LARSON, P.M.; Ohio University: Morphometric analysis of chondrocranial anatomy and ontogenetic allometry in larval Bufo americanus (Anura: Bufonidae)

Available descriptions of chondrocranial morphology among Bufo tadpoles are inconsistent, the range of variation in chondrocranial structure is not well defined, and no detailed quantitative descriptions of cranial ontogeny currently exist for the genus. This study describes chondrocranial morphology in Bufo americanus based on three samples of tadpoles and reviews chondrocranial morphology in Bufo. Intraspecific variation among samples is also analyzed using geometric morphometric methods in combination with multivariate statistical techniques and ontogenetic allometry is analyzed for sixteen measurements using common principal components analysis. Chondrocranial morphology in Bufo americanus tadpoles is overall similar to that reported for other members of the genus, conflicting only with data provided by Parker (1881) and Sedra (1951). Morphometric analyses indicate that although chondrocranial shape differs consistently among localities, patterns of ontogenetic allometry are conserved among the samples. This indicates that locality specific differences are already present at the earliest stages examined. Ontogenetic analyses indicate a mixture of allometric and isometric scaling, with measurements associated with the palatoquadrate generally scaling with isometry or positive allometry and most remaining measurements scaling with negative allometry. These data provide further evidence that the anuran chondrocranium is not a static structure during pre-metamorphic stages and further indicate that the range of intraspecific variation in larval anuran morphology may be greater than previously thought.