Henry P. Tsai, ÂMorgan L. Turner, ÂArmita R. Manafzadeh & ÂStephen M. Gatesy (2019)
Contrastâenhanced XROMM reveals in vivo soft tissue interactions in the hip of Alligator mississippiensis.
Journal of Anatomy (advance online publication)
doi:
https://doi.org/10.1111/joa.13101https://onlinelibrary.wiley.com/doi/10.1111/joa.13101Extant archosaurs exhibit highly divergent articular soft tissue anatomies between avian and crocodilian lineages. However, the general lack of understanding of the dynamic interactions among archosaur joint soft tissues has hampered further inferences about the function and evolution of these joints. Here we use contrastâenhanced computed tomography to generate 3D surface models of the pelvis, femora, and hip joint soft tissues in an extant archosaur, the American alligator. The hip joints were then animated using markerâbased XâRay Reconstruction of Moving Morphology (XROMM) to visualize soft tissue articulation during forward terrestrial locomotion. We found that the anatomical femoral head of the alligator travels beyond the cranial extent of the bony acetabulum and does not act as a central pivot, as has been suggested for some extinct archosaurs. Additionally, the fibrocartilaginous surfaces of the alligatorâs antitrochanter and femoral neck remain engaged during hip flexion and extension, similar to the articulation between homologous structures in birds. Moreover, the femoral insertion of the ligamentum capitis moves dorsoventrally against the membraneâbound portion of the medial acetabular wall, suggesting that the inner acetabular foramen constrains the excursion of this ligament as it undergoes cyclical stretching during the step cycle. Finally, the articular surface of the femoral cartilage model interpenetrates with those of the acetabular labrum and antitrochanter menisci; we interpret such interpenetration as evidence of compressive deformation of the labrum and of sliding movement of the menisci. Our data illustrate the utility of XROMM for studying in vivo articular soft tissue interactions. These results also allow us to propose functional hypotheses for crocodilian hip joint soft tissues, expanding our knowledge of vertebrate connective tissue biology and the role of joint soft tissues in locomotor behavior.
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Robert A. Gastaldo, Johann Neveling, John W. Geissman & CindY V. Looy (2019)
Testing the Daptocephalus and Lystrosaurus assemblage zones in a lithostratographic, magnetostratigraphic, and palynological framework in the Free State, South Africa.
PALAIOS Â34(11): 542-561
doi:
https://doi.org/10.2110/palo.2019.019https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/34/11/542/574685/TESTING-THE-DAPTOCEPHALUS-AND-LYSTROSAURUSThe vertebrate-fossil record in the Karoo Basin has served as the accepted model for how terrestrial ecosystems responded to the end-Permian extinction event. A database of several hundred specimens, placed into generalized stratigraphies, has formed the basis of a step-wise extinction scenario interpreted by other workers as spanning the upper Daptocephalus (=Dicynodon) to Lystrosaurus Assemblage Zones (AZ). Seventy-three percent of specimens used to construct the published model originate from three farms in the Free State: Bethel, Heldenmoed, and Donald 207 (Fairydale). The current contribution empirically tests: (1) the stratigraphic resolution of the vertebrate record on these farms; (2) whether a sharp boundary exists that delimits the vertebrate assemblage zones in these classic localities; and (3) if the Lystrosaurus AZ is of early Triassic age. We have used a multi-disciplinary approach, combining lithostratigraphy, magnetostratigraphy, vertebrate biostratigraphy, and palynology, to test these long-held assumptions.
Previously reported vertebrate-collection sites have been physically placed into a litho- and magnetostratigraphic framework on the Bethel and Heldenmoed farms. The reported assemblage-zone boundary is used as the datum against which the stratigraphic position of vertebrates is compared and a preliminary magnetostratigraphy constructed. We find specimens of the Daptocephalus AZ originate in the Lystrosaurus AZ (as currently defined) and vice versa, and discrepancies between reported and field-checked stratigraphic positions below or above the assemblage-zone boundary often exceed 30 m. Hence, the utility of the data set in defining a sharp or abrupt biozone boundary is questionable. We further demonstrate the presence of a stratigraphically thick reverse polarity magnetozone that encompasses the reported assemblage-zone boundary, implying that these rocks are not correlative with the end-Permian event, which is reported to lie in a normal polarity chron. A latest Permian age is supported by palynological data from the Lystrosaurus AZ on the Donald 207 (Fairydale) farm, with equivalence to Australian (APP602) and Eastern Cape Province assemblages. We conclude that the turnover from the Daptocephalus to Lystrosaurus Assemblage Zones is more protracted than envisioned, it is not coincident with the end-Permian event as recognized in the marine realm, and little evidence exists in support of a three-phased extinction model based on vertebrate assemblages in the Karoo Basin.
