For snakes, maximum gape size can determine the size and shape of consumable prey. Small body size may accentuate the limitations of gape; however, some evidence indicates that juvenile snakes may compensate for small body size by exhibiting negative gape allometry. In this study, we tested the hypothesis that Red-bellied Mudsnakes (Farancia abacura) display negative allometry for relative gape size. We measured five external head dimensions for each of 10 specimens and directly measured maximum gape circumference using either a ring or bracelet mandrel. Soft tissue was removed from each skull, after which we measured nine osteological features of the cranium. Maximum gape circumference exhibited negative allometry with snout–vent length, as did all cranial dimensions except quadrate length, which was isometric. All cranial bones exhibited positive allometry with skull length except for parietal width, which was isometric with skull length. Based upon a model of the external characteristics using Akaike Information Criterion, jaw length and head width were the strongest predictors of gape circumference. Supratemporal length, skull length, and mandible length were the three highest ranked osteological dimensions for predicting maximum gape. These model ranks differ from those of similar studies conducted using different snake species, indicating that the morphological determinants of gape circumference may be highly diverse among lineages.

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