Ben Creisler
Some recent non-dino papers
Heishanosaurus pygmaeus gen. et sp. nov.
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(The generic name is bit confusing since Heishansaurus (without an "o") is a pachycephalosaur. There are many sources that have used the emended spelling "Heishanosaurus" for the dinosaur.)
Liping Dong, Ryoko Matsumoto, Nao Kusuhashi, Yuanqing Wang, Yuan Wang & Susan E. Evans (2020)
A new choristodere (Reptilia: Choristodera) from an AptianâAlbian coal deposit in China.
Journal of Systematic Palaeontology (advance online public)
DOI: 10.1080/14772019.2020.1749147
https://www.tandfonline.com/doi/full/10.1080/14772019.2020.1749147Choristoderes are a small clade of freshwater aquatic reptiles known from deposits of Jurassic-Miocene age. They show their greatest diversity in the Early Cretaceous of Asia, with seven recorded genera including longirostrine and brevirostine taxa, long- and short-necked taxa, and representatives of both neochoristoderes and non-neochoristoderes. The latter, informal grouping, comprising Monjurosuchus, Philydrosaurus, Hyphalosaurus, Khurendukhosaurus and, probably, Shokawa, is distinguished by the closure of the lower temporal fenestra. This differentiates them from typically diapsid stem choristoderes like the Jurassic Euramerican Cteniogenys and from all neochoristoderes like Champsosaurus and Simoeodosaurus. The recent description of Coeruleodraco jurassicus from the Callovian/Oxfordian of China provided the first example of an Asian non-neochoristodere with an open lower temporal fenestra. Here, we describe a second, geologically younger, genus and species from the Shahai Formation of Badaohao locality in western Liaoning, considered to be Aptian-Albian in age. This adds an eighth choristodere genus to the Early Cretaceous Asian record. The new species shares the diapsid skull morphology of C. jurassicus, demonstrating that a lineage of small, brevirostrine choristoderes with fully diapsid skulls persisted in Asia until the latter part of the Early Cretaceous.
Zoobank: https://zoobank.org:pub:2D0B390A-6291-4C29-A72A-4F6A507C608B
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Although isolated Champsosaurus remains are common in Upper Cretaceous sediments of North America, the braincase of these animals is enigmatic due to the fragility of their skulls. Here, two well-preserved specimens of Champsosaurus (CMN 8920 and CMN 8919) are CT scanned to describe their neurosensory structures and infer sensory capability. The anterior portion of the braincase was poorly ossified and thus does not permit visualization of a complete endocast; however, impressions of the olfactory stalks indicate that they were elongate and likely facilitated good olfaction. The posterior portion of the braincase is ossified and morphologically similar to that of other extinct diapsids. The absence of an otic notch and an expansion of the pars inferior of the inner ear suggests Champsosaurus was limited to detecting low frequency sounds. Comparison of the shapes of semicircular canals with lepidosaurs and archosauromorphs demonstrates that the semicircular canals of Champsosaurus are most similar to those of aquatic reptiles, suggesting that Champsosaurus was well adapted for sensing movement in an aquatic environment. This analysis also demonstrates that birds, non-avian archosauromorphs, and lepidosaurs possess significantly different canal morphologies, and represents the first morphometric analysis of semicircular canals across Diapsida.
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Free pdf:
Free pdf:
https://www.nature.com/articles/s41598-020-63625-0.pdfThe early Permian mesosaurs were the first amniotes to re-invade aquatic environments. One of their most controversial and puzzling features is their distinctive caudal anatomy, which has been suggested as a mechanism to facilitate caudal autotomy. Several researchers have described putative fracture planes in mesosaur caudal vertebrae -- unossified regions in the middle of caudal vertebral centra -- that in many extant squamates allow the tail to separate and the animal to escape predation. However, the reports of fracture planes in mesosaurs have never been closely investigated beyond preliminary descriptions, which has prompted scepticism. Here, using numerous vertebral series, histology, and X-ray computed tomography, we provide a detailed account of fracture planes in all three species of mesosaurs. Given the importance of the tail for propulsion in many other aquatic reptiles, the identification of fracture planes in mesosaurs has important implications for their aquatic locomotion. Despite mesosaurs apparently having the ability to autotomize their tail, it is unlikely that they actually made use of this behaviour due to a lack of predation pressure and no record of autotomized tails in articulated specimens. We suggest that the presence of fracture planes in mesosaurs is an evolutionary relic and could represent a synapomorphy for an as-yet undetermined terrestrial clade of Palaeozoic amniotes that includes the earliest radiation of secondarily aquatic tetrapods.
