Sexual dimorphism in Xenodon neuwiedii skull revealed by geometric morphometrics (Serpentes; Dipsadidae)

Sexual dimorphism in snake head/skull is poorly known, although analyses in other vertebrate groups have already pointed this kind of morphological difference. Herein we evaluated the existence of sexual dimorphism in the skull of Xenodon neuwiedii through Geometric Morphometrics (GM). We found that females have larger skulls than males using centroid size data. Considering the ventral view of the palatomaxillary apparatus, compared to females, males tend to have longer maxilla, ectopterygoid slightly laterally shifted, palatine slightly shorter, and longer pterygoid. For the dorsal view, males showed larger snout, more oblique frontoparietal suture, posterior region of the skull more tapered, larger supraoccipital, and larger and more oblique supratemporals. Xenodon neuwiedii showed static allometry only for the symmetric component of the dorsal view, with 9.7% of shape variation explained by size. The present study is the first evaluating and describing sexual dimorphism in skull shape for snakes independently of size. We compared our results with other studies and concluded that to accurately perform intraspecific analyses or to better understand sexual and/or natural selection, sexual dimorphism should be considered, even for structures (e.g. skull) that are traditionally not used for this purpose.