Browsing by Subject "Paleoecology"
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Item A study of two isolated Cambrian stromatolitic outcrops, Mason and McCulloch counties, Texas(Texas Tech University, 1987-05) Portnoy, Michael BenjaminNot availableItem Alternative approaches to the identification and reconstruction of paleoecology of Quaternary mammals(2012-12) George, Christian Owens; Bell, Christopher J., 1966-; Czaplewski, Nicholas J; Leibold, Matthew A; Rowe, Timothy; Sprinkle, James TSince the 19th century the remains of Quaternary mammals were an important source of data for reconstructing past environmental conditions. I tested two basic assumptions that underlie Quaternary vertebrate paleoecology. The first assumption is that fossils mammals can be identified reliably to species. The second assumption is that correlations established between extant mammals and environmental parameters can be used to interpret reliably the paleoenvironment from the latest Pleistocene. Incorrect specimen identifications could lead to errors in paleoecologic interpretations. I explicitly tested an alternative to the traditional approach to identification by identifying fossil shrews based on apomorphies. My results indicated that some traditional characters are useful for identification, but only complete specimens with a combination of characters can be identified to species. This indicates that previous authors who identified shrews to species did not compare them to the full diversity of species. I tested the reliability of cenograms and species-richness models as approaches for the reconstruction of environmental conditions in the past. I used faunal data from Hall’s Cave, Kerr County, Texas to construct cenograms and species-richness models and compared the results to independent paleoclimate proxies. Neither species-richness models nor cenograms agree with paleoenvironmental reconstructions based on proxy data from the Late Pleistocene and Holocene. Cenograms and species-richness models are unreliable and fraught with problems, and both approaches should be abandoned as tools for paleoecological reconstruction. To test for potential geographic bias in the identification of Quaternary fossils I developed a GIS (geographic information systems) database of Quaternary paleontological sites within Texas. I was able to show that the identification of species of fossil soricids, heteromyids, Odocoileus, and Spilogale was influenced by geography. Those fossils should be treated as generic identifications until they are re-evaluated against the full diversity of species. Utilizing GIS I also developed a method of paleoecological analysis. My analysis showed that the environmental conditions found today in Texas might not be limiting the current range of shrews. Based on the known geographic range of shrew fossils, other ecological factors besides environmental conditions are shaping the current distribution of shrews.Item An applied paleoecology case study: Bahia Grande, Texas prior to construction of the Brownsville Ship Channel(Texas A&M University, 2006-08-16) Lichlyter, Stephen AlvahBahia Grande is a large lagoon located within Laguna Atascosa National Wildlife Refuge in Cameron County, Texas. When the Brownsville Ship Channel was built along the southern end of the lagoon in 1936, Bahia Grande was cut off from the marine water of Laguna Madre. Since that time, Bahia Grande has been primarily dry with only ephemeral fresh water coming from heavy rainfall events, resulting in a severe decline in biological productivity. A restoration project led by the U.S. Fish and Wildlife Service has proposed to cut new channels between Bahia Grande and the Ship Channel to restore the connection with Laguna Madre. This is a large-scale project with major implications for the water quality, surrounding ecology, and associated biota in the region. Unfortunately, because very little is known about Bahia Grande prior to isolation, it is difficult to predict whether the results of the restoration will be comparable to the pre-Ship Channel environment. Paleoecological data provide the best opportunity to understand what Bahia Grande was like in the past. This study uses statistical analyses of the molluscan death assemblages from Bahia Grande to gain a better understanding of the environmental conditions in the lagoon before it was isolated. The first question addressed is how does Bahia Grande relate to other water bodies on the Texas coast? This may provide a modern analog to the past conditions in Bahia Grande. The second question inquires whether there are any local patterns or variations within Bahia Grande and several smaller surrounding lagoons. These results provide an important baseline for comparison with the restored lagoon. The results of this investigation show that, in a regional context, Bahia Grande was most similar to Alazan Bay and Baffin Bay, which are mostly enclosed shallow bays with high salinities due to the arid climate and limited freshwater inflow. Within Bahia Grande, there are several distinct molluscan assemblages. Salinity and water coverage are the most likely environmental factors responsible for the differences within Bahia Grande. Additionally, data from surrounding lagoons strongly indicate that some connections with Bahia Grande existed in the past.Item The paleoenvironments of early hominins in the Omo Shungura Formation (Plio-Pleistocene, Ethiopia) : synthesizing multiple lines of evidence using phylogenetic ecomorphology(2014-05) Barr, William Andrew, active 21st century; Reed, Denné N.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.Item Pollen from Laguna Verde, Blue Creek, Belize: Implications for Paleoecology, Paleoethnobotany, Agriculture, and Human Settlement(2010-10-12) Morse, MckenzieThis dissertation is a palynological examination of the Mayan archaeological site at Blue Creek, northwestern Belize. This study uncovers more than 4,500 years of environmental and agricultural history of the region, which can be related to human incursion, habitation and plant use, abandonment, and reoccupation of the region. After an historical and ecological overview of the study site, there follows an explanation of procedures for collecting, sampling, processing, identifying, and counting the fossil pollen from the area. Evidence from archaeology, paleoecology, and physical anthropology is used to construct a model for the first entry of humans into the Maya area. Examinations are made of Archaic Period paleoecology and the cultural developments that set the stage for the advancement of Maya culture. Next, the physical environment of Blue Creek is explored, and its stability is assessed. This information leads to an assessment of the possibility of drought or soil degradation during the height of Mayan civilization, and contributes to the current understanding of the Maya Collapse at Blue Creek. Mayan agricultural methodologies are explained, and the changes to traditional production systems that resulted from European colonization are described. A model of agricultural development is proposed. The plant taxa identified in the Laguna Verde pollen core are listed and described. Finally, the Laguna Verde pollen core is interpreted in terms of the vegetation associations and environmental conditions represented by each stratum. This dissertation is a palynological examination of the Mayan archaeological site at Blue Creek, northwestern Belize. This study uncovers more than 4,500 years of environmental and agricultural history of the region, which can be related to human incursion, habitation and plant use, abandonment, and reoccupation of the region. After an historical and ecological overview of the study site, there follows an explanation of procedures for collecting, sampling, processing, identifying, and counting the fossil pollen from the area. Evidence from archaeology, paleoecology, and physical anthropology is used to construct a model for the first entry of humans into the Maya area. Examinations are made of Archaic Period paleoecology and the cultural developments that set the stage for the advancement of Maya culture. Next, the physical environment of Blue Creek is explored, and its stability is assessed. This information leads to an assessment of the possibility of drought or soil degradation during the height of Mayan civilization, and contributes to the current understanding of the Maya Collapse at Blue Creek. Mayan agricultural methodologies are explained, and the changes to traditional production systems that resulted from European colonization are described. A model of agricultural development is proposed. The plant taxa identified in the Laguna Verde pollen core are listed and described. Finally, the Laguna Verde pollen core is interpreted in terms of the vegetation associations and environmental conditions represented by each stratum.