Ben Creisler
Recent non-dino papers:
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Birds (Aves) display high metabolic rates and oxygen consumption relative to mammals, increasing reactive oxygen species (ROS) formation. Although excess ROS reduces lifespan by causing extensive cellular dysfunction and damage, birds are remarkably long-lived. We address this paradox by identifying the constitutive activation of the NRF2 master antioxidant response in Neoaves (~95% of bird species), providing an adaptive mechanism capable of counterbalancing high ROS levels. We demonstrate that a KEAP1 mutation in the Neoavian ancestor disrupted the repression of NRF2 by KEAP1, leading to constitutive NRF2 activity and decreased oxidative stress in wild Neoaves tissues and cells. Our evidence suggests this ancient mutation induced a compensatory program in NRF2-target genes with functions beyond redox regulation--including feather development--while enabling significant metabolic rate increases that avoid trade-offs with lifespan. The strategy of NRF2 activation sought by intense clinical investigation therefore appears to have also unlocked a massively successful evolutionary trajectory.
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Madagascar's endemic groundâdwelling leaf chameleons (Brookesiinae: Brookesia Gray, 1865 + Palleon Glaw, et al., Salamandra, 2013, 49, pp. 237â238) form the sister taxon to all other chameleons (i.e., the Chamaeleoninae). They possess a limited ability of color change, a rather dull coloration, and a nonprehensile tail assisting locomotion in the leaf litter on the forest floor. Most Brookesia species can readily be recognized by peculiar spiky dorsolateral projections (âRÃckensÃgeâ), which are caused by an aberrant vertebral structure and might function as body armor to prevent predation. In addition to a pronounced RÃckensÃge, the Antsingy leaf chameleon Brookesia perarmata (Angel, 1933) exhibits conspicuous, acuminate tubercle scales on the lateral flanks and extremities, thereby considerably enhancing the overall armored appearance. Such structures are exceptional within the Chamaeleonidae and despite an appreciable interest in the integument of chameleons in general, the morphology of these integumentary elements remains shrouded in mystery. Using various conventional and petrographic histological approaches combined with ÎCTâimaging, we reveal that the tubercle scales consist of osseous, multicusped cores that are embedded within the dermis. Based on this, they consequently can be interpreted as osteoderms, which to the best of our knowledge is the first record of such for the entire Chamaeleonidae and only the second one for the entire clade Iguania. The combination of certain aspects of tissue composition (especially the presence of large, interconnected, and marrowâfilled cavities) together with the precise location within the dermis (being completely enveloped by the stratum superficiale), however, discriminate the osteoderms of B. perarmata from those known for all other lepidosaurs.
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In vertebrates, the trunk consists of the musculoskeletal structures of the back and the ventrolateral body wall, which together enclose the internal organs of the circulatory, digestive, respiratory and urogenital systems. This review gives an overview on the development of the thoracic and abdominal wall during amniote embryogenesis. Specifically, I briefly summarize relevant historical concepts and the present knowledge on the early embryonic development of ribs, sternum, intercostal muscles and abdominal muscles with respect to anatomical bauplan, origin and specification of precursor cells, initial steps of pattern formation, and cellular and molecular regulation of morphogenesis.
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Significance
The Central Atlantic magmatic province (CAMP) is coincident with the end-Triassic extinction event and several negative carbon isotope excursions (CIEs). Sill emplacements in Brazil would have generated extensive volatiles and degassing due to the contact metamorphism of evaporites, organic-rich shales, and hydrocarbons. Thermogenic carbon release from contact metamorphism represents a plausible source for 12C; however, this has not yet been explored from a carbon cycle approach. This study explores the effects of thermogenic carbon release from CAMP using carbon cycle modeling and shows that it represents a credible source for the negative CIEs at the end-Triassic. It strengthens the hypothesis that the subvolcanic part of a large igneous province is of major importance for understanding carbon cycle disruptions.
