Academic literature on the topic 'Transitional vertebra'

Thesis (M.A.)--University of Missouri-Columbia, 2005.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 14, 2006) Includes bibliographical references.

Bibliography: leaves 145-162.<br>This study applies morphometric analyses to the thoracic vertebral column of primates. Vertebral counts are conducted and vertebral patterns examined. The sample for morphometric measurements consists of 112 humans, 27 gorillas, 22 champanzees, 8 orang-utans, 68 vervets and 77 baboons but for the counts the numbers are much higher. The six species exhibit orthograde (human), semi-orthograde (chimpanzee and gorilla), pronograde (baboon and vervet) and suspensory (orang-utan) patterns of locomotion. Measurements of vertebral components are taken on the 7th to 21st vertebrae (C7-L2 in humans). Various ratios are calculated and standardised by the species body weight. The Spearman Rank Correlation Test and the Chi-square Test indicate no sexual dimorphism in respectively morphometric and counts data, and therefore both sexes are pooled.

With the transition from water to land in early tetrapods, and with transitions to secondarily aquatic habits in numerous tetrapod lineages, the functions of the vertebral column were transformed. Morphological changes in the vertebral column are a major mechanism by which vertebrates accommodate changes in locomotor forces. Although morphometric measurements from vertebrae have been correlated with axial mechanics and locomotor behaviour in numerous extant taxa, few studies have sought to test or apply these principles in non-mammalian tetrapods. In my thesis, I reconstructed the vertebral mechanics of fossil taxa that represent intermediate stages in water/land transitions of their lineages. Study taxa were the basal tetrapod Pederpes finneyae, which is one of the earliest known tetrapods to show indications of terrestrial adaptation, and three extinct crocodylomorphs, Terrestrisuchus, Protosuchus, and Pelagosaurus, which span the spectrum from fully terrestrial to primarily aquatic. I used a combination of morphometric measurements and 3D virtual models of bone morphology to estimate intervertebral joint stiffness and range of motion. For comparison, I also reconstructed the vertebral mechanics of four related extant taxa. Correlations between vertebral morphometrics and axial stiffness were statistically tested in (cadaveric) modem crocodylians, and I validated my methodology by comparing my results with data from extant taxa. My results reveal similarities and differences between the two lineages. Intervertebral joint compliance and range of motion tended to decrease with adaptation for terrestrial locomotion, as expected, but this trend seems to have reversed in later forms. Additionally, vertebral mechanics may have been largely controlled by different structural mechanisms in different lineages. The relationship between biomechanics of vertebrae and environment appears to be more complex than previously supposed. However, approaches that combine experimental measurements from extant animals, thorough analysis of fossil morphology, and explicit phylogenetic considerations have the potential to greatly improve locomotor reconstructions of extinct taxa.

