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46 SOCIETY OF VERTEBRATE PALEONTOLOGY, MEMOIR 3
ing into chambers within the nasal bone. As noted previously,
these nasal recesses appear to be associated with the excavatio
pneumatica in the maxillary ascending ramus. Currie and Zhao
(1994a) noted that the two cavities of S. dongi are extensive
but do not communicate. Monolophosaurus jiangi (Zhao and
Currie, 1994) deserves special mention in that its nasal bones
form a large hollow crest with two large apertures caudally that
actually pass from one side to the other, establishing a contralateral
communication between the antorbital cavities, as well
as invading the body of the nasal; furthermore, two additional,
more rostral, foramina pneumatize the nasal bone and then continue
rostrally to pneumatize the premaxillae. Nasal pneumatic
recesses have not been described for other theropods (except
for oviraptorosaurs; see below), and they can be shown to be
positively absent in Tyrannosauridae, Ornithomimosauria, Troodontidae,
Erlikosaurus andrewsi (PST 10011 11; Clark et al.,
1994), and Archaeopteryx lithographica (cast of Eichstatt specimen).
As with the lacrimal and jugal recesses, nasal recesses
are described in Deinonychus antirrhopus (YPM 5210, 5232;
MOR 747) here for the first time (see also Witmer, 199%; Witmer
and Maxwell, 1996). Ostrom (1969:19) described a
"groove with three moderate-sized, oval foramina" within the
nasal of D. antirrhopus but had "no explanation for this pattern."
Comparison with other theropods (as well as further
preparation) reveal that Ostrom's groove is the nasal antorbital
fossa and the "oval foramina" are pneumatic foramina leading
into small cavities.
Palatine recesses are found in some theropods and typically
are cavities or foramina in the dorsal surface of the palatine
bone that are clearly associated with the antorbital cavity. These
are absent in Ceratosauria and some large tetanurans such as
Allosaurus fragilis. Where present, they invariably are caudal
or caudolateral to the choana, just medial to the contact with
the maxilla, and rostrolateral to the presumed pterygoideus fossa,
if present. In Archaeopteryx sp. (cast of Solenhofer Aktien-
Verein specimen; see also Elzanowski and Wellnhofer, 1996),
the dromaeosaurids Deinonychus antirrhopus (YPM 5210,
5232; Fig. 32) and Velociraptor mongoliensis (cast of PIN
314318; Osm6lska, 1985), and the troodontid Saurornithoides
mongoliensis (AMNH 6516), there is a well-developed fossa in
this position, and, in at least D. antirrhopus, this fossa leads
into a small cavity. In Sinraptor dongi, the fossa surrounds a
moderately large foramen that leads into a cavity within the
choanal process (Currie and Zhao, 1994a). Tyrannosaurids have
often large foramina in the dorsal surface of the palatine that
lead into a strutted cavity with the bone (Molnar, 1991; Carr,
1996). There may be just a single large foramen leading into
the bone (e.g., Daspletosaurus torosus, CMN 8506; Tyrannosaurus
rex, AMNH 5027) or sometimes two or more (e.g., Nanotyrannus
lancensis, Gilmore, 1946; Albertosaurus sarcophagus,
CMN 5601; Tarbosaurus bataar, Maleev, 1974). Few theropod
taxa can be scored for palatine recesses, and thus the
phylogenetic distribution of these features is problematic. If it
were not for the clear presence of palatine recesses in Sinraptor
dongi, it might have been possible to regard them as a synapomorphy
of at least Maniraptora (assuming Holtz's [I9941
placement of Tyrannosauridae is correct) if not Coelurosauria.
