The early Pliocene age Gray Fossil Site (GFS) is a fossil site that preserves diverse fauna and flora and represents one of only a few sites of its age in eastern North America. The assemblage of fauna found at GFS is unique compared to what has been found at other contemporaneous fossil sites across the continent. While studies of the fauna and flora have helped us to understand the ecosystem at GFS, detailed study of the diverse mammal community will help us better understand this unique site. Studying mammalian community structures at fossil sites can provide an abundance of information about the past such as, ecological inferences and climate conditions. To understand the paleoenvironment at GFS, I have gathered data from twenty modern communities and five well-known contemporaneous sites. Mammal species from each of these 26 sites have been categorized by body size, locomotor mode, and cheek tooth crown height to characterize the niches occupied by each species. Proportions of species within categories have been compared and analyzed across modern and fossil sites using discriminant function analysis (DFA). Results of the DFA demonstrate that modern communities with different climates and habitats can be distinguished based on the body size, locomotion, and cheek tooth crown heights of mammals living there. Moreover, functions can be used to infer conditions of past sites. Species diversity within categories was also compared across all sites. Results show that GFS has more brachydont and scansorial species present, and fewer cursorial species than occur at other contemporaneous sites. The results of the discriminant functional analysis indicate that the GFS community structure is most similar to modern temperate forest regions of the Himalayan Mountains in China and modern Washington Co., TN. Proportions of brachydont, gliding, and scansorial species appear to be driving variables behind these results.

The skin is the largest organ of the body and provides many functions. Among tetrapod vertebrates, amphibian skin is semi-permeable and responsible for a greater proportion of water absorption and gas exchange. Myriad factors affect the physiological performance of amphibian skin. Morphological traits linked with amphibian skin physiology or ecology have remained difficult to discern because of a lack of quantitative comparative research and the discovery of sources of intraspecific variation that are mostly ignored in study designs. This thesis aims to address the effects of these sources of variation using a trait that is known to vary between sexes, among seasons, and among body regions and thought to be linked with physiology or ecology, skin thickness. The first source of variation addressed is sexual dimorphism. Specimens of the white-lipped treefrog, Litoria infrafrenata, that display sexual dimorphism in body size and skin thickness were used to test if body size was the main determinate of sexually dimorphic skin thickness. Size corrected values did not significantly differ between males and females, although the sample size was small. Seasonal variation in skin thickness has also been documented in some species, so the American bullfrog (Lithobates catesbeianus), the Northern leopard frog (L. pipiens), and the spring peeper (Pseudacris crucifer) from multiple months of the year were sampled to determine if skin thickness increased in the autumn or winter months. Seasonal skin thickening was only detected in L. catesbeianus, and skin from autumn and winter was significantly thicker than from earlier in the year. This pattern was also detectable in museum specimens collected 80 years ago, although the signal was damped, possibly due to preservation. Using a dataset of 10 species and published data, a general pattern was uncovered whereby the dorsal skin is the thickest region and the ventral thigh region is the thinnest. However, this pattern is not always true for every individual of every species (L. pipiens and P. crucifer) and in some species the dorsal skin is thinnest (Bokermannohyla alvarengai and Litoria infrafrenata). The same dataset found that skin thickness is significantly related to body size, as was found in the chapter on Litoria infrafrenata. Summer specimens of Lithobates catesbeianus were outliers below the interspecific regression line and winter specimens fell within the range of variation of other species, hinting that seasonal skin thickening could be renamed seasonal skin thinning in this species. Finally, a link between ecology and skin thickness was tested using the 10 species from previous analyses and data from the literature. At a phylogenetially broad scale, body size explained a greater amount of the variation in environmental parameters than skin thickness. At smaller taxonomic scales, skin thickness appears more closely linked with ecology. It is concluded that amphibians generally follow an allometric trend for skin thickness and when faced with suboptimal conditions over long periods of time, evolve integumentary structures like iridiophores to compensate for any physiological disadvantage of an ‘ideal’ skin thickness. In the interim, however, skin thickness may change, thus sacrificing e.g. mechanical support.

