Geometric morphometric of the R. mexicanus species complex.
No skull views showed sexual dimorphism in shape (dorsal: F = 1.18,p = 0.28; ventral: F = 1.09, p = 0.36) or CS (dorsal: t =
0.25, p = 0.80; ventral: t = 0.93, p = 0.35). For the
dorsal view of the skull, there was no significant correlation between
CS and shape (F = 0.70; p = 0.55). For the ventral view, the
CS-shape correlation was significant (F = 8.39; p = 0.001), with
CS explaining only 9.10 % of the shape variation hence the allometric
effect was considered relatively weak.
Significant differences were found between the cranial shape (dorsal: F
= 3.41, p = 0.004; ventral: F = 8.92, p = 0.001) of the
delimited species. For the dorsal view, pairwise comparisons showed
significant differences among all putative species (Fig. 5). The mean
shape of R. mexicanus clade IIIB differed from R.
mexicanus clade IIA in having a relatively longer nasal bone (landmarks
1 and 2), a slightly narrower interorbital region (landmark 5), and the
braincase with a tendency to narrow towards the caudal region of the
occipital bone. When compared to R. mexicanus clade I, theR. mexicanus clade IIIB showed a narrowing of the anterior-medial
region of the skull (landmarks 1-8; 35) although the braincase is
slightly wider towards the ends of the parietal-interparietal bones.R. mexicanus clade IIA and R. mexicanus clade I differed
in most of the landmarks that characterized the skull shape, having the
latter a longer rostrum and a braincase that was wider towards the
parietal-interparietal region but narrower towards the curvature of the
occipital bone.
In the ventral shape, only the comparison between R. mexicanusclade IIA and R. mexicanus clade IIIB did not differ
significantly in skull shape. Differences in the mean shape betweenR. mexicanus clade IIIB and R. mexicanus clade I occurred
in the anterior region of the skull; R. mexicanus clade I had a
longer incisive foramen, but a shorter palate. The R. mexicanusclade I skull shape showed a notable contraction of the landmarks 22-24,
which describe the foramen magnum, with respect to the other putative
species. Also, R. mexicanus clade I differed from R.
mexicanus clade IIA in that the former had a shorter line of molars and
slightly wider basicranium towards the posterior region of the zygomatic
bar, but with a tendency to narrow towards the tympanic bullae. No view
showed significant skull size differences (CS) between delimited species
(dorsal: F = 2.19; p = 0.12; ventral: F = 1.72; p = 0.18).
The CVA showed a partial overlap in the morphospace of all putative
species for the dorsal view and considerable discrimination of R.
mexicanus clade I for the ventral view along the positive CV1 axis
(Fig. 5). The LDA based on skull shape did not assign 100% of the
individuals to the corresponding delimited species (Table 3). The dorsal
side had a lower correct discrimination rate (65%) than the ventral
side (77%). In both views, most of the misclassed individuals belonged
to R. mexicanus clade IIIB, while the best classification
accuracy was in R. mexicanus clade I, with a majority of
individuals correctly assigned.