Morphology of the Neurocentral Junction during Postnatal Growth of Alligator (Reptillia, Crocodylia).

The two main parts of a vertebra, the centrum and neural arch, form independently during early developmental stages in nearly all vertebrates, and they typically fuse together in later growth stages. Fusion between centrum and neural arch is the result of ossification of a thin cartilage layer (neurocentral synchondrosis) between them. The timing of neurocentral fusion varies considerably within the vertebral column and among species, especially in archosaurian reptiles, and may be related to changes in body size and/or locomotion. Despite the importance of neurocentral fusion to our understanding of archosaur evolution, basic information about this process and how it changed through time remains poorly understood. In this dissertation, morphology of neurocentral sutures and vertebrae in crocodilians (Reptilia, Archosauria) is explored. In Chapter 2, the detailed cell- and tissue-level morphology of neurocentral sutures in the vertebrae of Alligator mississippiensis is documented. In chapter 3, complexity of neurocentral sutures are quantified, and changes related to differences in vertebral position, ontogenetic age, and phylogeny are examined. In Chapter 4, allometric changes in vertebrae of Alligator are quantified and investigated in relation to key ontogenetic events. As seen in some craniofacial bones in various vertebrates, neurocentral fusion may affect changes in relative size and shape of certain vertebral structures (e.g., centrum, neural spine, transverse processes, neural canal) during growth. In chapter 5, data examined in crocodilians (chapters 2–4) are applied to various fossil archosaurs from the Early Mesozoic to investigate the origin and evolutionary significance of two unique features of neurocentral sutures, delayed neurocentral fusion and complex neurocentral sutures.Ph.D.GeologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/78850/1/ikejiri_1.pd

A Nomenclature for Vertebral Fossae in Sauropods and Other Saurischian Dinosaurs

The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs), like living birds, was pneumatized by epithelial outpocketings of the respiratory system. Pneumatic signatures in the vertebral column of fossil saurischians include complex branching chambers within the bone (internal pneumaticity) and large chambers visible externally that are bounded by neural arch laminae (external pneumaticity). Although general aspects of internal pneumaticity are synapomorphic for saurischian subgroups, the individual internal pneumatic spaces cannot be homologized across species or even along the vertebral column, due to their variability and absence of topographical landmarks. External pneumatic structures, in contrast, are defined by ready topological landmarks (vertebral laminae), but no consistent nomenclatural system exists. This deficiency has fostered confusion and limited their use as character data in phylogenetic analysis.We present a simple system for naming external neural arch fossae that parallels the one developed for the vertebral laminae that bound them. The nomenclatural system identifies fossae by pointing to reference landmarks (e.g., neural spine, centrum, costal articulations, zygapophyses). We standardize the naming process by creating tripartite names from “primary landmarks,” which form the zygodiapophyseal table, “secondary landmarks,” which orient with respect to that table, and “tertiary landmarks,” which further delineate a given fossa.The proposed nomenclatural system for lamina-bounded fossae adds clarity to descriptions of complex vertebrae and allows these structures to be sourced as character data for phylogenetic analyses. These anatomical terms denote potentially homologous pneumatic structures within Saurischia, but they could be applied to any vertebrate with vertebral laminae that enclose spaces, regardless of their developmental origin or phylogenetic distribution

Anatomy of Camarasaurus Lentus (Dinosauria: Sauropoda) from the Morrison Formation (Late Jurassic),. . .

Two large skeletons of Camarasaurus (Dinosauria. Sauropoda) were excavated from single quarry near Thermopolis, central Wyoming from the Upper Morrison Formation (Kimmeridgian, Late Jurassic). Shed theropod teeth and abundant fossil plants and lignite were also found at the quarry. A complicated stratigraphic sequence based on random patterns and thickness of dark gray mudstone, light gray mudstone, thin sandstone, and carbonate nodule layers suggests that the carcasses of the sauropods were buried under an anastomosing river environment. The two partial skeletons include two partial crania, 15 cervical vertebrae, 14 dorsal vertebrae, two sacra, 51 caudal vertebrae, three scapulocoracoids, two sternal pIates, three humeri, two ulnae, two radii, a partial manus, four ilia, four pubes, four Ischia, four femora, a tibia, a fibula, and many rib and chevron fragments. These bones provide new information on the anatomy of Camarasaurus; particularly, the transit ion from the posterior cervicals to anterior dorsal vertebrae that are significant for the taxonomy and morphological variation in the genus. Moreover, the first chevron is also preserved, which has not been previously described well in any sauropod taxa. An unusual pathology is also found in one of the thoracic ribs. The two Camarasaurus are fully grown individuals based on the completely fused centra and neural arches of all the vertebrae, the closed suture between the scapulocoracoids, and the very rugose articulated surfaces on the limb and girdle bones. The massive short neural arches in the anterior and mid-dorsal vertebrae indicate that the specimens represent C. lentis rather than C. grandis. In addition, gradually expanded neural spines on the anterior caudal vertebrae distinguish C. lentus from C. Supremus and C. grandis, both of which have T-shaped neural spines. Thus, the two Wyoming specimens clarify taxonomic problems in the genus to some degree. One of the individuals is about the same body size as the largest known C. lentus and about 80-85% smaller than C. supremus. In addition, the smaller Camarasaurus from Thermopolis exhibits entheses (ossified tendon) on the neural spines of the posterior dorsal and sacral vertebrae. [More

