Peter Larson: Chondrocranial development in larval Rana sylvatica (Anura: Ranidae): A morphometric analysis of cranial allometry and ontogenetic shape change

This study provides baseline quantitative data on the morphological development of the chondrocranium in a larval anuran. Both linear and geometric morphometric methods are used to quantitatively analyze size related shape change in a complete developmental series (n = 73) of larvae of the wood frog, Rana sylvatica. The null hypothesis of isometry was rejected in all geometric morphometric and most linear morphometric analyses. Reduced major axis regressions of 11 linear chondrocranial measurements on size indicate a mixture of allometric and isometric scaling. Measurements in the otic and oral regions tend to scale with negative allometry and those associated with the palatoquadrate and muscular process scale with isometry or positive allometry. Geometric morphometric analyses, based on a set of 11 chondrocranial landmarks, include linear regression of relative warp scores and multivariate regression of partial warp scores and uniform components on log centroid size. Results indicate that body size explains about one quarter to one third of the total shape variation found in the sample. Areas of regional shape transformation (e.g., otic region, trabecular horns) are identified by thin-plate spline deformation grids and are concordant with linear morphometric results. These results indicate that the anuran chondrocranium is not a static structure during the pre-metamorphic stage with allometric patterns generally following scaling predictions for tetrapod cranial development.