• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 117
  • 74
  • 35
  • 21
  • 20
  • 4
  • 3
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 363
  • 181
  • 71
  • 49
  • 48
  • 40
  • 34
  • 32
  • 27
  • 27
  • 26
  • 24
  • 24
  • 23
  • 23
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
71

Evolutionary patterns in the reef coral Siderastrea during the Mio-Pliocene of the Dominican Republic

Beck, Brian Robert 01 January 2005 (has links)
No description available.
72

A geometric morphometric analysis of contemporary Hispanic populations from Mexico and Colombia

Calle, Sergio 30 January 2020 (has links)
In contexts such as natural disasters, humanitarian efforts, and other forensic investigations, the timely and accurate development of the biological profile (sex, age, ancestry, and stature of skeletonized remains) is vital to the identification of decedents. At present, the term “Hispanic” is a socio-linguistic classifier that includes all persons of South or Central American, Mexican, Cuban, Puerto Rican, or other Latino and Spanish-speaking persons into a single category; the term is also the current designator used by forensic anthropologists—in ancestry estimation—to identify anyone from a Latin American country. From a biological standpoint, the term is ineffective in describing these individuals because the human biological variation within and among different Hispanic populations cannot be encompassed by a single category. With regards to the development of the biological profile, ancestry estimations for these individuals are tenuous at best. This is due to the poor nature of the single reference sample used to create the current methods in ancestry and sex estimation—a common trend in forensic anthropology. The untested assumption that all Hispanic individuals are skeletally homogenous results in haphazard identifications and hinders effective forensic investigation. The primary objective of this research is to examine geometric morphometric variability in 547 documented individuals from three contemporaneous Latin American groups represented by Colombian, Mexican, and Migrant (U.S./Mexico border crossers) samples in order to ascertain whether it is possible to distinguish specific Hispanic populations. Using geometric morphometric (GM) analyses, the effects of shape-related variation independent of size can be implemented to isolate where on the cranium differences between groups are expressed. The results suggest that GM-derived population-specific criteria for Hispanic individuals possess the discriminatory power that is necessary towards improving the underdeveloped methods of identification for diverse Hispanic individuals living in the U.S. and abroad. Canonical variate analyses of the three samples separates the groups distinctly along both axes (CV1 and CV2). The morphological differences are predominantly seen in cranial height and sagittal vault shape, with Colombians having taller cranial vaults than the Mexican samples. The final results of this study demonstrate the utility that GM approaches have in forensic anthropology with respect to ancestry estimation and can be used to update various techniques required to develop the biological profile. Without constantly updating, refining, and re-validating the techniques, forensic anthropologists fail to provide the caliber of service required to approach the various forensic contexts.
73

Intervertebral Variation of North American Pit Vipers (Squamata, Viperidae) Using Geometric Morphometrics

Jessee, Lance D., Gause, Austin, Schubert, Blaine W. 12 April 2019 (has links)
Within Pleistocene cave deposits, snake fossils tend to be relatively common and generally occur as isolated vertebrae. However, the specific, and sometimes generic, identification of isolated snake vertebrae is often hindered by the significant amount of intra- and interspecific variation along the precloacal vertebral column, a subject that has largely been neglected in many fossil snake identifications. Identifications are typically based on the vertebrae of disarticulated modern specimens with preference given to mid-trunk vertebrae. This study utilizes 2-D geometric morphometrics to determine the extent of intervertebral variation along the precloacal vertebral column of North American pit vipers of the genera Crotalus (rattlesnakes) and Agkistrodon (copperheads and moccasins), two closely related genera geographically sympatric in northeast Tennessee and much of the eastern United States with similar vertebral morphologies. The focus of this study is to determine the need for identifying the morphological regionalization of the precloacal vertebral column and determining the regional position of isolated vertebra prior to identification. Using one individual from each genus, every third vertebra was chosen and analyzed in anterior view using geometric morphometrics and relative warp analyses. A discriminant function analysis was then performed to distinguish between the two genera. Viperid fossils from Hickory Tree Cave in northeast Tennessee underwent the same geometric morphometric and discriminant function analyses as a means of identification. It is expected that the relative warp analyses will show some morphological regionalization of the precloacal vertebral column, but may prove to not be significant enough for use in the identification of isolated vertebrae. In that case, comparison to mid-trunk vertebrae for identification may prove accurate. This study also shows the need for more modern skeletal specimens in herpetological collections and the need for preserving the vertebral order of those specimens.
74

