Browsing by Subject "Fossils"
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Item 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 Conceptualizing vertebrate faunal dynamics : new perspectives from the Triassic and Eocene of Western North America(2013-05) Stocker, Michelle Renae; Bell, Christopher J., 1966-Conceptualizations of actual biological patterns as preserved in the fossil record must accommodate the results of biotic and abiotic drivers of faunal dynamics. However, those conceptualizations also may reflect cognitive biases resulting from foundational philosophical stances. Whether fossils are conceptualized as the remains of biological entities or as geological objects will affect both taxonomic identifications and secondary inferences derived from those identifications. In addition, operational research bias centered on relativistic views of ‘importance’ of particular components (i.e., taxonomic or skeletal region) of the assemblage results in preferential documentation of some taxa and marginalization of others. I explored the consequences of those specific cognitive and operational biases through examination of Triassic and Eocene faunal assemblages in western North America. For the Triassic I focused on taxonomic and systematic treatments of Paleorhinus, a group of phytosaurs important for the establishment of biochronologic correlations. Specimen-level reexamination of Paleorhinus supported a restricted usage of Paleorhinus as a clade, dissolved a biochronologic connection between terrestrial and marine deposits, and indicated a prior compression of the early part of the Late Triassic as a result of previous conceptualizations of species. I reexamined the Otis Chalk tetrapod assemblage in light of new specimens and modern phylogenetic frameworks. My examination supported a restricted usage of the Otischalkian for biochronologic correlation of the Late Triassic, and emphasized the importance of apomorphic character-based specimen examinations in conjunction with detailed lithostratigraphy prior to the development of biochronologic schema. For the Eocene I focused on undocumented terrestrial reptiles from the late Uintan fauna of West Texas. Specifically I discovered new taxa and new geographic occurrences of amphisbaenians and caimanine crocodylians. The amphisbaenians represent the southernmost record of the clade in the North American Paleogene, and, when combined with other amphisbaenian records, document that the clade responded to late Paleogene climatic changes in ways different from the inferred mammalian response. The new taxon of caimanine crocodylian represents a new geographic and temporal record of that clade. That new record indicates that the biogeographic range of extant caimans represents a climate-driven restriction from a formerly more expansive range, and suggests that the previous geographic and temporal gap in paleodistribution data is related to sampling biases and is not a solely a biological phenomenon. These data indicate that reliable characterization of vertebrate faunal dynamics requires open acknowledgment and appropriate documentation of cognitive and operational biases that affect interpretations of paleontological data.Item Effects of taxonomic and locality inaccuracies on biostratigraphy and biochronology of the Hueso and Tapiado formations in the Vallecito Creek-Fish Creek section, Anza-Borrego Desert, California(2008-12) Murray, Lyndon Keith; Bell, Christopher J., 1966-The fossiliferous sediments of the Hueso and Tapiado formations exposed in the Vallecito Creek-Fish Creek section (VCFC) of the Anza-Borrego Desert (ABD) span the boundary between Blancan and Irvingtonian North American Land Mammal 'Ages.' Historically, the determination of the Blancan-Irvingtonian (B-I) boundary in the VCFC proved problematic. A new study to determine the B-I boundary in the VCFC revealed data inaccuracies in both published works and curatorial records of the mammal and other vertebrate fossils from the ABD. Most individual inaccuracies were minor, but an accumulation of over 50 years of multiple inaccuracies had significant effects on local and regional biostratigraphic and biochronologic correlations. A detailed investigation of the inaccurate data resulted in recognition of 17 types of error, with at least five sources. The two most prominent sources of error are those derived from publication and curation protocols. Examination of over 150 publications and in-house faunal lists produced over 830 taxonomic names and format variants, for 110 mammalian taxa identified from the ABD and VCFC. Approximately 50% of the taxonomic identifications were previously published without voucher catalogue numbers or fossil descriptions. A critical review of the taxonomic assignments resulted in an updated faunal list of ABD terrestrial Mammalia, including 110 taxonomic names, 66 unqualified genera, and 46 unqualified species. A supplemental list of 'retired' taxa includes 178 previously published or listed taxonomic names and format variants. The 4.5 km sequence of originally superposed sediments within VCFC is now tilted at 23 degrees and exposed in plan view. This exposure was captured in both aerial photos and satellite imagery. GIS layers of the Geomagnetic Polarity Time Scale and individual collecting localities are readily superposed onto the stratigraphic images. When united with the faunal database, GIS maps of biostratigraphic data facilitate detection and correction of data errors. Resulting corrected maps show highest and lowest stratigraphic occurrences of taxa, as well as geographic clustering of taxonomic groups, outlining possible paleohabitats. As a result of data improvement and GIS display, the local B-I boundary currently is best estimated by the presence of Ovibovini at >1.42 Ma.Item New