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, 7 (1), 11963

Bite Force in the Horned Frog (Ceratophrys Cranwelli) With Implications for Extinct Giant Frogs

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Bite Force in the Horned Frog (Ceratophrys Cranwelli) With Implications for Extinct Giant Frogs

A Kristopher Lappin et al. Sci Rep.

Abstract

Of the nearly 6,800 extant frog species, most have weak jaws that play only a minor role in prey capture. South American horned frogs (Ceratophrys) are a notable exception. Aggressive and able to consume vertebrates their own size, these "hopping heads" use a vice-like grip of their jaws to restrain and immobilize prey. Using a longitudinal experimental design, we quantified the ontogenetic profile of bite-force performance in post-metamorphic Ceratophrys cranwelli. Regression slopes indicate positive allometric scaling of bite force with reference to head and body size, results that concur with scaling patterns across a diversity of taxa, including fish and amniotes (lizards, tuatara, turtles, crocodylians, rodents). Our recovered scaling relationship suggests that exceptionally large individuals of a congener (C. aurita) and extinct giant frogs (Beelzebufo ampinga, Late Cretaceous of Madagascar) probably could bite with forces of 500 to 2200 N, comparable to medium to large-sized mammalian carnivores.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
An individual Ceratophrys cranwelli biting a force transducer. Leather strips glued to ends of bite bars provide a natural surface that encourages high-effort biting and avoids damage to teeth and bones. The strips also indicate a bite point for standardization of bite-force performance (see Methods).
Figure 2
Figure 2
Head width vs. bite force for specimens of Ceratophrys cranwelli. (a) Plot of bite force on head width in which each point represents maximum bite force of three trials (standardized here for bite position at posterior teeth, see Methods) measured during an experimental session with each specimen represented by a different symbol (n = 8). The line represents a power function fitted to the pooled data (y = 0.0004x2.9608, R2 = 0.9209). (b) Log-log plot in which each point represents maximum bite force (standardized here for bite position at jaw tips, see Methods) measured during an experimental session with each specimen represented by a different symbol (n = 8). Thin linear regression lines are given for each specimen. The thick dotted regression line was calculated from the pooled data (slope = 3.3269). Estimated bite forces for Beelzebufo were calculated using reduced major axis regression (see Methods).
Figure 3
Figure 3
Relationship between head width and size of palatal conduits of major jaw-adductor musculature of ceratophryid frogs. Log-log plot of head width vs. average area of right and left palatal conduits of the major jaw-adductor musculature of Ceratophrys spp. based on dissections and skeletal specimens. Solid linear regression line represents all Ceratophrys spp. (open squares □, y = 2.4902x − 2.4094, R2 = 0.9524). Dotted linear regression line represents only C. cranwelli (filled squares ■, y = 2.0263x − 1.6627, R2 = 0.8784). Estimate for the exceptional C. aurita specimen (LACM 163430) is represented by a triangle (△). Three estimates for the Beelzebufo composite reconstruction with a head width of 111 mm (Fig. 3D in ref.) are represented by diamonds (◊), based on conservative, likely, and maximum conduit size. Silhouettes scaled to the same head width, from smallest to largest, are provided for C. cranwelli (collection of A.K.L.), C. ornata (UMCZ R1529), C. ornata (LDUCZ W186), C. aurita, and the Beelzebufo reconstruction. Scale bars = 40 mm. Note that our estimate of maximum bite force for Beelzebufo is based on larger individuals with a head width of 154 mm (estimate of maximum size provided in ref. based on recovered material).
Figure 4
Figure 4
Teeth of Ceratophrys cranwelli. As with almost all other extant frogs bearing teeth, Ceratophrys has teeth only on the upper jaw. Unusual among frogs, the teeth of Ceratophrys exhibit a derived non-pedicellate morphology and have sharp recurved tips situated upon robust, labiolingually expanded bases. (a) view of teeth with jaws closed; (b) view of teeth with mouth slightly open; (c) close-up of single tooth. Scale bars = 1 mm.

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