Ben Creisler
Some recent non-dino papers:
Allodaposuchus precedens is a basal member of Eusuchia, which was established almost a century ago on a set of cranial and postcranial fragmentary remains from the lower Maastrichtian of VÄlioara, Romania. It was the first described member and type species of Allodaposuchidae, a recently described European clade representing one of the nearest outgroups to Crocodylia. Although our understanding of the group has expanded in recent years through the description of new forms, a review of Al. precedens is needed. The detailed revision of the classical material from VÄlioara, including cranial and postcranial remains, and a comparison with the nearly complete skull from the Romanian synchronous locality of Oarda de Jos, allows us to emend the diagnosis for Al. precedens.
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Provelosaurus americanus from the Guadalupian of Brazil, is the only species of pareiasaur known from South America and its studies are limited to anatomical descriptions. Here, we examined the microstructure of limb bones, a rib fragment and osteoderms of P. americanus, aiming to answer questions related to its paleobiology. The bone tissues of this specimen comprise poorly vascularised parallel-fibred bone interrupted by growth marks indicating slow, cyclical growth. This is consistent with the pattern found in other pareisaurs from South Africa. However, the space between the LAGs are irregular and there is no clear decreasing in vascularity toward the periphery of the bone, suggesting that it did not reach skeletal maturity. The highest number of LAGs was found in the rib, suggesting that our sample lived a minimum of fifteen years. The osteoderms present a trilaminar structure consisting of a diploe composed of a cancellous core surrounded by two cortical layers. A diploe is absent from the osteoderms of previously studied South African pareiasaurs. The osteogenesis of the osteoderms is intramembraneous, but a metaplastic ossification during the early developmental stage cannot be entirely discarded, due to extensive remodeling in the central core that could have destroyed potential metaplastic tissue.
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Free pdf:
Erica K. Baken Â& ÂDean C. Adams (2019)
Macroevolution of arboreality in salamanders.
Ecology and Evolution (advance online publication)
doi:
https://doi.org/10.1002/ece3.5267https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.5267Free pdf:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/ece3.5267Evolutionary theory predicts that selection in distinct microhabitats generates correlations between morphological and ecological traits, and may increase both phenotypic and taxonomic diversity. However, some microhabitats exert unique selective pressures that act as a restraining force on macroevolutionary patterns of diversification. In this study, we use phylogenetic comparative methods to investigate the evolutionary outcomes of inhabiting the arboreal microhabitat in salamanders. We find that arboreality has independently evolved at least five times in Caudata and has arisen primarily from terrestrial ancestors. However, the rate of transition from arboreality back to terrestriality is 24 times higher than the converse. This suggests that macroevolutionary trends in microhabitat use tend toward terrestriality over arboreality, which influences the extent to which use of the arboreal microhabitat proliferates. Morphologically, we find no evidence for an arboreal phenotype in overall body proportions or in foot shape, as variation in both traits overlaps broadly with species that utilize different microhabitats. However, both body shape and foot shape display reduced rates of phenotypic evolution in arboreal taxa, and evidence of morphological convergence among arboreal lineages is observed. Taken together, these patterns suggest that arboreality has played a unique role in the evolution of this family, providing neither an evolutionary opportunity, nor an evolutionary dead end.
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How K-T crisis is recorded in lacustrine system?
Is carbonate Î13C negative anomaly recording the K-T necessarily a shut-down of paleoproductivity?
K-T crisis has a significant impact on lacustrine organic matter distribution (TOC, HI).
Conceptual model for organic carbon enrichment in lacustrine sedimentary systems
Abstract
In this study, an integrated approach was applied using available sedimentary, geochronology, geochemical and isotopic datasets to better understand the complex interactions between production, destruction, and dilution processes that characterize the organic-rich sediments dynamic across the K-T boundary in a lacustrine system. This approach was tested here on the Late Cretaceous to Early Cenozoic Yacoraite Formation, a typical lacustrine source rock from the Salta rift Basin (NW Argentina). The Yacoraite Formation corresponds to a mixed carbonate-siliciclastic lacustrine sedimentary system, deposited during the sag phase (post-rift). We demonstrated here that new ashes U-Pb dating tie the K-T boundary during the deposition of the Yacoraite Formation.
The Yacoraite Formation recorded major climate changes that can be documented in terms of catchment dynamic, erosion processes, carbonate accumulation trends, lacustrine dynamic and source rock quality. The pattern of organic carbon enrichment in the Yacoraite Formation illustrates how a biological pump came across a major climatic change. The background organic matter correspond to Type I dominated by algal growth (mean HI 600â800âmgHC/gTOC, TOC0 1â2âwt%). The K-T boundary was the climax of a climate change initiated ca. 0.3âMyr before and induced a major change in the catchment weathering processes, which temporally corresponds to the accumulation of poor quality source rock intervals (TOC0âââ0.2âwt% and HIâ<â50âmgHC/gTOC) in these series. The K-T boundary is highlighted by the main negative anomaly in Î13C of the carbonate deposits of the Yacoraite Formation. It was followed by a major pulse in paleoproductivity, itself followed by a major pulse in TOC0 (10â15âwt%) under anoxia conditions. In ca. 0.2âMyr the lacustrine dynamic and its related organicâcarbon enrichment resumed to their initial setting, just prior to the preluding K-T boundary climate change. Results suggest that the Yacoraite Formation can be considered as a world-class example to illustrate how the K-T boundary is recorded in lacustrine sediments.