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A.D. Muscente, ÂRowan C. Martindale, James D. Schiffbauer, Abby L. Creighton & Brooke A. Bogan (2019)
Taphonomy of the Lower Jurassic Konservat-LagerstÃtte at Ya Ha Tinda (Alberta, Canada) and its significance for exceptional fossil preservation during oceanic anoxic events.
PALAIOS (2019) 34 (11): 515-541.
doi:
https://doi.org/10.2110/palo.2019.050https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/34/11/515/574686/TAPHONOMY-OF-THE-LOWER-JURASSIC-KONSERVAT Konservat-LagerstÃtten provide the most complete snapshots of ancient organisms and communities in the fossil record. In the Mesozoic, these deposits are rarely found in marine facies outside Oceanic Anoxic Event (OAE) intervals, suggesting that OAEs set the stage for exceptional fossil preservation. Although anoxia does not guarantee survival of non-biomineralized tissues or articulated skeletons, other OAE phenomena may promote their conservation. Here, we test this hypothesis with a taphonomic analysis of the Konservat-LagerstÃtte in the black shales and siltstones of the Jurassic Fernie Formation at Ya Ha Tinda (Alberta, Canada). This deposit contains crustacean cuticles, coleoid gladii with ink sacs and mantle tissues, and articulated skeletons of fish, crinoids, and ichthyosaurs. The fossils were preserved in the Pliensbachian and Toarcian (Early Jurassic) when euxinic conditions were common in the area, in part, due to the ~183 Ma Toarcian OAE. Some of the fossils contain carbonaceous material, but the majority consists of apatite minerals, and phosphatic gladii demonstrate that some animals were preserved through secondary phosphate mineralization. Phosphatization generally occurs within phosphate-rich sediment, but oceanic anoxia causes sediment to release phosphorus and prevents animals from colonizing seafloor habitats. Accordingly, we propose that the animals were preserved during brief episodes of bottom water oxia and/or dysoxia, when the environment would have been most favorable to benthic communities and phosphate mineralization. In this setting, phosphatization may have been fueled by phosphate delivery from continental weathering in response to climatic warming, ocean upwelling of eutrophic water, and/or nutrient trapping by anoxia in the basin.
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Over the past 3â4 decades, coincident with global warming and atmospheric CO2 increase, Arctic sea ice has significantly decreased in its extent as well as in thickness. When extrapolating this alarming trend, the central Arctic Ocean might become iceâfree during summers within about the next 2â5 decades. Paleoclimate records allow us to better understand the processes controlling modern climate change and distinguish between natural and anthropogenic forcing. In this context, detailed studies of the earlier Earth history characterized by a much warmer global climate with elevated atmospheric CO2 concentrations are important. The main focus of this review paper is the longâterm late MesozoicâCenozoic Arctic Ocean climate history from Greenhouse to Icehouse conditions, with special emphasis on Arctic sea ice history. Starting with some information on the Cretaceous Arctic Ocean climate, this paper will concentrate on selected results from IODP Expedition 302 (ACEX), the first scientific drilling in the permanently iceâcovered Arctic Ocean, dealing with the Cenozoic climate history. While these results from ACEX were unprecedented, key questions related to the Cenozoic Arctic climate history remain unanswered, largely due to the major midâCenozoic hiatus (if existing) and partly to the poor recovery of the ACEX record. Followingâup ACEX and its cuttingâedge science, a second scientific drilling on Lomonosov Ridge with a focus on the reconstruction of the continuous and complete Cenozoic Arctic Ocean climate history, has currently been proposed and scheduled as IODP Expedition 377 for 2021.