The early Pliocene Gray Fossil Site (GFS) is a biodiverse site with a unique faunal assemblage that represents one of few sites of its age in eastern North America. A community structure analysis of the mammals at GFS was done to characterize species and better understand the paleoenvironment. Data and was gathered from twenty modern communities and five late Neogene sites to compare with GFS. Species from these 26 sites were categorized by body size, locomotor mode, cheek tooth crown height, and diet to characterize niches occupied. Descriptive statistics contrasted proportions of species within categories across communities. Discriminant function analyses (DFA) determined characteristics that best differentiate communities and classified fossil site habitat types. DFA results indicate that the GFS paleoenvironment was a habitat most similar to modern temperate forest regions in the eastern U.S. and China. Characteristics of GFS are dissimilar from other late Neogene sites examined in this study.

The limb skeleton of tapirs (Perissodactyla: Tapirus spp.) was traditionally thought to exhibit morphological variation only as a result of changes in body size. Here, we test whether forelimb variation exhibited by Tapirus is solely an artefact of size fluctuations through the tapir fossil record or whether it is influenced by habitat differences. We investigated the forelimb osteology of 12 species of Tapirus using three-dimensional geometric morphometrics on laser surface scans. Aligned shape coordinates were regressed against intrinsic bone size to account for allometry. Taxa of equivalent body mass exhibited significant differences in size-corrected bone shape. Stable carbon isotope values were averaged per species as a proxy for habitat density. Multivariate regressions of the humerus, pisiform, cuneiform, unciform, third and fourth metacarpals revealed no significant influence of size on shape. The lateral carpals (pisiform, cuneiform, unciform) demonstrated variation across the habitat density gradient. Observed variation is likely driven by species in the extinct subgenus Helicotapirus tapirs, which inhabited drier, more open woodland than modern taxa. We conclude that tapir forelimb variation is not exclusively an artefact of body size, with lateral wrist bones displaying notable differences across a habitat density gradient, beyond that resulting from size and phylogenetic effects.

Alligatorines are a diverse clade of crocodylians whose history spans the entire Cenozoic. They are suited to answer a variety of questions with far‐reaching impacts due to their physiology and preservation potential, and have been the subject of several phylogenetic, biogeographic, and diversity analyses. However, prior phylogenetic analyses had poor resolution and several putative alligatorines have never been included, while other analyses would be more informative and accurate if viewed through the context of evolutionary history. Here, I analyze the phylogenetics, taxonomy, biogeography, ecomorphology, and diversity dynamics of alligatorines. An almost fully resolved phylogenetic hypothesis returns two major clades within Alligatorinae and includes several putative alligatorines not previously analyzed. The clade originated in North America and dispersed to Europe and Asia three to five times via at least three different corridors at high latitudes when climate—and potentially salinity—were favorable, likely including the recently discovered subaerial Lomonosov Ridge. The modern American alligator is a dietary generalist, but evolved from a durophagous specialist, contrary to the intuitive reasoning of the “Law of the Unspecialized”. It was able to do so by entering the generalist niche vacated by basal crocodyloids following their extirpation from mid‐latitude North America. Alligatorine diversity only weakly tracks climate change and does not track the rock record excepting swampy environments. Alligatorine diversity correlates with climate change. Climate change correlates with rocks, though in a more complicated pattern. Some diversity metrics correlate with some aspects of the rock record, but predominantly do not. There is more support for the common‐cause hypothesis than for rock record bias driving apparent alligatorine diversity. Overall, alligator evolution exhibits a pattern of being more diverse taxonomically and morphologically when the climate is warmer, and dispersing during the warmest and wettest of those times.

