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BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 32
the rear of the tooth row) and usually well beyond
this point. Juveniles are not always comparable be-
cause their teeth are relatively larger than those of
adults and are often widely spaced. The angular also
extends well beyond the anterior extent of the cor-
onoid in both adults and juveniles. In G. tvislizenii
and G. copei, the angular was never observed to
reach the fourth tooth (from the rear of the tooth
row) and rarely reached beyond the first. In most
specimens, the angular does not extend as far an-
teriorly as does the coronoid. In C. bicincfores, C.
grismeri, and G. silus, the anterior extent of the
angular shows continuous variation with most spec-
imens having an intermediate condition but others
with character states similar to those observed in
G. wislizenii and G. copei or the remaining species
of Crotaphytus. Because of this continuous variation
in these three taxa, 1 have coded each as unknown
for this character. With respect to the outgroup taxa,
the angular projects well anteriorly in chamaeleon-
ids, hoplocercids, the corytophanids Basiliscus bas-
iliscus, B. vittatus, B. plumifom, some Coryto-
phanes cristatus. C. percarinatus, some Laernanctus
longipes, L. serratus, and many polychrotids, while
it is short in tropidurids (except Uranoscodon su-
perciliosus), phrynosomatids, oplurids (except 0.
fierinensis), and iguanids.
The angular bears the posterior mylohyoid fora-
men. This foramen usually is positioned well pos-
terior to the superior apex of the coronoid in Gam-
belia (eight of eight G. copei, 26 of 29 G. silus. 50
of 51 G. wislizenii), while it is equidistant with, or
anterior to, the superior apex in most Crotaphytus
(posterior to the superior apex in two of 49 C. col-
laris, three of 15 C. dickersonae. two of 17 C. ne-
brius, two of 23 C. reficulafus, one of 27 C. vestig-
ium). Although most of the outgroup taxa exhibit
the condition observed in Crotaphyfus, the presence
of the posterior mylohyoid foramen posterior to the
apex of the coronoid in phrynosomatids, some tro-
pidurids, and some polychrotids (Frost and Ether-
idge, 1989) as well as some oplurids prohibits po-
larization of this character.
Coronoid (Character 25; Fig. 13, 14).-The angle
of the posterolingual process of the coronoid is near-
ly vertical in Crotaphytus, while it extends poster-
oventrally at an angle of approximately 45 degrees
in G. tvislizenii, G. copei, and G. corona? (Norell,
1989). Gambelia silus may be intermediate in this
feature or may approach the conditions observed in
Croraphytus or G. tvislizenii-G. copei. Therefore, G.
silus was coded as unknown ("?") for this character.
Most outgroup taxa have a condition similar to Cro-
faphytus (state 0) or occasionally the intermediate
condition usually present in G. silus. The outgroup
taxa with the G. wislizenii-G. copei condition in-
clude only Pefrosaurus mearnsi, Phrynosoma doug-
lassi. P. coronatutn, Uromasfyx. Brookesia sfutnpfi,
and Chamaeleo kersteni (chamaeleonines as a whole
are variable with respect to this feature). Therefore,
the angled posterolingual process of the coronoid
(state 1) is considered to be derived and the vertical
condition ancestral. Norell (1989) considered this
feature to be an unambiguous synapomorphy of
Garnbelia, presumably because he did not examine
specimens of G. silus.
Surangular (Characters 26-28; Fig. 13-1 5). - Im-
mediately anterior to the articular facet lies a me-
dially oriented knob-like process here referred to as
the medial process. A thin shelf of bone may extend
anteriorly between the distal extremity of the medial
process and the body of the surangular (Fig. 15).
This shelf is usually much more strongly developed
in Gambelia and, to a lesser degree, Crotaphyfus
insularis than in the remaining Crotaphytus species.
Crotaphytus vestigium is variable with respect to this
character with seven of 27 having a shelf present.
A lesser amount of variation was observed with a
smaller shelf present in C. bicincfores (one of 25),
C. collaris (five of 50), C. dickersonae (two of 16),
C. nebrius (one of 17), and C. reticulatus (one of
14). In Gambelia, the shelf may entirely fill this
space such that its edge may be either straight or,
more frequently, convex in shape. The strongly de-
veloped condition present in Gambelia suggests that
it may be a further modification or intensification
of the condition observed occasionally in Crofa-
phytus. Thin shelves of bone between the medial
process and the ramus of the mandible are present
in a small number of iguanian taxa, including Lei-
olepis belliana, Oplurus cuvieri, some Brachylophus
fasciatus, some Ufa stansburiana. Urosaurus auri-
culatus, Microlophus grayi, and most Phymarurus
taxa (absent only in P. palluma and some P. punae).
The shelves only approached the condition of Gam-
belia in the four Phymaturus pafagonicus subspe-
cies. This character was coded as a binary character
with the absence of a shelf coded as state 0 and its
presence as state 1 (taxa with intermediate frequen-
cies coded appropriately). The presence of thin
shelves of bone between the medial process of the
surangular and the ramus of the mandible is inter-
preted as the derived state.
An additional process of the surangular may be