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Pygostyles in Pterosaurs



Gotta hash this again....

  The only pterosaur (and incidentally, the only
non-dinosaurian besides megalancosaurs/drepanosaurs)
with a pygostyle is *Pteranodon*, an affair of about
11 coossified vertebrae that terminate in two distal
prongs possibly formed from the zygapophyses; this
suggests that the uropatagium may have been attached
the entire length of the tail, but I was once of a
speculation that it may have attached a separate
caudal "fin" as in "rhamphorhynchoids" -- I haven't
the time to test either hypothesis, though, or the
resources, yet.

  Also, *Anurognathus*, like all other dimorphodontids
and "rhamphorhynchoids" did not have a pygostyle, or
at least a second-level inference suggests this,
because there is no complete caudal material known for
the animal (and only one specimen); rhamphorhynchoids
have a caudal structure remarkably like that of
dromaeosaurids, with elongated prezygapophyses and
haemal arches (chevrons) overlapping the other caudal
vetrebrae, leaving only the anteriormost five or so
free to flex or such. This may be similar functionally
to a pygostyle, but known animals bearing pygostyles
do not have elongated, overlapping structures
associated, such as *Nomingia*, birds, even the
possible proto-pygostyle in *Caudipteryx*, a condition
oviraptorosaurs share with birds.

  And just to round it off,
megalancosaurs/drepanosaurs have an interesting
spur-like form of the end of the tail, probably from
congealed vertebrae and thus a pygostyle, that may or
may not have served as a brace when climbing or
whatever. Figuring out what _this_ is may be a good
series of test. Maybe Sylvio Renesto would be up to
it....

  Oh, and just for you high-school types: a pygostyle
is a fusion of "pygals", caudal vertebrae lacking
transverse processes and prominent (one text said all)
traces of the neural spine, with the stylus (a rod)
being a fusion of the structures. Free caudals are
just that. A urostyle, unlike the pygal form, is the
opposite, and froms from free caudals fusing into a
rod posterior to the sacrum (and to the sacrum). And
the reason for this little tidbit is a question:
What's the anuran urostyle for?

=====
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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