On the “otic element” in Amphibia Salientia

1 An examination of one hundred and fifty‐six species, representing ten families, shows that the otic element does not persist as a separate bone in the adult anuran skull. 2 Developmental studies in thirty‐six species from eleven families show that the element is diagnostic of and restricted to the Bufonidae and the Atelopodidae. In every case the bone originates over the dorso‐lateral edge of the crista parotica and subsequently fuses with the squamosal. This supra‐otic position is retained throughout life in the Bufonidae but in the Atelopodidae, the element rotates postero‐laterally until it lies along the outer edge of the auditory capsule. 3 In all the Bufonidae and Atelopodidae the depressor mandibulae muscle consists of a single, thick band originating supra‐otically in the former family and latero‐otically in the latter. These conditions are found in no species from any other family. Developmental studies in all bufonid and atelopodid species examined, show that the otic element provides the base from which the depressor muscle originates and it is proposed that the presence of the element and this condition of the muscle are linked characters. 4 On the evidence of fossil forms, temporal myology and the compound nature of the fronto‐parietal, the otic element is homologized with a supratemporal. 5 From the distribution of the supratemporal bone and its associated condition of the depressor muscle it is concluded that (a) the families Leptodactylidae and Bufonidae should be reinstated, (b) full family status should be accorded to the Dendrobatinae and the Atelopodinae, (c) a close relationship exists between the Bufonidae and the Atelopodidae and the former should be regarded as the ancestral stock, (d) the genus Cacophryne should be regarded as an independent derivative of the arciferal Pedostibes stock, (e) Nectophryne should be returned to the Bufonidae. These conclusions are supported by an examination of the shoulder girdle of Cacophryne and by an investigation into the organ of Bidder.