Memoir cover 0.tif - Ohio University College of Osteopathic Medicine

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