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WITMER-ANTORBITAL CAVITY OF ARCHOSAURS 33
FIGURE 21. Scaphognathus crassirostris. Drawings of rostral part of
skull in A, left lateral and B, ventral views. (Modified after Wellnhofer,
1991b.)
single median "nasal process" (e.g., Pterodactylus kochi, Wellnhofer,
1968; Germanodactylus cristatus, Wellnhofer, 1978; Anhanguera
santanae, Wellnhofer, 1987; Pteranodon longiceps,
Bennett, 1991). This structure probably marks the boundary
between the narial and antorbital cavities.
The only "rhamphorhynchoid" in which the antorbital cavity
excavates any significant antorbital fossa is Eudimorphodon
ranzii (Wild, 1978), in which the jugal ("lacrimal" of Wild,
1978) bears a shallow rostral fossa. Jugal antorbital fossae are
present in the pterodactyloids Pteranodon longiceps (KUVP
976, USNM 13868; see also Witmer, 1987b; Bennett, 1991, in
press) and perhaps Santanadactylus araripensis (Wellnhofer,
1985). Lacrimal antorbital fossae are present in Pteranodon longiceps
(KUVP 976, USNM 13868; Witmer, 1987b; Bennett,
1991, in press), Anhanguera santanae (AMNH 25555), and
probably Tapejara wellnhoferi (Wellnhofer and Kellner, 1991)
and Tropeognathus mesembrinus (Wellnhofer, 1987). Despite
extensive transformation of palatal conformation (Wellnhofer,
1978), the antorbital cavity in all Pterosauria opens medially
into the nasal cavity, directly opposite the choana (Fig. 21). The
course of the nasolacrimal canal is rarely discernible, although
Wellnhofer (1985) described an orbital aperture of the canal in
Araripesaurus santanae, which, by its position, indicates a
probable course dorsomedial to the antorbital cavity. Accessory
cavities are developed in many, if not all, of the large pterodactyloids
(see below).
Crurotarsi: Parasuchia-The taxonomic allocation of individual
parasuchian specimens remains in a state of flux, as
do the phylogenetic relationships of the taxa (see Doyle and
Sues, 1995). This paper primarily uses the names employed by
Ballew (1989) andlor the holding museums, with the attributions
made in Long and Murry's (1995) important monograph,
when different, indicated in brackets; not all taxa are demonstrably
monophyletic. In general in parasuchians, the antorbital
cavity is within the maxilla and lacrimal with varying contributions
from the jugal and nasal (Fig. 22D). In basal parasuchians
(Ballew, 1989), such as Parasuchus hislopi [Paleorhinus
sp.] (Chatterjee, 1978a), Paleorhinus bransoni (FMNH UC
632), Paleorhinus scurriensis [Paleorhinus bransoni] (TTUP
8090), and Angistorhinus grandis (FMNH UC 631), there is a
well-developed antorbital fossa rimming the caudal, dorsal, and
rostral margins of the internal antorbital fenestra, extending
onto the jugal, lacrimal, nasal, and maxilla; the ventral edge of
the external fenestra, however, is formed by the sharp edge of
the supralveolar lamina of the maxilla. In most higher parasuchians
there is usually little or no external antorbital fossa (e.g.,
Rutiodon lithodendrorum [Leptosuchus crosbiensis], UCMP
27181, Fig. 22D; Rutiodon [Leptosuchus] adamanensis, UCMP
26699; Pseudopalatus pristinus, AMNH 7222, UCMP 34249,
27281, NMMNH P-4256; Mystriosuchus planirostris, AMNH
10644). In all known parasuchians, the antorbital cavity opens
medially into the nasal cavity just opposite the choana where it
is floored by the palatine and usually the maxilla. In Phytosaurus
sp. (BMNH 38037) and Pseudopalatus pristinus (NMMNH
P-4256), the nasolacrimal canal passes between the lacrimal and
prefrontal; to reach the choana, the duct would have had to pass
dorsomedially over the antorbital cavity (it should be noted that
Camp [I9301 placed the canal within the lacrimal bone, but this
could not be confirmed on the specimens cited by him). Parasuchians
thus display the specified osteological correlates.
Crurotarsi: Ornithosuchidae-Ornithosuchidae have a
large internal antorbital fenestra bounded by the maxilla, lacrimal,
and jugal (Fig. 10). In both Ornithosuchus longidens
(BMNH R2409, R3143; see also Walker, 1964) and Riojasuchus
tenuisceps (Bonaparte, 1972) the internal fenestra communicates
medially with the nasal cavity and its rostral third is
directly opposite the choana. The antorbital cavity is partly
floored medially by the palatine, as mentioned earlier. Laterally,
the antorbital cavity excavates an extensive antorbital fossa on
the maxilla, lacrimal, and jugal around the entire margin of the
internal fenestra, except for a small section caudally where the
lacrimal overhangs the cavity (Fig. IOA). The antorbital fossa
is more extensive in R. tenuisceps (Bonaparte, 1972) than in 0.
longidens. There are two alternative courses for the nasolacrima1
canal in 0. longidens (the canal is unknown or undescribed
in R. tenuisceps). In the first alternative, the canal would pass
through the lacrimal bone such that the duct would open laterally
into the region of the lacrimal antorbital fossa (much as
in theropods). Walker (1964) cited as evidence an apparent caudal
foramen within an isolated lacrimal of 0. longidens (BMNH
R3143, a cast from a natural mold), which he interpreted as the
orbital aperture of the canal. However, in an actual bony specimen
(BMNH R3142), this putative foramen is clearly absent.
In the second alternative, the nasolacrimal duct would pass between
the lacrimal and prefrontal bones. The orbital aperture of
the nasolacrimal canal appears to be represented by a notch
between the lacrimal and prefrontal (BMNH R3142, R3143);
the canal then passed rostrally as a rostrally widening groove
within the suture (BMNH R3143; Walker, 1964: fig. 3b). The
latter alternative is probably more likely, but in either case, the
nasolacrimal duct would assume a course dorsomedial to the
antorbital cavity. In the latter interpretation, the deep caudodorsal
lacrimal fossa could well be an "incipient pneumatic
cavity" as described by Walker (1964:104). Ornithosuchids
thus display all the osteological correlates of a pneumatic antorbital
cavity.
Crurotarsi: Non-crocodylomorph Suchia-In most noncrocodylomorph
suchians, the internal antorbital fenestra is
moderately large (very large in Gracilisuchus stipanicicorum;
Romer, 1972), invariably opening toward the nasal cavity directly
opposite the choana, usually in the rostral half of the
fenestra (see Figs. 9, 23). The fenestra is bordered by the maxilla,
lacrimal, and sometimes part of the jugal. In most cases,
the palatine partly floors the medial portion of the antorbital
cavity. The internal fenestra is surrounded, usually on all sides,