Memoir cover 0.tif - Ohio University College of Osteopathic Medicine
Memoir cover 0.tif - Ohio University College of Osteopathic Medicine
Memoir cover 0.tif - Ohio University College of Osteopathic Medicine
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
WITMERANTORBITAL CAVITY OF ARCHOSAURS 45<br />
antrum and fenestra are innovations <strong>of</strong> Tetanurae or Neotetanurae,<br />
but new dis<strong>cover</strong>ies could easily change this conclusion.<br />
Clearly there has been a fair amount <strong>of</strong> homoplasy, especially<br />
among the earlier lineages; this variation becomes, in effect,<br />
sorted out in Coelurosauria in which the maxillary recesses are<br />
fairly consistent. Despite the phylogenetic ambiguities, the<br />
point emerging from this discussion is that the complicated and<br />
variable nature <strong>of</strong> the maxillary recesses <strong>of</strong> theropods are indeed<br />
compelling morphological evidence for the presence <strong>of</strong><br />
paranasal air sinuses.<br />
Paul's (1988a) compromise solution to the function <strong>of</strong> the<br />
antorbital cavity is pertinent at this point. He suggested that the<br />
dorsal pterygoideus muscle attached to the margin <strong>of</strong> the internal<br />
antorbital fenestra and that the surrounding antorbital fossa<br />
lodged paranasal air sinuses; the epithelial diverticulum would<br />
have traversed the maxillary fenestra to pass from the nasal<br />
cavity to the antorbital cavity. Notwithstanding the problems<br />
detailed earlier regarding the muscular hypothesis, Paul's hypothesis<br />
fails in that it cannot apply to all archosaurs or even<br />
to all theropods because maxillary fenestrae are limited perhaps<br />
to just a single clade, thus leaving the fossae <strong>of</strong> other archosaurs<br />
unkxplained. Furthermore, with regard to theropods, it reverses<br />
the direction <strong>of</strong> ~neumatization. Although - the maxillarv sinuses<br />
<strong>of</strong> some theropods (e.g., Allosaurus fragilis) have medial apertures,<br />
the following taxa can be shown to have no internal<br />
fenestrae, demonstrating that the subsidiary diverticula must<br />
have entered the accessory cavities (passing through the promaxillary<br />
and/or maxillary fenestrae) from the external side <strong>of</strong><br />
the maxilla, not the internal side: PiatnitzkysaurusJoresi (Bonaparte,<br />
1986), Megalosaurus hesperis (BMNH R332), Afrovenator<br />
abakensis (UC OBA I), Ornitholestes hermanni<br />
(AMNH 619), Marshosaurus bicentesimus (UUVP 4695,<br />
1846), and perhaps Deinonychus antirrhopus (YPM 5232).<br />
Thus, Paul's (1988a) compromise is not applicable even for<br />
these theropods.<br />
The lacrimal recess is another accessory cavity associated<br />
with the antorbital cavity. In many theropods (especially large<br />
forms), the lacrimal has a large recess expanding within the<br />
caudodorsal portion (body) <strong>of</strong> the bone that opens rostrolaterally<br />
into the antorbital cavity (Fig. 29A). In most cases, the<br />
opening <strong>of</strong> the cavity is a single, rather broad aperture located<br />
in the rostroventrolateral surface <strong>of</strong> the body <strong>of</strong> the bone, and<br />
is continuous with the smooth surfaces <strong>of</strong> the lacrimal antorbital<br />
fossa. Examples include Ceratosaurus nasicornis (USNM<br />
4733, Afrovenator abakensis (UC OBA 1; Sereno et al., 1994),<br />
Allosaurus fragilis (UUVP 2133, YPM-PU 14554, Fig. 29A),<br />
and Yangchuanosaurus shangyuensis (Dong et al., 1983),<br />
among others. In Tyrannosaurus rex (AMNH 5027, CM 9401,<br />
others), this single aperture is restricted to a relatively small,<br />
more discrete foramen. In a number <strong>of</strong> taxa, additional openings<br />
may be present rostral to the main aperture: e.g., Acrocanthosaurus<br />
atokensis (Stovall and Langston, 1950), Giganotosaurus<br />
carolinii (Coria and Salgado, 1995), some individuals <strong>of</strong> Allosaurus<br />
fragilis (e.g., UUVP 5814, BYU 5125), Sinraptor dongi<br />
(Cume and Zhao, 1994a), and Daspletosaurus torosus (CMN<br />
8506). A number <strong>of</strong> taxa lack any lateral apertures into the body<br />
<strong>of</strong> the lacrimal bone, although they may retain moderately deep<br />
lacrimal antorbital fossae; examples include Coelophysis bauri<br />
(CM 31374; Fig. 14), Dilophosaurus wetherilli (UCMP 77270),<br />
abelisaurids (Novas, 1992), Torvosaurus tanneri (Britt, 1991),<br />
Monolophosaurus jiangi (Zhao and Cume, 1994), Troodon formosus<br />
(RTMP 82.19.23; Cume, 1985; Witmer, 1990), Dromiceiomimus<br />
brevitertius (CMN 12228), Utahraptor ostrommaysi<br />
(Kirkland et al., 1993), Archaeopteryx lithographica (BMNH<br />
37001; Fig. 16B), and Erlikosaurus andrewsi (PST 100/111;<br />
see also Clark et al., 1994). Given the absence <strong>of</strong> such openings<br />
