Browsing by Subject "Triassic"
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Item Anatomy and relationship of Shuvosaurus, a basal theropod from the Triassic of Texas(Texas Tech University, 2005-05) Lehane, James; Chatterjee, Sankar; Barrick, James E.; Lehman, ThomasShuvosaurus inexpectatus was initially discovered in 1993 and was determined to be either an ornithomimosaur or a basal theropod. Later research proposed that the Shuvosaurus skull belonged to the postcranial material of Chatterjeea, based on association and relative sizes, but no anatomical evidence was presented. Recent research reconfirmed that Shuvosaurus is a basal theropod based on cranial characters. A complete reconstruction of the skull was done to evaluate the proper phylogeny of Shuvosaurus. Individual elements of the skull show a strong resemblance to basal theropods including Syntarsus and Coelophysis. Cladistic analysis using the cranial anatomy confirms that Shuvosaurus fits firmly in the basal theropods adjacent to Syntarsus in the Coelophysoidea. An analysis of the skull and endocast of Shuvosaurus reveals a large secondary palate with a groove for a horny beak, a shortened snout, an enlarged orbit, an enlarged olfactory bulb, and an enlarged floccular fossa. The horny beak and shortened snout are similar to turtles and birds. Birds with this type of beak feed primarily on nuts. The enlarged orbit and olfactory bulb indicates it had exceptional smell and sight. The enlarged floccular fossa indicates a high level of activity associated with bipedalism.Item Anatomy and relationship of Shuvosaurus, a basal theropod from the Triassic of Texas(2005-05) Lehane, James; Chatterjee, Sankar; Barrick, James E.; Lehman, ThomasShuvosaurus inexpectatus was initially discovered in 1993 and was determined to be either an ornithomimosaur or a basal theropod. Later research proposed that the Shuvosaurus skull belonged to the postcranial material of Chatterjeea, based on association and relative sizes, but no anatomical evidence was presented. Recent research reconfirmed that Shuvosaurus is a basal theropod based on cranial characters. A complete reconstruction of the skull was done to evaluate the proper phylogeny of Shuvosaurus. Individual elements of the skull show a strong resemblance to basal theropods including Syntarsus and Coelophysis. Cladistic analysis using the cranial anatomy confirms that Shuvosaurus fits firmly in the basal theropods adjacent to Syntarsus in the Coelophysoidea. An analysis of the skull and endocast of Shuvosaurus reveals a large secondary palate with a groove for a horny beak, a shortened snout, an enlarged orbit, an enlarged olfactory bulb, and an enlarged floccular fossa. The horny beak and shortened snout are similar to turtles and birds. Birds with this type of beak feed primarily on nuts. The enlarged orbit and olfactory bulb indicates it had exceptional smell and sight. The enlarged floccular fossa indicates a high level of activity associated with bipedalism.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 Evaluating stable isotope proxies (δ¹³C, δ¹⁸O, and δ¹⁵N) for detecting photosymbiosis in fossil corals(2016-05) Tornabene, Chiara; Martindale, Rowan C.; Bell, Christopher J.; Breeker, Daniel O.; Shanahan, Timothy M.Photosymbiosis is a mutually beneficial relationship that many scleractinian corals have developed with dinoflagellates called zooxanthellae. Photosymbiosis is often considered the evolutionary innovation that allowed corals to become major reef-builders; nevertheless it is difficult to determine whether ancient reef-building corals harbored symbionts because zooxanthellae are not preserved in the fossil record. Two stable isotope measurements were previously proposed as proxies for ancient photosymbiosis: δ18O/δ13C and δ15N. Modern zooxanthellate (Z) and azooxanthellate (AZ) corals can be differentiated by skeletal δ18O and δ13C due to fractionation caused by zooxanthellae photosynthesis (Stanley and Swart, 1995) and by the δ15N of their skeletal organic matrix because nitrogen is influenced by trophic lifestyle (Muscatine et al., 2005). In this study, Modern, Holocene, Oligocene, and Triassic coral skeletons with varying morphologies (Z-like and AZ-like morphologies) were analyzed for δ18O/δ13C and δ15N to test whether these geochemical techniques are applicable to the fossil record. To avoid altered signals due to recrystallization, samples were visually tested for diagenetic alteration through petrography and scanning electron microscopy (SEM). The δ18O and δ13C data displayed enriched isotopic values for both C and O in fossil corals and higher variability in Triassic corals than previously reported suggesting that the proxy is not dependable when used on fossil corals. The δ15N analyses of fossil material failed to reproduce the significant Z vs. AZ offset originally identified by Muscatine et al. (2005). Although AZ-like specimens were specifically selected, all of the samples were collected from shallow-water platforms and it is possible that they were zooxanthellate despite their morphology. It is also possible that all corals shared the same nitrogen sources by living in the same environment thus leading to similar organic matrix δ15N values. Future research on this proxy should focus on understanding the influence of the nitrogen cycle on organic matrix δ15N and analyzing fossil deep-water corals to establish whether the δ15N of fossil coral organic matrix can serve as a reliable proxy for ancient photosymbiosis. The establishment of a successful proxy for photosymbiosis will allow scientists to define the evolutionary relationship between coral-zooxanthellae symbiosis and reef-building.Item A fluid inclusion and cathodoluminescence approach to reconstruct fracture growth in the Triassic-Jurassic La Boca Formation, Northeastern Mexico(2011-12) Kaylor, Autumn Leigh; Laubach, Stephen E. (Stephen Ernest), 1955-; Eichhubl, Peter; Catlos, Elizabeth; Ketcham, RichardOpening-mode