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Atolchelys, new turtle from Cretaceous of Brazil + hummingbird wing efficiency



Ben Creisler
bcreisler@gmail.com

A couple of recent non-dino papers that may be of interest:

Pedro S. R. Romano, Valéria Gallo, Renato R. C. Ramos and Luzia Antonioli (2014)
Atolchelys lepida, a new side-necked turtle from the Early Cretaceous
of Brazil and the age of crown Pleurodira.
Biology Letters 10 no. 7 20140290
doi: 10.1098/rsbl.2014.0290
http://rsbl.royalsocietypublishing.org/content/10/7/20140290.abstract


We report a new pleurodiran turtle from the Barremian Morro do Chaves
Formation, Sergipe-Alagoas Basin, Brazil. We tested the phylogenetic
position of Atolchelys lepida gen. et sp. nov. by including it in a
comprehensive cladistic analysis of pleurodires. The new species is a
basal member of Bothremydidae and simultaneously the oldest
unambiguous crown Pleurodira. The biogeographic and
chronostratigraphic significance of the finding has implications for
the calibration of molecular clocks studies by pushing back the
minimum age of crown Pleurodira by more than 12 Ma (ca 125 Ma). The
reanalysis of Pelomedusoides relationships provides evidence that the
early evolution and relationships among the main lineages of
side-necked turtles can be explained, at least partially, by a
sequence of vicariance events.

===


Jan W. Kruyt, Elsa M. Quicazán-Rubio, GertJan F. van Heijst, Douglas
L. Altshuler, and David Lentink (2014)
Hummingbird wing efficacy depends on aspect ratio and compares with
helicopter rotors.
Journal of the Royal Society Interface. 2014 11 20140585;
doi:10.1098/rsif.2014.0585
http://rsif.royalsocietypublishing.org/content/11/99/20140585

Hummingbirds are the only birds that can sustain hovering. This unique
flight behaviour comes, however, at high energetic cost. Based on
helicopter and aeroplane design theory, we expect that hummingbird
wing aspect ratio (AR), which ranges from about 3.0 to 4.5, determines
aerodynamic efficacy. Previous quasi-steady experiments with a wing
spinner set-up provide no support for this prediction. To test this
more carefully, we compare the quasi-steady hover performance of 26
wings, from 12 hummingbird taxa. We spun the wings at angular
velocities and angles of attack that are representative for every
species and measured lift and torque more precisely. The power
(aerodynamic torque × angular velocity) required to lift weight
depends on aerodynamic efficacy, which is measured by the power
factor. Our comparative analysis shows that AR has a modest influence
on lift and drag forces, as reported earlier, but interspecific
differences in power factor are large. During the downstroke, the
power required to hover decreases for larger AR wings at the angles of
attack at which hummingbirds flap their wings (p < 0.05). Quantitative
flow visualization demonstrates that variation in hover power among
hummingbird wings is driven by similar stable leading edge vortices
that delay stall during the down- and upstroke. A side-by-side
aerodynamic performance comparison of hummingbird wings and an
advanced micro helicopter rotor shows that they are remarkably
similar.

news story:
http://phys.org/news/2014-07-tiny-uavs-hummingbirds.html