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James R. Usherwood, Jorn A. Cheney, Jialei Song, Shane P. Windsor, Jonathan P. J. Stevenson, Uwe Dierksheide, Alex Nila & Richard J. Bomphrey (2020)
High aerodynamic lift from the tail reduces drag in gliding raptors.
Journal of Experimental Biology Â223: jeb214809
doi: 10.1242/jeb.214809
https://jeb.biologists.org/content/223/3/jeb214809
Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3âmm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers.
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https://royalsocietypublishing.org/doi/pdf/10.1098/rsbl.2019.0848The repeated evolution of convergent or analogous traits is often used as evidence for adaptive evolution. Squamate reptiles show a high degree of convergence in a variety of morphological traits; however, the evolutionary mechanisms driving these patterns are not fully understood. Here, we investigate the evolution of tail spines, a trait that evolved multiple times in evolutionarily independent clades of lizards. Taking a comparative phylogenetic approach, we use 2877 squamate species to demonstrate that the evolution of spiny tails is correlated with microhabitat use, with species that live in rocky habitats significantly more likely to have evolved spiny tails. In the light of previous behavioural observations, our results suggest that spiny-tailed lizards have an advantage in rocky habitats through predation avoidance, where tail spines are used to prevent extraction from rocky crevices. In concordance with previous research on lizard body armour, our results suggest that the evolution of tail spines is coupled to both a rock-dwelling lifestyle and predator avoidance strategies, and highlight a complex interplay between different selective pressures on the evolution of defensive morphologies in reptiles.
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Body size is one of the most influential traits affecting many ecological and physiological processes across animal and plant taxa. Studies of the environmental factors shaping body size patterns may evaluate either temporal or spatial dimensions. Here, we analyzed body size evolution in the radiation of Anolis lizards across both geographical and temporal dimensions. We used a set of macroecological and macroevolutionary methods to test current and past environmental effects on geographical gradients of body size and its evolutionary rates. First, we test whether a set of current ecological/physiological hypotheses (heat balance, productivity and seasonality) explains spatial body size gradients. Second, we evaluate how tempo (i.e. evolutionary rates) and mode (i.e. evolutionary process) of body size evolution changed through time and the role of paleoâtemperatures on rates of body size evolution during the Cenozoic. We did not find a signature of current environmental variables driving spatial body size gradients. By contrast, we found strong support for a correlation between temperature changes (i.e. climate cooling) during the Cenozoic and rates of body size evolution (i.e. body size diversification). We suggest that patterns of body size evolution in Anolis lizards might be influenced by thermoregulatory behavior across clades and regions.
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Kellen M. Verissimo, Louise N. Perez, Aline C. Dragalzew, Gayani Senevirathne, Sylvain Darnet, Wainna R.B. Mendes, Ciro A.S. Neves, Erika M. dos Santos, Cassia N.S. Moraes, Neil H. Shubin, Nadia .B Froebisch, Josane F Sousa & Igor Schneider (2020)
The West African lungfish provides insights into the evolution of tetrapod tail regeneration.
bioRxiv 2020.02.12.946319
doi:
https://doi.org/10.1101/2020.02.12.946319https://www.biorxiv.org/content/10.1101/2020.02.12.946319v1Salamanders, frog tadpoles, and lizards possess the remarkable ability to regenerate tails. The fossil record suggests that this capacity is an ancestral tetrapod trait, yet its evolutionary history remains unclear. Here we examine tail regeneration in a living representative of the sister group of tetrapods, the West African lungfish Protopterus annectens. We show that, as seen in salamanders, lungfish tail regeneration occurs via formation of a proliferative blastema and restores original structures including muscle, skeleton and spinal cord. Contrary to lizards and similar to salamanders, lungfish regenerate spinal cord neurons and reconstitute dorsoventral patterning of the tail. Similar to salamander and frog tadpoles, we show that Shh is required for lungfish tail regeneration. Through RNA-seq analysis of uninjured and regenerating tail blastema we show that lungfish deploy a genetic program comparable to that of tetrapods, showing upregulation of genes and signaling pathways previously implicated in amphibian and lizard tail regeneration. Furthermore, the tail blastema showed marked upregulation of genes encoding post-transcriptional RNA processing components and transposon-derived genes. Collectively, our study establishes the lungfish as a valuable research system for regenerative biology and provides insights into the evolution of cellular and molecular processes underlying vertebrate tail regeneration.
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The Sinacanthida ordo nov. and Mongolepidida are spine- and scale-based taxa whose remains encompass some of the earliest reported fossils of chondrichthyan fish. Investigation of fragmentary material from the Early Silurian Tataertag and Ymogantau Formations of the Tarim Basin (Xinjiang Uygur Autonomous Region, China) has revealed a diverse mongolepidid and sinacanthid fauna dominated by mongolepids and sinacanthids in association with abundant dermoskeletal elements of the endemic 'armoured' agnathans known as galeaspids.
Micro-computed tomography, scanning electron microscopy and histological sections were used to identify seven mongolepid genera (including Tielikewatielepis sinensis gen. et sp. nov., Xiaohaizilepis liui gen. et sp. nov. and Taklamakanolepis asiaticus gen. et sp. nov.) together with a new chondrichthyan (Yuanolepis bachunensis gen. et sp. nov.) with scale crowns consisting of a mongolepid-type atubular dentine (lamellin). Unlike the more elaborate crown architecture of mongolepids, Yuanolepis gen. nov. exhibits a single row of crown elements consistent with the condition reported in stem chondrichthyans from the Lower Devonian (e.g. in Seretolepis, Parexus). The results corroborate previous work by recognising lamellin as the main component of sinacanthid spines and point to corresponding developmental patterns shared across the dermal skeleton of taxa with lamellin and more derived chondrichthyans (e.g. Doliodus, Kathemacanthus, Seretolepis and Parexus).
The Tarim mongolepid fauna is inclusive of coeval taxa from the South China Block and accounts for over two-thirds of the species currently attributed to Mongolepidida. This demonstrates considerable overlap between the Tarim and South China components of the Lower Silurian Zhangjiajie Vertebrate Fauna.