The auditory region of Brachycephalus and its bearing on the monophyly of the genus (Anura: Brachycephalidae)

Abstract

We surveyed the morphology of the auditory region of members of the anuran genus Brachycephalus. The sample included seven of the eleven known species; in addition, Brachycephalus ephippium and B. vertebralis were each represented by several specimens from different localities. All species lack a tympanum, tympanic annulus, stapes, and Eustachian tube. However, the operculum and the m. opercularis remain. The large operculum bears a robust process for the m. opercularis and covers most of the fenestra ovalis. The auditory apparatus of Brachycephalus is distinguished by the large size and the orientation of the fenestra ovalis, which faces posterior, rather than lateral. The morphology of these structures is compared to those of other minute brachycephalid frogs considered to be close relatives of Brachycephalus, and the importance of these characters as evidence of the monophyly of the genus is discussed. We also discuss the importance of other morphological features cited to support close relationships among small-sized brachycephalids, and consider the role of miniaturization in generating convergent pattern of loss of morphological features.