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News:
Could the oldest marine reptiles drop their tail?
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Also:
Across time, but also across space
Fossils, especially those from marine systems, have long been used to estimate changes in patterns of diversity over time. However, fossils are patchy in their occurrence, so such temporal estimates generally have not included variations due to space. Such a singular examination has the potential to simplify, or even misrepresent, patterns. Close et al. used a spatially explicit approach to measure diversity changes in marine fossils across time and space. They found that, like modern systems, diversity varies considerably across space, with reefs increasing diversity levels. Accounting for this spatial-environmental variation will shed new light on the study of diversity over time.
Abstract
The global fossil record of marine animals has fueled long-standing debates about diversity change through time and the drivers of this change. However, the fossil record is not truly global. It varies considerably in geographic scope and in the sampling of environments among intervals of geological time. We account for this variability using a spatially explicit approach to quantify regional-scale diversity through the Phanerozoic. Among-region variation in diversity is comparable to variation through time, and much of this is explained by environmental factors, particularly the extent of reefs. By contrast, influential hypotheses of diversity change through time, including sustained long-term increases, have little explanatory power. Modeling the spatial structure of the fossil record transforms interpretations of Phanerozoic diversity patterns and their macroevolutionary explanations. This necessitates a refocus of deep-time diversification studies.
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News:
Ocean biodiversity has not increased substantially for hundreds of millions of years -- new study
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Ablation of Chicxulub marine sediments was used to replicate the impact-vapor plume.
The spectra showed similar atomic emissions for the carbonate and anhydrite layers.
Emission lines corresponded to Ca+, Ca, N, O, and C.
Abstract
A plume of vaporized sediments and basement rocks was ejected to the top of atmosphere when a 10â15âkm asteroid impacted on Yucatan in the Southern Gulf of Mexico about 66 million years ago. The Chicxulub impact-vapor plume emitted a flash of light that had clues on the chemistry and degree of vaporization of the target surface material. Here we simulate the asteroid impact by vaporizing marine carbonate sediments cored in the Yaxcopoil-1 borehole in the Chicxulub crater using an intense infrared laser pulse. We investigate two sedimentary layers that represent the most dominant mineral phases of the target sequence: carbonates and sulfates. Their main constituents are 86% calcite and 74% anhydrite, respectively. The laser-induced vapor plumes were produced from each layer in a background simulated late Cretaceus atmosphere (0.16% CO2, 30% O2, and 69.84% N2). Time-resolved spectroscopic analyses from the laser-induced plumes were carried out using experimental and synthetic spectra. The vapor plumes had similar temperatures (â7800âK) at 1âÎs and their spectra showed similar emissions. The spectra contained the following lines in nm: Ca+ (mostly at 393.4 and 396.9 with less prominence at 370.6 and 373.7), Ca (422.7, 430.3, 443.6, 445.5, 527.0, 560.3, 616.4, and 657.3), N (746.8 and 821.6), O (777.7), and C (794.5). Molecular bands were not conspicuous which indicated complete vaporization of the target material by the laser pulse. The contribution of the granitic basement was examined using synthetic spectra. The expected emissions according to their intensities are: Na (589.6), Ca+ (393.4), Al (396.2, 309.3), Ca+ (396.9), Ca (422.7), Na (819.5) and K (766.5, 769.9). The results suggest that the emission corresponded to Ca+ and Ca originated mostly from the volatilization of the marine sediments, and Na, Al, and K from the basement rocks. The physico-chemical evolution of the Chicxulub impact-vapor plume could be deduced by deciphering the temperature and electron density from the emission lines of Ca and Ca+. These physical parameters can be used in gas dynamic models to predict the fluxes and nature of gases, vapors and mineral phases that were introduced into the atmosphere and better assess their impact to the environment and the biosphere.
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