in most small maniraptorans it is probably significant that Deinonychus<br />
antirrhopus (YPM 5232; MOR 747; see also Witmer<br />
and Maxwell, 1996) shows the more-or-less typical condition<br />
<strong>of</strong> more basal tetanurans, a moderately large aperture; furthermore,<br />
as in some <strong>of</strong> the other theropods noted above, there is<br />
an additional, smaller foramen just rostral to the main opening.<br />
Sereno et al. (1994, 1996) listed "lacrimal pneumatic excavation"<br />
as a synapomorphy <strong>of</strong> their Tetanurae, and this seems<br />
reasonable although the lacrimal recess <strong>of</strong> Ceratosaurus nasicornis<br />
is well within tetanuran variation (Witmer, 1995~).<br />
Holtz's (1994) analysis definitely showed a lot <strong>of</strong> homoplasy in<br />
this feature, and, in fact, he probably significantly underestimated<br />
the amount <strong>of</strong> homoplasy (e.g., the dis<strong>cover</strong>y <strong>of</strong> lacrimal<br />
pneumatic recesses in D. antirrhopus noted above; see also Witmer,<br />
1995~).<br />
These lacrimal pneumatic apertures lead into cavities <strong>of</strong> variable<br />
size, such that the body and cornual process (if present, as<br />
in Ceratosaurus nasicornis and Allosaurus fragilis) is hollow.<br />
The internal architecture <strong>of</strong> the lacrimal recess can be assessed<br />
for only a few taxa. For example, in one specimen <strong>of</strong> A. fragilis<br />
(UUVP 2133), the lacrimal recess has three cavities partly subdivided<br />
by internal ridges; the recess does not extend far into<br />
either the rostral or ventral rami. Molnar (1991) also identified<br />
three cavities within the lacrimal <strong>of</strong> Tyrannosaurus rex, and the<br />
recess extends far into the rostral ramus in one specimen (CM<br />
9401). In Albertosaurus sarcophagus (CMN 5601, RTMP<br />
86.114.1; see also Carr, 1996), the cavity within the rostral ramus<br />
opens laterally within the antorbital cavity via a foramen.<br />
The ventral ramus <strong>of</strong> the lacrimal usually has no evident cavities,<br />
although it appears to be hollow in one tyrannosaurid specimen<br />
(RTMP 83.30. I).<br />
Jugal recesses are found in a number <strong>of</strong> theropods, and, in<br />
most cases, take the form <strong>of</strong> a slit-like or occasionally round<br />
foramen at the caudoventral apex <strong>of</strong> the jugal antorbital fossa.<br />
Such a foramen is found in all tyrannosaurids and has been<br />
regarded as a synapomorphy <strong>of</strong> that group (Bakker et al., 1988;<br />
Molnar et al., 1990; Molnar, 1991). The distribution <strong>of</strong> this<br />
feature, however, is more complicated. It is fairly certain that<br />
ceratosaurians and at least some basal tetanurans (Bakker et al.,<br />
1992) lack jugal recesses. Sereno et al. (1994, 1996) regarded<br />
a "jugal pneumatic excavation" as a synapomorphy <strong>of</strong> Tetanurae,<br />
and deep jugal antorbital fossae with pneumatic foramina<br />
similar to tyrannosaurids are found in Monolophosaurus jiangi<br />
(Zhao and Currie, 1994), Afrovenator abakensis (UC OBA 1;<br />
Sereno et al., 1994), Sinraptor dongi (Curie and Zhao, 1994a),<br />
some individuals <strong>of</strong> Allosaurus fragilis (Currie and Zhao,<br />
1994a), Acrocanthosaurus atokensis (Stovall and Langston,<br />
1950), and Carcharodontosaurus saharicus (Sereno et al.,<br />
1996). Most coelurosaurs (other than tyrannosaurids), however,<br />
appear to lack jugal recesses; this seems to be the case for<br />
Omitholestes hermanni (AMNH 619), oviraptorosaurs, troodontids,<br />
and ornithomimosaurs, although additional preparation<br />
(and the proper search image) could change this assessment.<br />
For example, further preparation <strong>of</strong> specimens <strong>of</strong> Deinonychus<br />
antirrhopus (YPM 5210, 5232; MOR 747; Maxwell and Witmer,<br />
1996) reveals a well developed jugal pneumatic recess.<br />
The internal structure <strong>of</strong> the jugal recess is known for few taxa,<br />
but, in Sinraptor dongi (Currie and Zhao, 1994a) and Tyrannosaurus<br />
rex (Molnar, 1973, 1991), the pneumatic foramen<br />
leads into a series <strong>of</strong> cavities within the m&illary and postorbital<br />
rarni <strong>of</strong> the jugal.<br />
Nasal recesses, foramina, and cavities within the nasal bones<br />
associated with the nasal antorbital fossa, are not common.<br />
They are absent in ceratosaurians, although Gilmore (1920:82)<br />
identified "a number <strong>of</strong> pneumatic cavities" in the nasal <strong>of</strong><br />
Ceratosaurus nasicornis. Allosaurus fragilis (UUVP 3839,<br />
BYU 5124, USNM 4734, YPM-PU 14554; Fig. 29A), Sinraptor<br />
dongi (Cume and Zhao, 1994a), Yangchuanosaurus shangyouensis<br />
(Dong et al., 1983), and Carcharodontosaurus saharicus<br />
(Sereno et al., 1996) exhibit one to three foramina lead-