Ben Creisler
Some additional recent non-dino papers
(Don't recall hearing the term "penguin optimum" before...)
Free pdf:
Steven D. Emslie (2020)
Ancient AdÃlie penguin colony revealed by snowmelt at Cape Irizar, Ross Sea, Antarctica.
Geology (advance online publication)
https://doi.org/10.1130/G48230.1https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G48230.1/590932/Ancient-Adelie-penguin-colony-revealed-by-snowmeltThe Ross Sea (Antarctica) is one of the most productive marine ecosystems in the Southern Ocean and supports nearly one million breeding pairs of AdÃlie penguins (Pygoscelis adeliae) annually. There also is a well-preserved record of abandoned penguin colonies that date from before the Last Glacial Maximum (>45,000 14C yr B.P.) through the Holocene. Cape Irizar is a rocky cape located just south of the Drygalski Ice Tongue on the Scott Coast. In January 2016, several abandoned AdÃlie penguin sites and abundant surface remains of penguin bones, feathers, and carcasses that appeared to be fresh were being exposed by melting snow and were sampled for radiocarbon analysis. The results indicate the âfreshâ remains are actually ancient and that three periods of occupation by AdÃlie penguins are represented beginning ca. 5000 calibrated calendar (cal.) yr B.P., with the last occupation ending by ca. 800 cal. yr B.P. The presence of fresh-appearing remains on the surface that are actually ancient in age suggests that only recently has snowmelt exposed previously frozen carcasses and other remains for the first time in ~800 yr, allowing them to decay and appear fresh. Recent warming trends and historical satellite imagery (Landsat) showing decreasing snow cover on the cape since 2013 support this hypothesis. Increased Î13C values of penguin bone collagen further indicate a period of enhanced marine productivity during the penguin "optimum"â, a warm period at 4000-2000 cal. yr B.P., perhaps related to an expansion of the Terra Nova Bay polynya with calving events of the Drygalski Ice Tongue.
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Ryan S. Terrill (2020)
Simultaneous wing molt as a catalyst for the evolution of flightlessness in birds.
American Naturalist (advance online publication)
https://www.amnat.org/an/newpapers/Dec-Terrill.html
Complex features such as vision, limbs, and flight have been lost by many groups of animals. Some groups of birds are more prone to loss of flight than others, but few studies have investigated possible reasons for this variation. I tested the hypothesis that a rare strategy of flight feather replacement is involved in rate variation in the evolution of flightlessness in birds. This strategy involves a simultaneous molt of the flight feathers of the wing, resulting in a temporary flightless condition during molt. I hypothesized that adaptations for this flightless period may serve as preadaptations for permanent flightlessness under conditions that favor permanent loss of flight. I found an elevated rate of loss of flight in lineages with simultaneous wing molt, when compared to loss of flight in lineages without simultaneous wing molt. This may indicate that birds with simultaneous molt are more prepared to adjust quickly to open niches that do not require flight, such as terrestrial niches on island habitats. These results illustrate how molt strategies can influence the long-term evolutionary trajectories of birds, and provides insight into how phenotypic precursors may act as a mechanism of rate variation in the loss of complex traits.
American Naturalist
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Also:
The remote lower reaches of the Rennick Glacier in the far north of Victoria Land hold some of the least explored outcrop areas of the Transantarctic basin system. Following recent international field-work efforts in the Helliwell Hills, we here provide a comprehensive emendation to the regional stratigraphy. Results of geological and palaeontological reconnaissance and of petrographic, geochemical, and palynostratigraphic analyses reveal a stack of three previously unknown sedimentary units in the study area: the Lower Triassic Van der Hoeven Formation (new unit, 115+ m thick) consists mainly of quartzose sandstone and non-carbonaceous mudstone rich in continental trace fossils. The Middle to Upper Triassic Helliwell Formation (new unit, 235 m thick) consists of coal-bearing overbank deposits and volcaniclastic sandstone and yielded typical plant fossils of the Gondwanan Dicroidium flora together with plant-bearing silicified peat. The succession is capped by c. 14 m of the sandstone-dominated Section Peak Formation (?uppermost TriassicâLower Jurassic). Our results enable more detailed correlation of the PalaeozoicâMesozoic successions throughout East Antarctica and into Tasmania. Of particular interest is one section that spans the end-Permian mass extinction interval, which promises to allow detailed reconstructions of high-latitude vegetation dynamics across this critical interval in Earth History.