Abstract
The Central Atlantic magmatic province (CAMP), the end-Triassic mass extinction (ETE), and associated major carbon cycle perturbations occurred synchronously around the Triassic-Jurassic (T-J) boundary (201 Ma). Negative carbon isotope excursions (CIEs) recorded in marine and terrestrial sediments attest to the input of isotopically light carbon, although the carbon sources remain debated. Here, we explore the effects of mantle-derived and thermogenic carbon released from the emplacement of CAMP using the long-term oceanâatmosphere-sediment carbon cycle reservoir (LOSCAR) model. We have tested a detailed emission scenario grounded by numerous complementary boundary conditions, aiming to model the full extent of the carbon cycle perturbations around the T-J boundary. These include three negative CIEs (i.e., Marshi/Precursor, Spelae/Initial, Tilmanni/Main) with sharp positive CIEs in between. We show that a total of ~24,000 Gt C (including ~12,000 Gt thermogenic C) replicates the proxy data. These results indicate that thermogenic carbon generated from the contact aureoles around CAMP sills represents a credible source for the negative CIEs. An extremely isotopically depleted carbon source, such as marine methane clathrates, is therefore not required. Furthermore, we also find that significant organic carbon burial, in addition to silicate weathering, is necessary to account for the positive Î13C intervals following the negative CIEs.
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Stephen E. Grasby, Xiaojun Liu, Runsheng Yin, Richard E. Ernst & Zhuoheng Chen (2020)
Toxic mercury pulses into late Permian terrestrial and marine environments.
Geology (advance online publication)
doi:
https://doi.org/10.1130/G47295.1https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G47295.1/586523/Toxic-mercury-pulses-into-late-Permian-terrestrialLarge spikes in mercury (Hg) concentration are observed globally at the latest Permian extinction (LPE) horizon that are thought to be related to enhanced volcanic emissions of the Siberian Traps large igneous province (LIP). While forming an effective chemostratigraphic marker, it remains unclear whether such enhanced volcanic Hg emissions could have generated toxic conditions that contributed to extinction processes. To address this, we examined the nature of enhanced Hg emissions from the Siberian Traps LIP and the potential impact it may have had on global ecosystems during the LPE. Model results for a LIP eruption predict that pulses of Hg emissions to the atmosphere would have been orders of magnitude greater than normal background conditions. When deposited into world environments, this would have generated a series of toxic shocks, each lasting >1000 yr. Such repeated Hg loading events would have had severe impact across marine trophic levels, as well as been toxic to terrestrial plant and animal life. Such high Hg loading rates may help explain the co-occurrence of marine and terrestrial extinctions.
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Matthias Ebert, Michael H. Poelchau, Thomas Kenkmann & Bennet Schuster (2020)
Tracing shock-wave propagation in the Chicxulub crater: Implications for the formation of peak rings.
Geology (advance online publication)
doi:
https://doi.org/10.1130/G47129.1https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G47129.1/586527/Tracing-shock-wave-propagation-in-the-ChicxulubThe Chicxulub crater (YucatÃn Peninsula, Mexico) is considered exceptional in many scientific aspects; morphologically it is the only known impact structure on Earth with a well-preserved peak ring. Recent drilling (International Ocean Discovery ProgramâInternational Continental Scientific Drilling Program Expedition 364) into this topographic feature provides insights into the structural properties and complex formation of a peak ring. By means of U-stage microscopy on shocked quartz grains from the granitic section of the recovered drill core, orientations of feather features (FFs) were determined and local principal axis of stress (Ï1) orientations of the shock wave were derived. The FF orientations are strongly confined to a radially outward trend (WNW) relative to the crater center, which emphasizes a link between FF formation and the direction of shock-wave propagation. Thus, FFs represent an excellent tool as a stress-orientation indicator for the shock wave. Our microstructural data set shows that the granitic basement of the peak ring between ~750 and ~1200 m below seafloor behaved as a semi-coherent block above an imbricate thrust zone, and underwent both rotation and local folding during cratering. This validates the block sizes of acoustic fluidization employed in most Chicxulub-scale impact simulations. The folding of the upper part of the granitic basement may have developed by either (1) compression of the crater wall at the transient cavity and/or (2) dragging by the centripetal flow of the overlying crater material.