A discussion of the facial structure of theropods would not
be complete without special mention of the peculiar Mongolian
oviraptorosaurs (Barsbold et al., 1990). Oviraptor philoceratops
and its relatives clearly manifest the osteological correlates permitting
the inference of an antorbital air sac. Furthermore, their
facial skeletons have been described as being extensively pneumatic
by virtually all recent workers (Osmblska, 1976; Barsbold,
1983; Barsbold et al., 1990). In fact, the facial bones in
some species are developed into a tall, cassowary-like crest
formed by a fine lattice of bony trabeculae (Barsbold et al.,
1990). Oviraptorosaurs were not discussed much in the above
analysis of theropod accessory cavities because their skulls are
so transformed that it is not always easy to identify homologous
pneumatic structures. Virtually all of the facial elements have
complex cavities within them. The ones in the maxilla, lacrimal,
and nasal are associated with the antorbital cavity (Osm6lska,
1976), whereas the cavities within the premaxilla and others in
the nasal and even the frontal bone are apparently connected
with the nasal vestibule (Barsbold et al., 1990).
Coelophysis bauri also merits further discussion in that it
lacks all of the cavities and chambers in the facial bones, thus
strongly resembling many non-dinosaurian archosaurs; yet it is
regarded as a derived member of its clade, Ceratosauria (Rowe
and Gauthier, 1990; Holtz, 1994). Since more basal ceratosaurians
such as Ceratosaurus nasicornis and Dilophosaurus wetherilli
are large-skulled forms manifesting some~of these cavities
(and, presumably, pneumatic diverticula of an antorbital air
sac), it is reasonable to suggest that C. bauri also possessed a
large paranasal air sinus, but, by virtue of small skull size, did
not develop pneumatic diverticula into its facial bones. Therefore,
some aspects of facial pneumaticity may have a size-related
(i.e., allometric) component.
Sauropodomorpha-In the prosauropod Plateosaurus engelhardti
(AMNH 6810), the nasal bone sends a lamina lateral
to the maxillolacrimal contact that broadly overhangs the antorbital
cavity (Fig. 12A). In fact, there is large, dorsal, C-shaped
(laterally open) hiatus framed by the laminae of the maxilla
and lacrimal that the nasal caps (Fig. 12D). That portion of the
nasal roofing the aperture has a deeply excavated recess (Fig.
12C), and may be the closest approach among sauropodomorphs
to a theropod-like bony accessory cavity. It is not
known how widely this nasal recess is distributed among prosauropods,
but since the nasal overhangs the antorbital cavity
in Sellosaurus gracilis (Galton, 1985b) and perhaps Massospondylus
carinatus (Gow et al., 1990), the recess also may be
present in these forms.
Ornithischia-The palatine of Lesothosaurus diagnosticus
has two well-marked fossae on its dorsolateral surface. The caudal
fossa was interpreted earlier as a muscular fossa. The rostral
fossa (Fig. 7C, D), however, appears to be associated with the
antorbital cavity and may well be a pneumatic fossa. It resembles
in some respects the palatine fossa noted above for the
small theropods Deinonychus antirrhopus (Fig. 32) and Velociraptor
mongoliensis.
Haubold (1990) described a deep rostral extension of the antorbital
cavity within the maxilla of the basal thyreophoran
Emausaurus ernsti (Fig. 18), which could be an accessory cavity.
Similarly, in another basal thyreophoran, Scelidosaurus harrisonii,
there is a moderately large foramen at the rostral apex
of the maxillary antorbital fossa that could lead to an accessory
cavity, but it is unknown whether it expands into a chamber
within the bone.
Clearer evidence of accessory cavities is available for protoceratopsians
(Fig. 20C, D). In at least Bagaceratops rozhdestvenskyi
and Protoceratops andrewsi, an accessory cavity is
associated with the maxillary antorbital fossa (Maryanska and
Osm6lska, 1975; Osm6lska, 1986). This "intramaxillary sinus"
enters the bone via a slit or cleft (sometimes two slits as in
AMNH 6466) within the floor of the maxillary recess. It subsequently
expands, forming a cavity running the length of the
maxilla dorsal to the tooth roots (Osm6lska, 1986; Fig. 20C,
D). It is not known whether it occurs in other protoceratopsians,
but Sternberg (1951:232) regarded the antorbital fossa (his
"maxillary sinus") as being "much deeper" in Leptoceratops
gracilis than in P. andrewsi, perhaps suggesting the presence
of an accessory sinus in this form as well.
Pterosauria-Many large pterodactyloids have spaces that
can be interpreted as accessory cavities. For example, in Pteranodon
longiceps (KUVP 976, USNM 13868), there is a clear