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WITMER-ANTORBITAL CAVITY OF ARCHOSAURS 37<br />
I \<br />
sulc max<br />
fen antorb<br />
int<br />
Lg<br />
wall cav paraias ch<br />
FIGURE 26. Pelagosaurus typus. A, drawing <strong>of</strong> antorbital region <strong>of</strong><br />
BMNH 32599 in left lateral view. B, schematic drawing <strong>of</strong> a medial<br />
view <strong>of</strong> the right antorbital region <strong>of</strong> the same specimen (observed<br />
through the orbit directly and with dental mirror).<br />
pter<br />
FIGURE 25. Protosuchian crocodylomorphs. A, Protosuchus richardsoni,<br />
snout <strong>of</strong> MCZ 6727 (with some details modified from Crompton<br />
and Smith [I9801 and Sues et al. [1994]) in left lateral view. B,C,<br />
Gobiosuchus kielanae, snout in (B) left lateral and (C) ventral views.<br />
(B,C modified after Osmolska, 1972.)<br />
1962). Metriorhynchids have a small internal antorbital fenestra,<br />
bounded by the maxilla and lacrimal and <strong>of</strong>ten the nasal,<br />
but usually have a much more extensive antorbital fossa (Fig.<br />
27). Whereas the external antorbital fenestra is <strong>of</strong>ten continued<br />
rostrally as a narrow groove in P. typus and some teleosaurids<br />
(Fig. 26A), there is always a broad antorbital fossa in metrio-<br />
rhynchids (bounded by the maxilla and lacrimal and usually<br />
also the nasal and jugal), excavated into the side <strong>of</strong> the snout<br />
rostral to the fenestra and continued rostrally as a tapering<br />
groove on the maxilla (Fig. 27; Wenz, 1968; Gasparini and<br />
Chong Diaz, 1977; Buffetaut, 1982). There is considerable intras~ecific<br />
variation in the form <strong>of</strong> the fossa and groove. For<br />
example, in Metriorhynchus superciliosus, the boundary between<br />
fossa and groove may be relatively subtle (BMNH<br />
R3014, R3900, R4762), or the fossa may be very deeply excavated<br />
and extensive with the rostral groove being distinct<br />
from (although continuous with) the rostral edge <strong>of</strong> the fossa<br />
(BMNH R3899). Also in this species and in Teleidosaurus<br />
gaudryi (BMNH R3353), the antorbital fossa clearly extends<br />
caudally onto the lacrimal (BMNH R3900, R4762; see Fig. 27).<br />
The relationship between the primary choana and internal<br />
antorbital fenestra is known in P. typus (BMNH R32599) and<br />
M. superciliosus (BMNH R2048; see also Wenz, 1968) where<br />
the fenestra clearly opens medially into the nasal cavity and is<br />
directly opposite the primary choana. An unequivocal nasolacrimal<br />
canal could not be located in even the well-preserved<br />
material <strong>of</strong> P. typus, Steneosaurus spp., and M. superciliosus;<br />
the only possible candidate is a matrix-filled pit within the orbital<br />
margin <strong>of</strong> the lacrimal in Teleidosaurus gaudryi (BMNH