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Re: No Subj. (long feathers)



In a message dated 11/22/1996 8:43:08 PM, longrich@stardot.com (Nick
Longrich) wrote:

> In Archaeopteryx the tail is highly flexible in the vertical plane,
> in Rhamphorhynchus, through the horizonal plane.  Wellnhofer shows
> five different rhamph tails but he also attributes them to five
> different species of Rhamphorhnychus. 

Granted the base of a rhamphorhynchoid tail is the only flexible portion of
its caudal anatomy, but it is not particularly flexible in the horizontal
plane. Unlike dinos and lizards, rhamphs have a much reduced caudofemoral
muscle complex, as evidenced by reduced or missing caudal transverse
processes and hemal arches. These disappear entirely in pterodactloids.
Hence, there is almost no muscle to pull the tail horizontally. Epaxial
muscle attachment points do remain so dorsal flexion of the tail in
pterosaurs may have been the only movement possible there. C. Bennett noticed
this in Pteranodon with its strange duplex centra.

The five different species of Rhamphorhynchus turn out to be growth stages.
The shape of the vane grows until reaching sexual maturity, which is a sure
sign of a decoration, not an aerodynamic "rudder". 

> I should mention that GSP's drawing of Parksosaurus shows long
> vertebral extensions/ossified tendons (don't know which they are
> here.

Good observation. Stiff tails, as you noted elsewhere, are also seen on
dromaeosaurids, and other TERRESTRIAL diapsids.  Tim Hamley did a nice paper
showing that bipedal lizard tails are thinner, longer and stiffer, although
not as thin, long and stiff as in early pterosaurs.  

David Peters