Ever since Darwin claimed that expanding savannas were the driving force behind humanity's divergence from other apes, our understanding of human evolution has been inextricably linked to the environmental context in which our ancestors evolved. This dissertation explores various aspects of the use of one method of paleoenvironmental reconstruction -- bovid ecomorphology -- and provides new data on paleoenvironmental conditions in the Omo Shungura Formation (Plio-Pleistocene, Ethiopia). Chapter 2 uses phylogenetic simulations to explore the performance of Discriminant Function Analysis (DFA) on simulated ecomorphological data containing phylogenetic signal. DFA is shown to "over-perform" in situations in which predicted and predictor variables both contain phylogenetic signal. Phylogenetic Generalized Least Squares (PGLS) is shown to be a very useful technique for explicitly testing functional hypotheses in ecomorphology while controlling for phylogenetic signal and body size. Chapter 3 presents a functional analysis of the bovid astragalus, which is one of the most commonly preserved bones in the fossil record. Several functional hypotheses linking habitat-specific locomotor performance with the morphology of the astragalus are tested using PGLS. Strong support is found for three of these hypotheses. Thus, the astragalus is shown to be a useful ecomorphological predictor element, a point that is confirmed by the DFA analyses in Chapter 4. Chapter 5 provides new paleoenvironmental data on the Omo Shungura Formation based on habitat reconstructions from astragalar ecomorphology in addition to dietary reconstructions based on dental mesowear. Astragalar data point to a major environmental shift beginning ~2.58 Ma, which is later in time compared with some prior habitat reconstructions using different methods. Furthermore, astragalar data show environmental fluctuations of similar magnitude later in the sequence. Mesowear data on the Shungura Tragelaphini do not offer evidence for any significant grazing adaptation, in spite of relatively high carbon isotope signatures reported based on studies of tooth enamel. These data raise questions regarding the diet of fossil Tragalephini. / text

Functional morphologists have extensively used measurements of performance to investigate the relationship among form, function and ecology through ontogeny. Among different measurements of performance bite force play a crucial role influencing fitness. Although, bite force has been thoroughly investigated among vertebrates, the majority of the studies on fishes have been concentrated only in small species. Consequently, this is the first study that compares the bite force performance in two large marine predators, the great barracuda (Sphyraena barracuda) and bull shark (Carcharhinus leucas). Values of posterior bite force in S. barracuda varied from 3 - 258 N for an ontogenetic series of 27 individuals (23 - 130 cm, TL). Bite force as well as the majority of the biomechanical variables that contribute to it scaled with isometry in S. barracuda. Values of posterior bite force in C. leucas varied from 170 - 5,914 N for and ontogenetic series of 16 individuals (73 - 285 cm, TL). Bite force at the most anterior bite point scaled with positive allometry as well as the majority of the subdivisions of the adductive musculature that greatly contribute to bite force. Bite force performance in this two species showed strong differences, where S. barracuda has one of the lowest relative values of bite force among fishes and C. leucas has one of the largest ones. Additionally, the scaling patterns for bite force and most of the biomechanical variables investigated in this study differed among these two species. These results suggest that predatory success may be acquired by different strategies, and that the same ecological role in a marine ecosystem may be reached by having different bite force performance.

Pocket gophers (family Geomyidae) are the dominant burrowing rodents in North America today. Their fossil record is also incredibly rich; in particular, entoptychine gophers, a diverse extinct subfamily of the Geomyidae, are known from countless teeth and jaws from Oligocene and Miocene-aged deposits of the western United States and Mexico. Their postcranial remains, however, are much rarer and little studied. Yet, they offer the opportunity to investigate the locomotion of fossil gophers, shed light on the evolution of fossoriality, and enable ecomorphological comparisons with contemporaneous rodents. We present herein a quantitative study of the cranial and postcranial remains of eight different species of entoptychine gophers as well as many contemporary rodent species. We find a range of burrowing capabilities within Entoptychinae, including semifossorial scratch-digging animals and fossorial taxa with cranial adaptations to burrowing. Our results suggest the repeated evolution of chisel-tooth digging across genera. Comparisons between entoptychine gophers and contemporaneous rodent taxa show little ecomorphological overlap and suggest that the succession of burrowing rodent taxa on the landscape may have had more to do with habitat partitioning than competition.

The morphology of mammoth upper third permanent molars (M3) is used to address regional- and continental-scale patterns in the structure of mammoth populations. Recent refinements to the understanding of Mammuthus phylogenetic diversity south of the Laurentide ice show extensive overlap between regional populations. We assess the underlying geographic structure in Mammuthus tooth morphology in light of these new genetic data. Comparison of regional trends in dental morphology show a single, morphologically variable, population of Mammuthus was present in North America during the Wisconsin glaciation. Within this population, there are no significant differences in degree of hypsodonty or molar shape however, there is a geographic pattern of lower enamel:dentin ratios in Mammuthus from the Channel Islands, West Coast, and Southwest/Mexico as measured by the number of molar lamellae and the standardized thickness of lamellae. These results contrast with historical perspectives of Mammuthus population structure suggesting at least four species of North American mammoths but are consistent with recent phylogeographic analyses of mitochondrial ancient DNA.

No description available.