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Re: Pygostyles in Pterosaurs



  Just a few additional comments and a correction:

I wrote:

<Also, *Anurognathus*, like all other dimorphodontids
and "rhamphorhynchoids" did not have a pygostyle,>

  Larry Febo wrote of the pygostyle of a anurognath, I
assume, based on the Dave Peter's restoration online;
looking at the restoration on the web, I can see where
the confusion arose: the original restoration is much
better quality and detailed, I'm sure, and translation
to a low-res digital form for the net obscures some
details, such as the fine lines between caudals and so
on. There is not fault, here, dude.

<And just to round it off, megalancosaurs/drepanosaurs
have an interesting spur-like form of the end of the
tail ... that may or may not have served as a brace
when climbing or whatever.>

  Similar to the tails in some woodpeckers (Picae) and
hornbills (Bucerotae), which have two long shafts
stiffened for bracing, along with zygodactyl feet
(where the fourth, outer toe is turned backwards). The
structure in the megalancosaurs may have supported a
ceratinous or scaly structure that could dig into bark
and allow the animal to orient its body without
fearing instability on a more-or-less vertical trunk
[I'm imagining silky anteaters, here]. There, some
relatively testable hypotheses....

--------

  And finally, back at the beginning of the post, I
wrote:

<The only pterosaur (and incidentally, the only
non-dinosaurian besides megalancosaurs/drepanosaurs)
with a pygostyle is *Pteranodon*...>

  This is not entirely true, as apparently some other
dinosaurs (ornithischians) may have the condition ...
see below:

<...known animals bearing pygostyles do not have
elongated, overlapping structures associated, such as
*Nomingia*, birds, even the possible proto-pygostyle
in *Caudipteryx*...,>

  Ankylosaurids have a odd, club-like form of the tail
posterior to the tenth or so caudal vertebrae, with
large block-like prezygapophyses overlapping the
proceeding vertebrae for just less than the relative
vertebral centrum; this locks the tail into one long
shaft, and the distal haemal arches in both
nodosaurids and ankylosaurids are fused together, and
in both ankylosaurids, *Nomingia*, and *Sauropelta*,
the distalmost haemals congeal with their respective
vertebrae... The distalmost three or so caudals of
*Sauropelta* (Ostrom, 1970) are functionally one
thing, along with their haemals, and this might
qualify as a pygostyle.

  Similarly, *Shunosaurus* and anklylosaurids
(including shamosaurs) have distal caudals that are
definately fused together and also bear large dermal
plates fused to the caudals, the infamous "clubs" and
"maces." So pygostyles, rather unlike the recent
Barsbold et al. (2000a,b) papers on *Nomingia* suggest
(by abstract and title in the second, descriptive
paper), where pygostyles occur frequently in
dinosaurs. (a basal eusauropod, several maniraptorans,
all Aves, by first-level inference, Ankylosauria,
etc.).

  A nice analysis would be to test if these various
structures bear a common thread, function, origin, and
thus allow an interpretation of the avian pygostyle
(and why *Confuciusornis* can have an 11-15? caudal
pygostyle, without retrices but two in "males").

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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