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Caecilians, or Gymnophiona, constitute one of the three extant orders of the Recent Amphibia and comprise about 170 named species in six families. They are the least known, major living tetrapod clade. Compared to frogs and salamanders, caecilians have an unusual skull morphology. With few exceptions, previous studies on caecilian morphology have been restricted to investigations on adult material and were usually carried out on small samples. This thesis investigates skull development in caecilians. Earlier reports of an unusually high number of individual skull ossifications in Hypogeophis rostratus are addressed and found to be erroneous. Changes in skull morphology and myology at metamorphoses are investigated in representatives of all taxa possessing free-living larvae. It is argued that caecilians are derived from gymno- or zygokrotaphic ancestors and that stegokrotaphy evolved within Recent caecilians. To investigate the influence of different life-histories, postembryonic skull development was studied in two direct-developing species. The direct-developing Boulengerula taitanus is characterized by very immature hatchlings, which is correlated with an extended period of post-hatching parental care in this species, during which juveniles feed on the modified stratum corneum of their mothers. Direct development in caecilians is characterized by ontogenetic repatterning and heterochronic shifts in certain developmental events. The ontogeny of Scolecomorphus kirkii was studied as a representative of a viviparous form. The emerging picture of available published information, together with observations presented here, suggest a previously unsuspected degree of developmental diversity among caecilians. It is further argued that caecilians are lissamphibians with temnospondyl affinities rather than closely related to lepospondyl microsaurs.

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