records of early Jurassic gladius-bearing coleoids (Prototeuthidina and Loligosepiina) from Alberta, Canada(2016-05) Marroquin, Selva Mariana; Martindale, Rowan C.; Bell, Christopher J; Sprinkle, James T; Molineux, Ann MThe Ya Ha Tinda Lagerstätte from Alberta, Canada, preserves organic-rich black shales that capture the carbon isotope excursion (CIE) characteristic of the Toarcian Oceanic Anoxic Event (183 Ma). Excavations at Ya Ha Tinda uncovered fifteen Vampyropoda fossils from Pliensbachian and Toarcian strata. Vampyropoda are a group of cephalopods with eight arms and an internalized chitinous shell called a gladius. Ya Ha Tinda represents the largest record of Vampyropoda gladii found outside of Europe for the Early Jurassic, and provides the unique opportunity to place Vampyropoda in a chemostratigraphic context. The goals of this thesis were threefold: (1) to taxonomically identify the Vampyropoda found at Ya Ha Tinda, including two specimens that were collected by Russell Hall from the same formation in the 1980s, (2) to compare the distribution and paleoecology of Vampyropoda to coeval European Lagerstätten, and (3) to conduct a detailed analysis of how Vampyropoda taxa were influenced by the Toarcian Oceanic Anoxic Event. In total, only fourteen specimens have sufficient morphological details preserved for taxonomic descriptions. Twelve specimens are identified to the genus level; six Paraplesioteuthis cf. sagittata, three Loligosepia cf. aalensis, one Geopeltis cf. simplex, one Parabelopeltis cf. flexuosa, and one Jeletzkyteuthis sp. The remaining two specimens belong to the suborder Loligosepiina, one to the family Geopeltididae. With the exception of Paraplesioteuthis, this is the first time all of these taxa have been found outside of Europe. The discovery of L. cf. aalensis within Pliensbachian strata pushes back the earliest occurrences of these taxa from the Early Toarcian to the Late Pliensbachian. Vampyropoda discovered at Ya Ha Tinda are nearly identical to those found in German deposits of the coeval Posidonia Shale, but, unlike European Lagerstätten, the fauna from Alberta has a relatively even proportion of Prototeuthidina and Loligosepiina. There are no taxa found within the CIE interval. The absence of taxa from this interval may be a result of taphonomy, sampling bias, or water chemistry. My results highlight several challenges associated with Vampyropoda taxonomy and provide paleoecological data of Early Jurassic specimens that are vital for understanding the taphonomic controls influencing the fragmentary Vampyropoda fossil record.Item Systematic paleontological investigation of the metatherian fauna from the Paleogene Uzunçarşıdere Formation, central Turkey(2008-12) Maga, Ali Murat, 1973-; Bell, Christopher J., 1966-The name Metatheria refers to the clade that contains the extant marsupials and also all extinct mammals that are more closely related to extant marsupials than to the placental mammals. Metatherians first appear in the fossil record of Asia during the Early Cretaceous, with younger records in North America (Late Cretaceous), South America (the latest Cretaceous or earliest Paleocene), and finally Australia via Antarctica (by the Eocene). The Cenozoic fossil record of metatherians in the Old World is rather poor. Except for Europe, there are only a handful of metatherian taxa known from Afro-Arabia and Asia, almost all of which are documented only by isolated teeth or partial jaws. Fieldwork at Uzunçarşı, a fossil site in central Turkey, yielded at least three different metatherian taxa, one of which (Anatoliadelphys) is exceptionally preserved and nearly complete. In this study I demonstrate that Anatoliadelphys occupies a more derived position on the metatherian tree than the well-known South American metatherians such as Pucadelphys. My functional morphological investigations indicate that Anatoliadelphys and the South American taxa Pucadelphys and Mayulestes are different from the extant didelphid marsupials of South America in their skeletal adaptations for locomotion. Anatoliadelphys was most likely terrestrial.Item Trends in evolutionary morphology : a case study in the relationships of angel sharks and batoid fishes(2010-05) Claeson, Kerin Michele; Bell, Christopher J., 1966-; Rowe, Timothy B.; Hendrickson, Dean; Sprinkle, James; McEachran, John D.Chondrichthyans are cartilaginous fishes that include the extant chimaeras, sharks, and batoids, and their extinct relatives. In this dissertation, I examined the growth, development, and relationships of extinct and extant chondrichthyans. I reexamined the skeleton of fossil and fetal specimens of the angel sharks (Squatiniformes) and reanalyzed the current morphologically based hypothesis of chondrichthyan evolution, which conflicts with the current molecular based hypothesis. I did this by including extinct taxa and new characters based on dentition, and the ethmoid, occipital, pectoral, and vertebral skeleton. My results supported the pre-existing morphological hypothesis that angel sharks, saw sharks, and batoids form a clade. However, some of my new characters, particularly those based on the vertebral morphology, indicate that fetal and juvenile angel sharks do not share as many apomorphies with batoids as previously hypothesized from the examination of adults. I also examine the relationships of major groups within batoids, beginning with the construction of a hypothesis of the evolutionary history of electric rays (Torpediniformes). My results are consistent with previous rank-based classifications. However, they deviate from previous classifications depending on the criteria used to generate the hypothesis and on which taxon, or combination of taxa, were used to root the ingroup phylogeny. Because pectoral and vertebral morphology are