The braincase of Apatosaurus (Dinosauria, Sauropoda) based on computed tomography of a new specimen, with comments on variation and evolution in sauropod neuroanatomy /

no. 367

Sedimentological and geochemical records of depositional environments of the Late Devonian Chattanooga shale

The Late Devonian is characterized by substantial changes in both land and marine biodiversity. The organic matter-rich Chattanooga Shale was deposited in shelfal waters, thereby serving as an invaluable archive recording changes in land and marine biota as well as terrestrial-marine biogeochemical linkages in the Late Devonian. In the present study, we identified carbon sources and reconstructed depositional environments of the Chattanooga Shale using two outcrops in northeastern Alabama, combining sedimentological and geochemical approaches. The two outcrops share similar sedimentological features (i.e., thinly laminated, fissile, grayish shale strata in the lower part of the outcrop and nearly homogeneous, black, blocky shale in the upper part). The lower part may be assigned to the low to middle units of the Gassaway Member and contains the top of the Dowelltown Member deposited around the Frasnian-Famennian boundary. The upper part is likely equivalent to the upper Gassaway Member. Rock-Eval parameters and the carbon number distribution of normal alkanes show that the organic matter in the Chattanooga Shale is in thermogenic gas window and contains Type II to III kerogen. Low Pristane/Phytane values show that the depositional environment was reducing with interruptions of oxic periods. In the upper part, the values of (Pristane/nC17) / (Phytane/nC18) increase, showing that water may become more oxic. Furthermore, terrestrial organic matter input increased toward the top of the outcrops, as evidenced by increased proportions of long-chain n-alkanes, higher terrigenous/aquatic ratios, lower nC17/nC27 values, and elevated concentration of polycyclic aromatic hydrocarbons derived from terrestrial plants. These data indicate that terrestrial plants became an increasingly important carbon source during the deposition. The presence of pyrosynthetic polycyclic aromatic hydrocarbon compounds can be attributed to prevalent forest fire, in accompanying with the diversification of early land plants in the Eastern Laurasia. These data demonstrate that enhanced inputs of terrestrial organic matter to shelfal waters may have played a vital role in the formation of black shales in the Late Devonian. (Published By University of Alabama Libraries

Variable development of the epipophyseal-prezygapophyseal lamina (eprl) and the divided spinodiapophyseal fossa (sdf) in cervical vertebrae.

<p>The eprl in its most basic form (<b>A</b>) connects the prezygapophysis directly with the epipophysis of the postzygapophysis, dividing the sdf into upper (sdf1) and lower (sdf2) subfossae. More commonly, the eprl is conjoined for at least a portion of its length with two or more laminae (<b>B</b>, <b>C</b>), although sdf1 and sdf2 are still readily identifiable. Blue (sprl, spol, prdl, podl) and yellow (eprl) bars represent single laminae; green bars represent conjoined laminae. Examples of conjoined eprl and the indentification of the fossae they bound are given using the holotypic cervical vertebrae of <i>Erketu ellisoni</i> (IGM 100/1803; <b>D</b>, <b>E</b>) and <i>Nigersaurus taqueti</i> (MNN-GAD 512; <b>F–H</b>) in left lateral view, with diagrammatic representation of laminae and landmarks bounding the sdf. Development of the eprl dividing the sdf is dependent on relative position of landmarks, particularly the separation of the summit of the neural spine (s) and the postzygapophysis (po), as well as the relative positions of the prezygapophysis (pr) and diapophysis (d). Even in taxa with a strongly developed eprl, such as <i>Nigersaurus</i>, the lamina is separate from either the sprl or the podl for only a short distance. Taxa with extremely elongate cervical vertebrae, such as <i>Erketu</i>, may have a slightly different arrangement of connectivity between the eprl, spino-zygapophyseal laminae, and zygapophyseal-diapophyseal laminae, although the presence of the eprl can still be traced. Seventh cervical vertebra of <i>Nigersaurus</i> reversed from right lateral. Not to scale.</p