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1996 McGUIRE-SYSTEMATICS OF CROTAPHYTID LIZARDS I I
MORPHOLOGY AND CHARACTER DESCRIPTIONS
SKULL ROOF
Prernaxilla (Characters 1, 2; Fig. 2-5, 7).-The
posterodorsally projecting nasal process is long and
very slender in Gatnbelia rvislizenii and G. copei
(Fig. 4, 5) and broad in most Crotaphytus (Fig. 2,
7) and the single specimen of G. coronat. Gambelia
silus (Fig. 3) occasionally has a slender but short
nasal process (seven of 30) owing to its truncated
snout. In C. insularis, the nasal process is also long
and extremely narrow, which may be a consequence
of elongation of the snout region. Some variation
occurs in C. vestigiutn and C. bicinctores, both with
two of 28 specimens having similarly slender nasal
processes, and C. grismeri, with one of five having
a slender nasal process, although not as extreme as
that seen in C. insularis. Among the outgroup taxa,
a narrow nasal process was observed only in Peiro-
saurus tnearnsi and occasional Uta stansburiana,
Dipsosaitrus dorsalis, Phytnaturus pallurna, and Ph.
punae (although the condition observed was not as
extreme as that observed in Gambelia and C. in-
sularis). Therefore, an elongate, narrow nasal pro-
cess is considered to be the derived state.
In Gambelia, the anteromedial portion of the al-
veolar shelf at the articulation of the premaxilla and
vomers is in the form of a strong vertical ridge. This
ridge is rarely present in Crotaphytus (three of 51
C. collaris, one of four C. antiquus). Among the
outgroup taxa, a strong vertical ridge was observed
only in Corytophanes hernandezi, r\.ficroIophw grayi,
two of three Leiocephalus schreibersi, and one of
three Phymattrrus patagorticus zapalensis. There-
fore, a strong vertical ridge at the alveolar shelf is
considered to be the derived state.
The premaxillary base is also subject to much
variation in crotaphytids. In all Gantbelia, plus many
C. antiqiius, C. collaris (primarily those formerly
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Fig. 2.-Doml view ofthc skull ofCroraphyturdickersonae(REE Fig. 3.-Dorsal view of the skull of Garnbelia silw (CAS 22713,
2777, adult male, SVL = 116 mm). Scale = 5 mm. adult male, SVL = 101 mm). Scale - 10 mm.