L’estudi del registre sedimentari i paleontològic del fini-Carbonífer, Permià i Triàsic continentals dels Pirineus Catalans han permès caracteritzar-ne l’evolució paleoambiental i paleoclimàtica i la seva repercussió sobre els ecosistemes terrestres durnt la transició Paleozoic–Mesozoic. Aquesta transició, marcada per diversos canvis climàtics i extincions en massa, s’ha analitzat mitjançant un estudi multidisciplinari. Les diverses campanyes de camp han resultat en el descobriment de fins a deu noves localitats amb restes fòssils, principalment amb icnites de tetràpodes (de les quals se’n fa especial èmfasi), però també amb restes òssies, traces fòssils d’invertebrats i plantes. Fins al present treball es coneixien molt pocs jaciments de petjades d’aquestes edats als Pirineus Catalans. L’elaboració de columnes estratigràfiques i cartografies de detall ha permès establir la successió espacio-temporal dels jaciments i de les unitats geològiques corresponents (unitats deposicionals definides en treballs anteriors). L’estudi conjunt d’icnites i fàcies contribueixen a realitzar anàlisis paleoambientals. L’estudi del registre fòssil ha implicat l’establiment de diferents biozonacions, que s’ha complementat amb anàlisis paleomagnètiques, cicloestratigràfiques, mineralògiques i elementals. El Carbonífer superior s’ha documentat a partir de l’associació de plantes de la Unitat Grisa, que indiquen una edat d’Estefanià C. Les dades sedimentològiques i de paleosòls indiquen un clima humit amb curts períodes de sequera. El trànsit Carbonífer–Permià (Unitat de Trànsit) ve marcat per un increment en l’estacionalitat i l’aridesa. La manca de marcadors cronològics als afloraments estudiats no permet precisar l’edat de la unitat. El Permià inferior constitueix l’inici de les successions de red-beds. Els paleosòls dels dipòsits volcanosedimentaris de la Unitat Roja Inferior i l’absència de carbó denoten una aridificació del clima i una estacionalitat marcada. Els esporàdics intervals més humits, representats per sistemes fluvials meandriformes i dipòsits derivats d’aigua d’escolament superficial, contenen una icnoassociació de tetràpodes característica de l’Artinskià i constituïda per: Batrachichnus salamandroides, Limnopus isp., cf. Amphisauropus, cf. Ichniotherium, Dromopus isp., cf. Varanopus, Hyloidichnus isp., Dimetropus leisnerianus i tres tipus de Characichnos (traces fòssils de natació). Les traces fòssils d’artròpodes (especialment Rusophycus i Acripes) també són comunes. El registre del Permià mitjà denota unes condicions climàtiques humides i estacionals. El sistema al·luvial distal de la Unitat Roja Superior inferior ha lliurat poques restes fòssils. La presència d’una vèrtebra assignada al grup dels casèids suggereix una edat de Wordià inferior i, juntament amb les icnites de tetràpode documentades en treballs previs, constata un reemplaçament de faunes. El Permià superior es caracteritza per un clima semi-àrid, tal com indiquen les dades sedimentològiques, mineralògiques i elementals de la Unitat Roja Superior superior. El sistema de playa-lake o lacustre efímer mostra un control orbital de la sedimentació. La icnoassociació de tetràpodes documentada marca un reemplaçament de les faunes del Permià mitjà, possiblement lligat a una extinció. El Triàsic Inferior i Mitjà està representat pel sistema fluvial (de rius braided a meandriformes i planes d’inundació) de la unitat en fàcies Buntsandstein, que conté una icnoassociació de tetràpodes formada per: Prorotodactylus mesaxonichnus (erigida com a nova icnoespècie), cf. Rotodactylus, Rhynchosauroides cf. schochardti, Rhynchosauroides i chirotheriids indeterminats, un morfotip indeterminat (Morfotip A) i dos tipus de Characichnos associats a la nova icnoespècie i als chirotheriids. Aquest registre fòssil es complementa amb la presència de dues dents d’arcosauromorf i marca la recuperació dels ecosistemes terrestres després de l’extinció de finals del Permià, amb els arcosauromorfs com a grup cabdal. El registre continu als trànsits Carbonífer–Permià i Permià–Triàsic (fins ara desconegut al sudoest europeu), així com també la inesperada riquesa fòssil, fa dels Pirineus Catalans una regió de referència a nivell global per comprendre alguns dels canvis més dràstics de la història de la Terra.<br>The sedimentary and paleontological record study of the terrestrial end-Carboniferous, Permian and Triassic from the Catalan Pyrenees allowed to characterize its paleoenvironmental and paleoclimatic evolution and their influence on the terrestrial ecosystems during the Paleozoic–Mesozoic transition. This transition, featured by several climatic changes and mass extinctions, has been analyzed in a multidisciplinary study. Diverse fieldworks have resulted in the discovery of up to ten new fossil localities, mainly bearing tetrapod ichnites (here especially emphasized), but also bearing bone remains, invertebrate trace fossils and plants. Until the present work, few fossil footprint sites were known from these ages in the Catalan Pyrenees. The detailed stratigraphic columns and cartography allowed to establish the spatio-temporal succession of fossil sites and of the corresponding geological units (depositional units defined in previous works). The coupled study of ichnites and facies contribute to carry out paleoenvironmental analyses. The study of the fossil record implied the establishment of different biozonations, which have been complemented with paleomagnetic, cyclostratigraphic, mineralogical and elemental analyses. The late Carboniferous has been documented by the Grey Unit plant assemblage, indicating a Stephanian C age. The sedimentological and paleosol data point to a humid climate with short dry periods. The Carboniferous–Permian transition (Transition Unit) is featured by increases in seasonality and aridity. The lack of chronological markers in the studied outcrop precludes to clarify the age of the unit. The early Permian constitutes the beginning of the red-bed successions. Paleosols developed in the Lower Red Unit volcanosedimentary deposits and the absence of coal denote climate aridification and strong seasonality. Sporadic relatively humid intervals, depicted by meandering fluvial systems and deposits derived from unconfined runoff water, yield a tetrapod ichnoassemblage characteristic of the Artinskian and composed of: Batrachichnus salamandroides, Limnopus isp., cf. Amphisauropus, cf. Ichniotherium, Dromopus isp., cf. Varanopus, Hyloidichnus isp., Dimetropus leisnerianus and three types of Characichnos (swimming trace fossils). Arthropod trace fossils (especially Rusophycus and Acripes) are also common. The middle Permian record denotes humid climatic conditions and seasonality. Few fossil remains have been reported from the lower Upper Red Unit distal alluvial system. The presence of a vertebra assigned to the caseid group suggests an early Wordian age and, together with tetrapod ichnites documented in previous works, a faunal replacement is confirmed. The late Permian is characterized by a semi-arid climate, as indicated by the sedimentological, mineralogical and elemental data of the upper Upper Red Unit. Deposits of the playa-lake or ephemeral lacustrine system show orbital forcing during sedimentation. The documented tetrapod ichnoassemblage marks a replacement of the middle Permian faunas, possibly linked to an extinction. The Early and Middle Triassic is recorded by the fluvial system (from braided to meandering rivers and floodplains) of the Buntsandstein facies unit, which yields a tetrapod ichnoassemblage composed of: Prorotodactylus mesaxonichnus (erected as a new ichnospecies), cf. Rotodactylus, Rhynchosauroides cf. schochardti, undetermined Rhynchosauroides and chirotheriids, an undetermined Morphotype A and two types of Characichnos associated to the new ichnospecies and to chirotheriids. This fossil record is complemented with the presence of two recovered archosauromorph teeth and is indicative of the terrestrial ecosystems recovery after the end-Permian mass extinction, being archosauromorphs a relevant group. The continuous record throughout the Carboniferous–Permian and Permian–Triassic transitions (so far unknown from southwestern Europe), as well as the unsuspected fossil richness, make the Catalan Pyrenees a reference region worldwide to untangle some of the most drastic changes of Earth history.

