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