California, Berkeley Professor Emeritus Anthony D Barnosky, Chair

The fossil record of Testudines in North America is well known for some parts of the Tertiary period, but for many stages representing millions of years our knowledge of Testudine diversity is both poor and outdated. The gaps in knowledge are pronounced for the Oligocene and Miocene in North America, despite an abundant fossil record. This study begins to address the gap in our understanding of fossil turtles by utilizing existing museum specimens from the Great Plains and adjacent Rocky Mountain basins, the majority of which have not been previously identified beyond the ordinal level. Updated identifications based on fossil shells are provided and the morphological criteria for recognizing many taxa are clarified, despite there being a bias in museum collections towards subadult and juvenile testudine specimens. A previously unknown regional variant of Gopherus edae is described, and initial steps are taken toward documenting the range of intraspecific morphological variation found within various taxa of Oligopherus, Gopherus, Stylemys, and Hesperotestudo. Chapter One lays the groundwork for future studies on tortoise diversity through time and space, and the relationship between their evolution, distribution, and climate change.

In Chapter Two the largely complete shell of a new species of tortoise, Hesperotestudo nicholsorum n. sp., is described from Lemhi County, Idaho, USA. The tortoise genus Hesperotestudo Williams, 1950b, was widespread throughout North America from Canada to El Salvador from the earliest Miocene to the late Pleistocene but retains no extant members. The specimen was collected from Late Hemingfordian (~15-16.3 Ma) sediments in the Railroad Canyon Sequence of the Sixmile Creek Formation. Previous studies have established a late Eocene paleoelevation of 3.7 km for the area. Elevational decrease due to Basin and Range extension did not happen until the middle Miocene, indicating that the fossil locality was higher in the Hemingfordian than the roughly 2 km elevation it is today. This makes H. nicholsorum both the highest elevation specimen of Hesperotestudo currently described and one of the oldest members of its genus. The new taxon shares many morphological similarities with other Hesperotestudo but also exhibits characters more commonly found in Gopherus.

In Chapter Three I describe the shell of another new tortoise, Hesperotestudo niobrarensis n. sp., from Cherry County, Nebraska, USA. The specimen was collected in 1933 from Clarendonian sediments in the Ash Hollow Formation of the Ogallala Group. An isolated left epiplastron from the Clarendonian Ash Hollow Formation near Merrit Reservoir in Cherry County, Nebraska is referred to the new species. This new taxon shares many morphological similarities with other Hesperotestudo but also exhibits a unique combination of characters not found in other members of the genus.