The otic region ofDoleserpeton(Temnospondyli) and its implications for the evolutionary origin of frogs

Abstract

There is increasing evidence that the Palaeozoic temnospondyl amphibians had a frog-like tympanic hearing system. For this reason, the otic region of Doleserpeton is described and compared with modern anurans. The otic capsules are expanded laterally and ventrally relative to other temnospondyls. The opisthotic has a bulbous ventral region resembling the ventrolateral ledge in modern frogs. Two lateral processes are located on the paroccipital process. Comparison with the condition in modern anurans with a tympanic hearing system shows that this may have been the attachment site for the tympanic annulus. Parts of the osseous labyrinth are also described. The inner ear shows numerous features resembling the condition found in frogs. These include strong evidence for the presence of a lissamphibian-type perilymphatic duct most closely resembling that of anurans. This is the first time such a perilymphatic system has been described in any Palaezoic form. The posterior part of the braincase shows a jugular foramen closely associated with the perilymphatic foramen, as in anurans. Although the distribution of these traits among other temnospondyl groups remains little known, the sum of the evidence points to affinities between anurans and temnospondyls, and adds to the evidence for a close relationship between anurans and the Permian amphibamid Doleserpeton. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 738–751.