Molecular aspects of nitrogen metabolism in vertebrates is an interesting area of physiology and evolution to explore due to the different ways in which animals excrete nitrogenous waste as they transition from an aquatic to a terrestrial lifestyle. Two main products of nitrogen metabolism in fishes are ammonia and urea. Ammonia is produced during protein catabolism and build up of ammonia is toxic. Some aquatic vertebrates convert ammonia into a less toxic compound urea via de novo synthesis through the ornithine-urea cycle (O-UC). Five enzymes are involved in the O-UC: carbamoyl phosphate synthetase (CPS), ornithine carbamoyl transferase (OCT), argininosuccinate synthetase (ASS), argininosuccinate lyase (ASL), and arginase (ARG). An accessory enzyme, glutamine synthetase (GS) also participates in the "fish-type" O-UC. Teleosts excrete ammonia passively over their gills into the aquatic environment. The teleost, Opsanus beta, has been shown to increase urea production after 48 hours of crowding. This thesis explored how crowding stress affected nitrogen metabolite levels of ammonia and urea and O-UC gene expression and enzyme activity in O. beta. Lungfishes while in an aquatic environment avoid ammonia toxicity by releasing excess ammonia across their gills, but when stranded on land they produce urea through the O-UC. Urea production via the O-UC has a metabolic cost of at least four ATP molecules. This thesis explored the response of a lungfish, Protopterus annectens, to six days of aerial exposure and re-immersion conditions by measuring concentrations of O-UC mRNA expression and enzyme activity and nitrogen metabolites ammonia and urea. CPS acts as the entry point to the O-UC and based on enzymatic studies, most aquatic vertebrates utilize one isoform of this enzyme (CPSIII) while terrestrial vertebrates utilize a different isoform of this enzyme (CPSI). Lungfishes are a particularly interesting group of air-breathing fishes, not only because of their link to the origins of tetrapods, but also because CPS I may have originated within this group. Both CPS III and CPS I have been enzymatically described within this group. This thesis uses phylogenetics to investigate how CPS nucleotide sequences in lungfishes evolved compared to other vertebrates.