Genetic and Morphometric Analysis of a Unique Population of Pondmussel (Ligumia) and its Implications for Other Species in Lampsilini (Family Unionidae)

Peters, Joshua C 01 December 2019 (has links)
Freshwater burrowing mussels (unionids) play a vital role in freshwater ecosystems through nutrient cycling and promoting biodiversity. They have unique life histories directly related to aquatic vertebrates during an obligate parasitic larval stage, known as glochidia. Human interference has largely impacted mussel populations causing them to become the most endangered group of animals in North America. Genetic data has revealed taxonomic issues related to valve morphology, such as valve plasticity and cryptic speciation, that has caused identification issues in the field. Using both genetic and morphometric methods, I determined the phylogenetic placement of an isolated population of mussels within the tribe Lampsilini. I also investigated whether this population was a morph of a previously known Lampsilin species or if they were worthy of being treated as an evolutionarily significant unit (ESU) or an undescribed species. In addition, I expanded the known phylogeny of Lampsilin by including three species (Lampsilis fasciola, Lampsilis hydiana, Ligumia subrostrata) not included in previous phylogenies. Genetic analysis involved sequencing cytochrome c oxidase subunit 1 (COI) and 16s ribosomal RNA (rrnL) genes and producing maximum likelihood trees with bootstrap values for each gene individually and combined. Genetic results showed that an population from an isolated pond (named Junk Pond in this study) were closely related to members of the genus Ligumia (pondmussels), with Ligumia subrostrata being their closest relative. Morphologically, these Junk Pond mussels were noticeably different from other Ligumia species, so genetic and morphometric data was used to try and characterize this population of mussels from Junk Pond. The genetic distance between these two groups, measured using K2P distance method, were like the distances of other known sister species within Lampsilini. Morphometric analysis involved landmark and semi-landmark analyses to quantify the differences of the internal and external shapes of the shell, respectively, and determine differences that could be species defining characteristics. Landmark analysis results showed that Ligumia subrostrata and the Junk Pond mussels had similar internal valve structures though semi-landmark results showed differences among all groups including L. subrostrata and the Junk Pond mussels. I determined that this isolated population, due to its geographic isolation, genetic differences, variant shell morphology, and limited population size, should be treated as an ESU. The expanded Lampsilin tree showed a few differences involving Ligumia nasuta that did not support a previously published tree. Many other relationships within this phylogeny agreed with previously published works. The isolated population of the Junk Pond mussels are worthy of future research using more genetic data, such as COI, and morphometric work involving other Lampsilin members in order to conclude whether this group are worthy of being recognized as an undescribed species.
75

Investigation into the Paleobiology of Dasypus bellus Using Geometric Morphometrics and Variation of the Calcaneus

Jasinski, Steven E., Wallace, Steven C. 01 January 2014 (has links)
The extinct taxon Dasypus bellus has long been considered identical to the extant Dasypus novemcinctus osteologically when disregarding allometric differences. In this study, we undertake a preliminary investigation into this extinct taxon and an extant relative D. novemcinctus, by comparing the calcanea of these two dasypodids. Clear osteological differences are observed including a mediolaterally-reduced facet region, an anteriorly-shortened calcaneal head, a reduced peroneal process, and a curved and dorsoventrally-shortened calcaneal foot in D. bellus. Such characters are not allometric and likely correlate to distinct behavioral differences. Specifically, we suggest that D. novemcinctus maintains a more fossorial lifestyle, while the larger D. bellus was likely more terrestrial, with potentially little digging behavior. Such lifestyle differences could not only explain the osteological differences present, but also why fossils of D. bellus have been recovered farther north than the present range of D. novemcinctus. Fossils of Dasypus may need to be re-evaluated to determine how these two taxa relate temporally and geographically, which may have further implications regarding some past interpretations and provide new details on the behavior and potential relationships between these (and other) xenarthrans.
76

A Contribution to the Evolutionary History of Ethiopian Hipparionine Horses (Mammalia, Equidae): Morphometric Evidence From de Postcranial Skeleton

