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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
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."