Meeting Abstract
Amphibians are unusual among vertebrates in retaining their pharyngeal arch (PA) skeleton as cartilage, developing distinct larval and adult versions of this skeleton in metamorphosing forms, and adapting the adult skeleton for different styles of prey capture. We have proposed that amphibians evolving a metamorphosis was contingent on using cartilage to make and reshape their feeding skeleton. We have also argued that the need for a fully functional feeding skeleton right after metamorphosis requires that the larval skeleton grow with little change in shape. Adult skeletal growth, however, would be expected to vary with the biomechanics of feeding, which differ significantly between tongue protruding and tongue projecting salamanders. Alternatively, if larval growth is not isometric, life history variation could affect both larval and adult skeletal shape in complex ways. This study quantifies and compares the rate of change in shape of the gape and of three PA cartilages (Meckels cartilage, ceratohyal and first ceratobranchial) during larval and/or postmetamorphic growth in eight plethodontids, three ambystomatids, and one dicamptodontid. The plethodontids include six metamorphosing and two direct developing species, and the ambystomatids include two metamorphosing and one paedomorphic species. Gape and cartilage widths and lengths are used to generate allometric equations that are tested for significant differences in the rate of shape change between different elements in the same species, between the same element in different species, and between the same element in the same species at larval and postmetamorphic stages. Species are compared to test for the effects of phylogeny and life history, and to test predictions about the role of cartilage strength and lightness in tongue projection.