so critical to morphological hypotheses, I also examined the growth and development of the synarcual cartilage in batoid fishes, with particular emphasis on the synarcual of skates (Rajiformes). My results demonstrate that calcification and chondrification do not proceed in the same order, temporally and spatially. Finally, I redescribe the extinct batoid †Cyclobatis, known only from the Cretaceous, and evaluate its phylogenetic position. My results indicate that †Cyclobatis, the oldest known rajid, is also the sister taxon to a clade of all known extant members of Rajidae. Furthermore, the inclusion of new characters, mainly derived from the synarcual, help to resolve the interrelationships of Rajidae.Item Two new archosaur reptiles from the late Triassic of Texas(Texas Tech University, 2002-08) Atanassov, Momchil NikolaevTwo new basal archosaurs, Pteromimus longicollis and Procoelosaurus brevicollis are described from the Tecovas Formation (late Camian) and the Cooper Canyon Formation (early Norian) of the Dockum Group of West Texas. Pteromimus is based on an incomplete skull and associated and isolated skull and vertebral elements. The skull is high, with narrow snout, large orbit and naris, pneumatized maxilla and premaxilla, large inflated frontal, short parietal, plate-like supraoccipital, and reduced post-temporal openings. The dentition is thecodont and consists of conical teeth with fluted apices. The premaxillary teeth are long and slightly recurved, and the maxillary teeth are short and more laterally compressed. The vertebrae of both Pteromimus and Procoelos aurus £ire with procoelous and hollow centra, with large cavities for the interspinal ligament, well-developed epipophyses, and long and low neural arches carrying long neural processes v«th spine tables. Pteromimus is distinguished by low neural processes with weakly developed spine tables and ornamentation, while Procoelosaurus is characterized by higher neural processes that expand into wide spine tables with distinctive sculpturing. The cervical vertebrae of Pteromimus are elongate, dorsoventrally compressed, and bear unusual rib articulations consisting of a large posterior depression and a small anterior process. Procoelosaurus is represented by an association of vertebrae, pelvis, hindlimb and skull elements, and by a large number of isolated vertebrae. The maxilla and dentary of Procoelosaurus bear numerous teeth with thecodont implantation and crowns that are recurved, laterally compressed, and serrated. Procoelosaurus has at least three sacral vertebrae, large plate-like ischium, and ilium with a low blade, reduced preacetabular process, and a long, tapering postacetabular process. The femur appears similar to those of pterosaurs with anteriorly bowed shaft, well developed condyles, and an intumed head. The ankle and foot of Procoelosaurus are similar to those of early pterosaurs with an advanced mesotarsal tarsus, hooked fifth metatarsal, and closely appressed metatarsals I-IV subequal in length and indicating a plantigrade pes. A phylogenetic analysis of Archosauromorpha indicates that the two new reptiles and pterosaurs are omithodiran archosaurs and form a monophyletic clade that is the sister-group to Scleromochlus + Dinosauromorpha. Pteromimus is the sistergroup of pterosaurs, and Procoelosaurus is the sister-group to the clade Pteromimus + Pterosauria.Item Variation within the bony labyrinth of mammals(2009-12) Ekdale, Eric Gregory; Rowe, Timothy, 1953-The morphological diversity of the external and internal surfaces of the petrosal bone, which contains the structures of the inner ear, across a broad range of therian mammals is documented, and patterns of variation across taxa are identified. One pattern of variation is the result of ontogenetic changes in the ear region, as described for the external surface morphology of a sample of isolated petrosal bones referred to Proboscidea from Pleistocene deposits in central Texas. The morphology of the aquaeductus Fallopii for passage of the greater petrosal branch of the facial nerve supports an ontogenetic explanation for some variation within the proboscidean sample, and a sequence of ossification surrounding the aquaeductus Fallopii is hypothesized. Further ontogenetic patterns are investigated using digital endocasts of the bony labyrinth (preserved on the internal surfaces of the petrosal) constructed from CT data across a growth series of the opossum Monodelphis domestica. Strong correlation between skull length and age is found, but from 27 days after birth onward, there is no correlation with age among most dimensions of the inner ear. Adult dimensions of several of the inner ear structures are achieved before the inner ear is functional in M. domestica. Morphological variation within the inner ear of several eutherian mammals from the Cretaceous of Asia, including zhelestids from the Bissekty Formation of Uzbekistan, is described. The variation within the fossil sample is compared to that observed within extant species of placental mammals, and it is determined that the amount of variation within the Bissekty zhelestid population is within the range of that measured for extant species. Additional evolutionary and physiological patterns preserved within the walls of the bony labyrinth are identified through a high level anatomical comparison of the inner ear cavities across Placentalia as a whole. In particular, features of the inner ear support monophyly of Cetacea, Carnivora, Primatomorpha, and caviomorph Rodentia. The volumetric percentage of the vestibular apparatus (vestibule plus semicircular canals) of aquatic mammals is smaller than that calculated for terrestrial relatives of comparable body size. Thus, aspects of the bony labyrinth are both phylogenetically and physiologically informative.