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Re: Pro(to)avis



James Cunningnam wrote:

Jim, you may be interested in this (if you haven't seen it already):

Gatesy,. S.M. and Dial, K.P. 1996. From frond to fan: Archaeopteryx and the evolution of short-tailed birds. Evolution 50(5): 2037-2048.

Abstract: "Modern birds have extremely short tail skeletons relative to _Archaeopteryx_ and nonavialian theropod dinosaurs. Long- and short-tailed birds also differ in the conformation of main tail feathers making up the flight surface: frond shaped in _Archaeopteryx_ and fan shaped in extant fliers. Mechanisms of tail fanning were evaluated by electromyography in freely flying pigeons and turkeys and by electrical stimulation of caudal muscles in anesthetized birds. Results from these experiments reveal that the pygostyle, rectrices, rectricial bulbs and bulbi rectricium musculature form a specialized fanning mechanism. Contrary to previous models, our data support the interpretation that the bulbi rectricium independently controls tail fanning; other muscles are neither capable of not necessary for significant rectricial abduction. This bulb mechanism permits rapid changes in tail span, thereby allowing the exploitation of a wide range of lift forces. Isolation of the bulbs on the pygostyle effectively decouples tail fanning from a fan movement, which is governed by the remaining caudal muscles. The tail of _Archaeopteryx_, however, differs from this arrangement in several important respects. _Archaeopteryx_ probably had a limited range of lift forces and tight coupling between vertebral and rectricial movement. This would have made the tail of this primitive flier better suited to stabilization than maneuverability. The capacity to significantly alter lift and manipulate and flight surface without distortion may have been two factors favoring tail shortening and pygostyle development during avian evolution."

Ian Paulsen wrote:

What is the pouncing proavis hypothesis?

J.P. Garner, G.K. Taylor, and A.L.R. Thomas. 1999. On the origins of birds: the sequence of character acquisition in the evolution of avian flight. Proceedings of the Royal Society: Biological Sciences. 266(1425):1471-2954.


Abstract: "Assessment of competing theories for the evolution of avian flight is problematic, and tends to rest too heavily on reconstruction of the mode of life of one or a few specimens representing still fewer species. A more powerful method is to compare the sequence of character acquisition predicted by the various theories with the empirical sequence provided by cladistic phylogeny. Arboreal and cursorial theories incorrectly predict the sequence of character acquisition for several key features of avian evolution. We propose an alternative 'pouncing proavis' model for the evolution of flight. As well as being both biologically and evolutionarily plausible, the pouncing proavis model correctly predicts the evolutionary sequence of all five key features marking the evolution of birds."

Cheers

Tim