Could 'four-winged' dinosaurs fly? - latest Nature

[Tim Williams <twilliams_alpha@hotmail.com>]

The latest Nature (17 November, 2005) features a tete-a-tete over whether 
theropods passed through a four-winged stage on the way to evolving flight.  
The aerodynamic capabilities of _Microraptor_, especially the role of those 
"butt-fans", are central to the debate.

Kevin Padian and Kenneth P. Dial (2005).  Origin of flight: Could 
'four-winged' dinosaurs fly?  Nature 438, E3

Arising from: X. Xu et al. Nature 421: 335?340 (2003); F. Zhang & Z. Zhou 
Nature 431: 925 (2004); X. Xu et al. reply; F. Zhang et al. reply

First paragraph: Our understanding of the origin of birds, feathers and 
flight has been greatly advanced by new discoveries of feathered non-avian 
dinosaurs, but functional analyses have not kept pace with taxonomic 
descriptions. Zhang and Zhou describe feathers on the tibiotarsus of a new 
basal enantiornithine bird from the Early Cretaceous of China1. They infer, 
as did Xu and colleagues from similar feathers on the small non-avian 
theropod _Microraptor_ found in similar deposits2, that these leg feathers 
had aerodynamic properties and so might have been used in some kind of 
flight.

Xing Xu, Zhonghe Zhou, Xiaolin Wang, Xuewen Kuang, Fucheng Zhang and Xiangke 
Du (2005).  Origin of flight: Could 'four-winged' dinosaurs fly? (Reply)  
Nature 438: E3-E4.

First paragraph: We agree that a strict biomechanical analysis is needed to 
reconstruct _Microraptor_'s locomotory mode, but we disagree with several of 
Padian and Dial's arguments1. In addition to the six _Microraptor_ specimens 
we described2, other similarly preserved specimens3 have been discovered 
that also had long, asymmetrical pennaceous feathers attached to the 
hindlimbs2. These feathers show features that are functionally correlated 
with flight4. A large, feathery surface on the legs would increase, rather 
than decrease1, drag during running, as evidenced by the reduced or lost 
filamentous integumentary structures on the lower legs of cursorial birds 
and mammals.

Zhonghe Zhou and Fucheng Zhang (2005).  Origin of flight: Could 
'four-winged' dinosaurs fly? (Reply).  Nature 438: E4.

First paragraph: Padian and Dial1 challenge our view that the evolution of 
flight involved a four-winged stage. This disagreement stems from our 
different views on the origin of bird flight and from the methodology we use 
to analyse functional morphology in the non-avian theropod _Microraptor_2 
and in an enantiornithine bird3 from the Early Cretaceous period in China.