Re: Some dumb questions

["Mickey Mortimer" <Mickey_Mortimer111@msn.com>]

Jason Michalak wrote-

> Where exactly is the caudal maxillary sinus? Is there a picture/link or
> something you can refer me to so I can see it?

In Hesperornis, it's a fossa on the lateral side of the maxilla (Witmer,
1990).  Specifically, it's on an area that projects dorsally from the medial
part of the main maxillary body, behind the ascending process.  This area is
not ossified in non-avian dinosaurs as far as I can tell.  An oviraptorid
(ZPAL MgD-I/95) has been interpreted as having a homologous fossa on its
interfenestral bar (between the antorbital and maxillary fenestra) by
Elzanowski (1999).  It's possibly homologous, but Hesperornis and other
ornithurines lack interfenestral bars, so this is difficult to test.  Other
non-ornithurines have been described as having caudal maxillary sinuses too.

The fenestrae labeled openings to the caudal maxillary sinus in oviraptorids
(Elzanowski, 1999) seem homologous to the foramina in the lateral wall of
the antorbital fossa of tyrannosaurids (Carr, 1996, 1999), "Alashansaurus"
(Chure, 2001) and perhaps those on the floor in Erlikosaurus (Clark et al.,
1994).  The caudal maxillary sinus in Archaeornithoides (Elzanowski and
Wellnhofer, 1993) on the other hand looks to be homologous to the concavity
between the palatal shelf and lateral wall of the antorbital fossa in
carnosaurs (Madsen, 1974; Currie and Dong, 1993), tyrannosaurids,
Erlikosaurus and Gobipteryx (Chiappe et al., 2001).  A reduced version can
be seen in Velociraptor (Barsbold and Osmolska, 1999) and perhaps the more
dorsal opening in oviraptorids indicated by Elzanowski.  The structures
identified by Witmer (1990) as a wall of the caudal maxillary sinus in
Archaeopteryx were considered palatines by Paul 2002, part of the nasal
septum and an unidentified element by Elzanowski and Wellnhofer 1996, an
unidentified element and possible mesethmoid by Elzanowski 2002, and were
not definitively identified by Elzanowski 2001.  Chiappe (2001) codes
Gobipteryx as having this character, though no mention of it is present in
Chiappe et al. 2001.  Ji et al. (1999) state confuciusornithids lack a
caudal maxillary sinus, though confuciusornithid maxillae are very poorly
preserved.  They are also coded as being absent in carnosaurs, troodontids
and dromaeosaurids by Chiappe (2001).  The ossified medial wall in
Hesperornis seems non-homologous with either structure noted above in
non-avian theropods, though a caudal maxillary sinus could have existed in
the latter.

> Is a caudal tympanic recess that "extends into opisthotic posterodorsal to
> fenestra ovalis, confluent with this fenestra" the same thing as invading
> the columellar recess?

Yes, they're the same condition.  The primitive condition is to have it
penetrate the paroccipital processes at their anterolateral base.

> Is this one of those accessory maxillary/antorbital  fenestra things? Or
are they different?

The posterior/caudal tympanic recess is in the braincase, while the
antorbital and maxillary fenestra are in the maxilla.

Mickey Mortimer