fracture shapes are typically the result of brittle deformation and proportional growth in fracture height, length, and width. Based on the typical fracture shape, it is assumed that fracture tips are free to propagate in all directions. Some natural rock fractures have been shown to form as a result of slow non-elastic deformation processes. Such fractures may propagate to a finite length or height and accommodate further growth by aperture widening only. To determine the growth conditions of a fracture in the Triassic-Jurassic La Boca Formation of northeastern Mexico and to test fracture growth models, I combined fluid inclusion microthermometry and SEM-based cathodoluminescence cement texture analysis to determine the relative timing of fracture cement precipitation and related fracture opening for five samples collected along its trace. Fracture growth initiated at a minimum age of 70 Ma as two separate fractures with branching fracture tips that coalesced to a single continuous fracture under prograde burial conditions at a minimum age of 54 Ma. At this stage, fracture growth was accommodated by both propagation (i.e. increase in trace length) and by an increase in aperture during maximum burial and early exhumation. Samples collected at the fracture tips recorded temperatures reflecting fracture opening starting with maximum burial at a minimum age of 48 Ma at one tip and of 38 Ma at the other tip. Synkinematic fluid inclusions in crack-seal cement track continued fracture opening close to the fracture tips without a concurrent increase in trace length after 38 Ma until about 21 Ma. I attribute the observed change in fracture growth mechanism to a change in material response. The stage in aperture increase without propagation corresponds to an increase in elastic compliance or in non-elastic flow properties. Non-elastic flow can be attributed to solution-precipitation creep of the host rock. Dissolution of host quartz grains and subsequent quartz precipitation is consistent with the abundance of quartz fracture cement formed during exhumation. Cement textures from fractures in the La Boca Formation mimic those found in subsurface core, which allows application of the results to a variety of geologic environments.Item Preparation, casting, and exhibition of Texas aetosaur, Desmatosuchus(Texas Tech University, 2000-05) Herzog, NikoAetosaurs (Family Stagonolepididae) are an extinct group of quadrupedal heavily armored, herbivorous, archosaurian reptiles recorded from Upper Triassic deposits. Their remains are found in many parts of the world including North America, South America, Europe, India, Africa, and Greenland (SmaU, 1985; Heckert and Lucas, 1999). Aetosaurs first appeared during the Camian at the beginning of the age of dinosaurs, but became extinct at the end of the Triassic (Norian). They ranged in SVZJQ from Im to 6m in length. Worldwide, there are ten known genera, with seven occurring in the Chinle Formation and Dockum Group of the southwestern United States (Long and Murry, 1995). The North American genera include Desmatosuchus, Typothorax, Paratypothorax, Calyptosuchus, Longosuchus, Stagonolepis, and Stegomus.Item Taxonomy and phylogeny of the Aetosauria (Archosauria: Pseudosuchia) including a new species from the Upper Triassic of Arizona(2014-05) Parker, William Gibson, active 21st century; Rowe, Timothy, 1953-Aetosaurians are a clade of pseudosuchian archosaurs that were globally dispersed during the Late Triassic Epoch. Aetosaurians are characterized by a suite of osteoderms that covered much of the body. These osteoderms are commonly recovered as fossils and possess characteristic surface ornamentation that can be diagnostic for taxa. The abundance of these osteoderms and the ease of identification have made aetosaurians ideal index taxa for Late Triassic biostratigraphy. Of special interest are specimens from South and North America and Europe that have been assigned to the genus Stagonolepis, which have been utilized for correlation of continental sedimentary units and to approximately date the timing of important biotic events. New finds have called the synonymy of these Stagonolepis-like specimens into question, jeopardizing their ability to serve as biochronological markers. Detailed examination of all of the specimens assigned to Stagonolepis robertsoni demonstrates that all of these specimens do not represent the same species. The South American material is assigned to the genera Aetosauroides, Aetobarbakinoides, and Polesinesuchus; the European material to Stagonolepis; and the North American material to Calyptosuchus, Adamanasuchus, and a newly recognized taxon, Scutarx deltatylus. Scutarx deltatylus can be differentiated from other aetosaurians by the presence of a strongly raised, triangular boss, on the posteromedial corner of the paramedian osteoderms. Scutarx deltatylus also preserves the first good skull material from a Stagonolepis-like aetosaur from North America. A dorsoventrally thickened skull roof and an anteroposteriorly short parabasisphenoid further demonstrate the distinctness of this material from that of South America and Europe. A detailed phylogenetic analysis of all known aetosaurians further demonstrates the distinctness of these taxa. This new expanded analysis of 28 taxa and 83 characters recovers Aetosauroides scagliai as the sister taxon to all other aetosaurians. Stagonolepis robertsoni from Scotland does not clade with Stagonolepis olenkae from Poland. Calyptosuchus wellesi is the sister taxon to a clade consisting of Scutarx deltatylus and Adamanasuchus eisenhardtae. However, distribution of autapomorphies across these taxa precludes them from being synonymized. As a result the Stagonolepis-like aetosaurs cannot be used for global scale correlations of Upper Triassic strata, but do appear to be of utility for regional correlations, in particular those between the Chinle Formation and Dockum Group in the American Southwest.