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Archie skull pneumatics?



Two days ago Mesozoic Birds arrived. In the first chapter, p. 7, Witmer
gives the following list (all refs snipped!) of synapomorphies that tie
Archie and "less controversial birds" together:

"In addition to the reflexed hallux, other oft cited synapomorphies include
(1) an elongate prenarial portion of the premaxilla; (2) the breaking down
of the postorbital bar; (3) the absence of dental serrations and the
presence in the teeth of a characteristic constriction; (4) the enlargement
of the cranial cavity; (5) the caudal tympanic recess opening within the
columellar recess; (6) the presence of a caudal maxillary sinus; (7) fewer
tail vertebrae, with the prezygapophyses reduced distally; and (8) various
modifications of the shoulder girdle,  although some of the shoulder
characters may have a broader distribution."

I don't know when this list was compiled; the reflexed hallux may not be
there, (2) is unknown, (3) is wrong, (4) sounds very size-related, (7) is
wrong because of *Microraptor* -- and who knows what the prezygapophyses in
a pygostyle look like? --, and all I can, off the top of my head, think of
for (8) indeed has a broader distribution. (1) deserves consideration --
"enigmosaurs" have it but are too far away to matter in most cladograms,
while *Sinornithosaurus* and dromaeosaurids don't have it, for example. But
why I'm writing this to the list is that I don't know about (5) and (6). I
expect Witmer (who else?) knows what he's writing about here (he also cites
himself for both), but could someone give me a broader picture of where
these characters occur? Many thanks in advance. :-)