Re: Oviraptorosaurs as prehistoric "peacocks"

[Tim Williams <tijawi@gmail.com>]

Thomas R. Holtz, Jr. <tholtz@umd.edu> wrote:

> And is associated in the living forms (at least) with the development of
> the retricial bulb, which may have been absent outside euornithines.


Yes, tail-fanning in modern birds is controlled solely by the
rectricial bulbs (bulbi rectricium).  This is a complex structure
composed of fatty and muscular tissue that encases the pygostyle, and
holds and moves the rectrices.  Basal euornitheans/ornithuromorphs
such as _Hongshanornis_ and _Yixianornis_ preserve evidence of a
tail-fan, in the shape and arrangement of the rectrices.  These birds,
along with crown birds, also have a very short pygostyle.  It is
assumed that the presence of a tail-fan is correlated with the
development of rectricial bulbs, and is an innovation unique to
Euornithes/Ornithuromorpha.


By contrast, the pygostyles of confuciusornithids, enantiornitheans
and oviraptorosaurs tend to be long and blade-like or rod-like.
_Similicaudipteryx_ had at least a dozen pairs of pennaceous rectrices
along the tail, whereas confuciusornithids and enantiornitheans had
(at most) one or two pairs of streamer-like rectrices associated with
the pygostyle.  I like the hypothesis (Gatesy, 2001) that
coossification of the distal caudal skeleton into a pygostyle was
originally associated with tail reduction, and was only co-opted much
later for an aerodynamic function (when rectricial bulbs and
tail-fanning were invented).






Cheers

Tim