The stapes of Edops craigi and ear evolution in the lissamphibian stem group

The Lower Permian temnospondyl Edops craigi exemplifies an early and plesiomorphic condition of the single ear ossicle or stapes among the temnospondyls, the probable stem group of lissamphibians. In Edops, the 11-cm-long bone is more massive than in other temnospondyls, has a distinct neck, a dorsal crest and incompletely subdivided footplate and ventral process. Despite a range of invariances, temnospondyl stapes were much more diverse than previously conceived. A survey of described stapes gives insight into character evolution of the ear ossicle in the lissamphibian stem group. These include alternative patterns of paedomorphosis, proportional size change, morphology of tympanic region and reorientation of the auditory apparatus.