Ontogeny and evolutionary morphology of the skeleton in frogs

Ontogenetic studies, or studies of development, have repeatedly proven insightful in exploring questions of morphological evolution. Here, two projects illuminate the relationship between ontogeny and the evolution of skeletal morphology in frogs. In the first part of this dissertation, I examine the evolution of skull development in pipoid frogs, a group that is exceptional in both morphology and life history. Two methods are used. First, skull bone ossification sequences are examined within a phylogenetic context. Second, studies are made of ontogenetic shape change in the skull using thin-plate spline morphometrics. Important differences between pipoid skull development and that of other frogs are uncovered. These include the convergent evolution of primitive ossification patterns still retained in extant salamanders, and the elaboration of novel trajectories of ontogenetic shape change which create the unusual pipoid morphology. The second part of this dissertation examines the phenomenon of miniaturization in frogs. Because miniaturization has evolved numerous times in frogs and has reached impressive extremes, frogs make an ideal group in which to study the effects of miniaturization on morphological evolution. I use qualitative presence/absence characters in the skull and limbs, as well as shape variables from thin-plate spline morphometrics to identify patterns of morphological change which are statistically associated with the evolution of miniaturization. These statistically significant patterns are discussed in the context of functional constraints and paedomorphosis.