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NUMBER 89 315
which is unlike that in any theropod. Theropod teeth were once
strongly believed not to vary with age (Currie et al., 1990), but
this belief has been refuted by the discovery of subcorneal, unserrated
teeth in dromaeosaurid hatchlings (Norell et al., 1994).
Similar teeth are present in Archaeomithoides and may have
been present in the early juveniles of troodontids.
MAXILLA.—The maxilla has broad palatal shelves that meet
at, or at least approach, the midline in the Therizinosauroidea,
Oviraptoridae, Caenagnathidae, Omithomimosauria, Archaeomithoides,
Hesperomis, and the paleognaths except Struthio.
A fairly broad palatal shelf of the maxilla was probably present
in Gobipteryx. Unfortunately, contrary to previous interpretations,
the palatal aspect of the maxilla (as well as premaxilla)
remains entirely unknown in Archaeopteryx.
In Hesperomis each palatal shelf of the maxilla ends with
two processes, the lateral and the medial palatine process. The
medial process, known as the maxillopalatine, is the only portion
of the palatal shelf that remains in Struthio and the neognaths.
The peg-like process of the oviraptorids and caenagnathids
corresponds in position to the maxillopalatine of
neomithine birds in being a caudomedial extension of the palatal
shelf that contacts the vomer.
At least in the oviraptorosaurs, Archaeomithoides, and birds,
the maxillary shelf provides a floor for the caudal maxillary sinus.
Other theropods are believed to have only the rostral sinus
(Witmer, 1990). Among Mesozoic birds, the caudal maxillary
sinus is well documented in Hesperomis (Witmer, 1990) and
may have been present in Archaeopteryx, although the evidence
of its presence in the fifth skeleton provided by Witmer
(1990:360, fig. 14) is probably incorrect (Elzanowski and
Wellnhofer, 1995). The upper jaw of the fifth skeleton, however,
contains a vertical, median or paramedian element (Elzanowski
and Wellnhofer, 1995, fig. 7X) that is similar in shape
and location to the medial wall of the caudal sinus in the oviraptorids.
PALATINE.—The palatine of the omithomimosaurs, therizinosauroids,
oviraptorids, caenagnathids (Sues, 1997, fig. 2),
and birds has a maxillary process that is much longer than the
rostromedial vomeral process and overlaps the maxillary palatal
shelf ventrally. In the neomithines, including Hesperomis,
the maxillary process is known as the premaxillary process because
it extends even further rostrally and reaches the premaxilla.
The palatine has a broad pterygoid (caudal) wing that overlaps
the pterygoid ventrally in the therizinosauroids,
oviraptorids, birds, and probably in caenagnathids.
In the omithomimosaurs, the palatine has a dorsal, transversely
oriented process situated close to the lacrimal (Osmolska
et al., 1972:116, 136). A prominent transverse crest is
present in Archaeopteryx in a comparable location (Elzanowski
and Wellnhofer, 1996:89, fig. 9A), and three transverse
crests are present in Chirostenotes (Sues, 1997, fig. 2). In contrast,
the dorsal process of the palatine that ascends to the lacrimal
in the oviraptorids is oriented in the parasagittal plane
(Figure 2B).
PTERYGOPALATINE FENESTRA.—Gauthier (1986) used the
pterygopalatine (subsidiary palatine) fenestra as one of two diagnostic
cranial characters of the newly defined Coelurosauria,
although it is known to be present in only two of the originally
included families, the omithomimosaurs and dromaeosaurids.
The pterygopalatine fenestra has been subsequently identified
in Archaeomithoides, the therizinosauroids, and tentatively in
Chirostenotes and Gobipteryx. This fenestra is lacking in the
oviraptorids (Figure 1). In Hesperomis and other neomithines
there is no separate fenestra, although the situation in Gobipteryx
suggests that it may have merged with the choana. The
lack of an appropriate embayment in either the palatine or
pterygoid of Archaeopteryx suggests either the absence of this
fenestra or a configuration similar to that in the neomithines.
The uncertain status of the pterygopalatine fenestra in birds
makes it of little use in the search for avian relatives.
ECTOPTERYGOID AND POSTPALATINE FENESTRA.—The ectopterygoid
is situated rostrally and, as a result, the postpalatine
(palatine) fenestra is reduced in the oviraptorids (Figures 1, 2)
and therizinosauroids (although it is unclear whether the fenestra
is present in the latter). The fenestra is much smaller in Gallimimus
(Osmolska et al., 1972:108) than it is in the dromaeosaurids
and may be even smaller, if present at all, in
Omithomimus edmontonicus Sternberg (ROM 851), where the
ectopterygoid is preserved in contact with the lacrimal (pers.
obs.) in a position very different from that reconstructed in
Gallimimus. In the oviraptorids and Erlikosaurus, the ectopterygoid
is lateral to the palatine, which is due to its rostral
position and the presence of the pterygoid wing of the palatine.
This also may be tme of the Caenagnathidae (Sues, 1997:701).
Although the ectopterygoid is positioned caudally in the fifth
specimen of Archaeopteryx, it may have overlapped, at least in
part, the long pterygoid wing of the palatine.
The oviraptorid ectopterygoid differs from that of Archaeopteryx
and from other theropods, including the therizinosauroids,
in the lack of the jugal hook, its distal articulation primarily
with the lacrimal and maxilla rather than the jugal, and its
strongly slanting position between the lacrimal and the palatine
(Figure 2). In all these differences, the oviraptorid ectopterygoid
agrees with the avian uncinate (uncinatum=lacrimopalatinum),
which in the neomithine birds articulates with the caudoventral
margin of the lacrimal and descends caudoventrally
to the palate (Figure 3). Although in modem birds the uncinate
tapers toward the ventral tip and either articulates with the palatine
or ends free above it, in oviraptorids the bone flares out
ventrally and articulates with both the palatine and the pterygoid.
This difference may be accounted for by the reduction of
the rostral part of the pterygoid (which became separated and
reduced as the hemipterygoid) in the neomithine birds. In Hesperomis
the uncinate probably approached or marginally contacted
the large hemipterygoid (Elzanowski, 1991, fig. 3). The
uncinate of extant birds is clearly a vestigial structure that is
extremely variable in shape.
The uncinate is widespread among the neomithines. It has
been found in the Stmthionidae and Rheidae among the paleog-