The Lower Permian amphibamid Doleserpeton (Temnospondyli: Dissorophoidea), the interrelationships of amphibamids, and the origin of modern amphibians

ABSTRACT

The Lower Permian amphibamid Doleserpeton annectens (Temnospondyli) is of great importance to our understanding of the origin of modern amphibians. Here, we describe this taxon in detail. The pedicellate bicuspid dentition of Doleserpeton is more similar to that of modern amphibians than any other Palaeozoic form, including Gerobatrachus. The dermal bones of the skull are almost completely smooth, unlike other dissorophoids. The braincase and parts of the postcranial skeleton are more highly ossified than in other amphibamids, and Doleserpeton is unlikely to represent a juvenile stage. The ribs are relatively short and posteriorly curved, as in many modern amphibians, but unlike most lepospondyls. The palate shares numerous features with modern amphibians, including the configuration of the interpterygoid vacuities and the structure of the vomers. We propose that the closest sister taxon to Amphibamidae is Dissorophidae (armored dissorophoids) and that the trematopids are more basally situated than has been suggested by some studies. Micropholis is probably not basal to the other amphibamids, and the clade support for a monophyletic Amphibamidae is surprisingly weak unless Dissorophidae and branchiosaurs are included in this taxon. Doleserpeton adds to the strong evidence for a temnospondyl origin of batrachians, particularly for anurans, and the hypothesis proposing a lepospondyl origin of modern amphibians is therefore questioned. Doleserpeton also shares numerous features with Eocaecilia, pointing to a monophyletic origin of lissamphibians from amphibamid temnospondyls.

ACKNOWLEDGMENTS

We thank Robert L. Carroll, David M. Green, and Hans C. E. Larsson (McGill University, Montreal) for helpful comments, technical advice, and specimens. Special thanks also go to Jason Anderson (University of Calgary) and Farish A. Jenkins and Bill Amaral (Museum of Comparative Zoology, Harvard) for providing additional help and specimens.