Thursday, September 19, 2013

Wind tunnel to test airworthiness of the feathered dinousaurs

Fossil discoveries over the last decade have shown that many dinosaurs had feathers, including
Yutryannus huali, a 30-ft long relative
of T-Rex. Credit: The Mirror
dinosaurs which were obviously not flight-worthy (see picture). So in the fossil finds that appear more and more bird-like, it's still an ongoing question about whether and when that evolutionary lineage achieved flight. One especially old fossil and candidate ancestor, Microraptor  had respectable feathering on all four limbs plus the tail. This early bird-like dinosaur, if it could fly, would suggest that ancestors of birds had four wings, before two-winged forms arose. But there are no present-day examples of four-winged flying creatures, so whether and how this critter flew is a real puzzle. So several groups have made scale models and examined their aerodynamic properties.
A scale model of Microraptor
(from Alexander et al.)
In 2010, Alexander et al. made a foam model, based on a bones from an individual Microraptor fossil, and even trimmed modern bird feathers to recapitulate the fossil plumage.  They then tweaked the angle of attack for the wings or tail and launched it from a catapault to compare flights.
Alexander et al. found that their Microraptor model was at a minimum, a very stable glider, but probably not capable of  active flight.
More recently, Dyke et al. , tested their own model in a wind tunnel. Similarly to Alexander et al., Dyke et al.  concluded that Microraptor probably could glide fairly well. Their results support the idea that the ancestors of birds employed four feathered limbs.
This conclusion validates a 1915 prediction by William Beebe that the lineage leading to modern birds included a 4-winged ancestor. Beebe based his prediction on his observation of long leg feathers in some modern bird breeds-- and by a close look at the famous early bird fossil, Acheropteryx.

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