Bernor, Raymond L., Scott, Robert S., Haile-Selassie, Yohannes 01 March 2005 (has links) (PDF)
A morphometric analysis of third metapodials and first phalanges of Middle Awash and Hadar hipparions dating from the 6.0-3.0 Ma interval was conducted using two methods. Morphological comparisons using standard metrics were made using: 1) log10 ratio diagrams; 2) size independent variables developed with reference to scaling trends for hipparions in general. Results of these analyses suggest that hipparion diversity during this temporal interval was relatively low. A single dominant gracile lineage of Eurygnathohippus Van Hoepen, 1930, most plausibly derived from the Lothagam (Kenya) species Eurygnathohippus feibeli (Bernor & Harris, 2003), would appear to have persisted throughout this interval and is marked by increases in size with measured change in metapodial and phalangeal morphology. A rarer, more robust form is found in the Ethiopian sample at 4.0 Ma and is morphometrically similar to Eurygnathohippus turkanense Hooijer & Maglio, 1973 from late Miocene horizons of Lothagam. Another smaller form, of uncertain systematic status, appears likely late in the Kada Hadar sequence, c. 3.0 Ma.
77

Morphological variability in human maxillary molars / ヒト上顎臼歯形態における変異性

Morita, Wataru 24 March 2014 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18109号 / 理博第3987号 / 新制||理||1575(附属図書館) / 30967 / 京都大学大学院理学研究科生物科学専攻 / (主査)教授 中務 真人, 教授 山極 壽一, 教授 疋田 努 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM
78

Critical Growth Processes for the Midfacial Morphogenesis in the Early Prenatal Period / 中顔面形態形成における胎児期初期成長の重要性

Katsube, Motoki 25 March 2019 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第21650号 / 医博第4456号 / 新制||医||1034(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 大森 孝一, 教授 斎藤 通紀, 教授 戸口田 淳也 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM
79

Landscape Phenomics of the Human Face

Kirkland, Scott, 0000-0003-2172-4342 January 2021 (has links)
The study of human cranial morphology has a long and contentious history. This study is the first large scale analysis of ecoregion specific human cranial modularity and integration. It utilizes an analysis of morphometric craniofacial variation and ecoregion affinity to better understand the environmental contribution to biological shape. This study tested three hypotheses. First, that there was variation in craniofacial shape that was linked to an individual’s ecoregion. Second, that there were ecoregion specific patterns of cranial modularity. And third, that the patterns of cranial integration (or the level of covariation between any two modules) were also associated with an individual’s ecoregion, and that different environments would result in different patterns of modular dependence and independence. Three-dimensional scans of 298 human crania were collected from museums, representing four higher level ecoregions and 11 lower-level ecoregions. Each cranium was mapped and placed within two hierarchical ecoregions. By examining ecoregions, instead of individual climatic variables, this analysis gives a more complete picture of how the environment is influencing cranial variation. Modules, or relatively independent morphological regions of the crania, were identified and their level of integration was assessed for every ecoregion. Modular integration is an analysis of the relative strength of the covariation between any two modules, and previous research theorized that changes in integration reflected changes in modular independence during development (Bastir and Rosas, 2005; Hall, 2005; Raff, 1996). The variation in strength between modules, both intrapopulation and interpopulation, were assessed and various explanations were explored. This analysis found that each ecoregion exhibited significantly different craniofacial shape from one another. Patterns of integration were also variable by ecoregion, suggesting that the ecological shape variation observed was solidified early in development. This study also identified the presence of a nasal module in each ecoregion. Overall, the findings of this study demonstrate that human crania are variable by ecoregion and that environmental conditions have led to ecoregion specific patterns of cranial modular integration. / Anthropology
80

The effect of maternal melatonin supplementation during mid to late gestation on offspring muscle growth and development in swine

Dobbins, Thomas Warren 09 August 2022 (has links) (PDF)
Melatonin is a neuroendocrine hormone most often associated with circadian rhythms, but also has antioxidant and vasodilative properties. Through these properties, exogenous melatonin supplementation has been shown to increase both fetal and postnatal parameters in livestock species, however no research has been performed in swine. This project was split into a prenatal and postnatal study, wherein sows were supplemented from approximately gestational day 38 to 100 before undergoing a terminal hysterectomy for the prenatal portion, and from gestational day 60 to farrowing. Melatonin increased fetal morphometrics in a seasonal dependent manner, where fetuses from melatonin supplemented sows had increased measurements in the Spring replicate. Across the Spring and Fall replicates of the prenatal study, melatonin altered expression of circadian regulatory, metabolic, and myogenic genes within the longissimus dorsi. During the postnatal study, offspring from melatonin supplemented dams had increased body weight and altered circadian regulatory, metabolic, and myogenic gene expression.

Page generated in 0.0623 seconds