The morphology of the external and the middle ear (auditory ossicles) in Chlamyphorus truncatus is influenced by its fossorial life. The external auditory canal consists of three parts. The most distal part is a short (cartilaginous) auricle which reaches anteriorly close behind the eye. Posteriorly to the auricle is a long, thin bony duct which consists of two segments, movable against each other. This tube leads through a narrow porus into the third part of the canal, the recessus meatus, which is enclosed in the bulla. The recessus with the narrow porus is characteristic for many fossorials and has a morphology with physical characteristics of a resonator (Helmholtz). The malleus and the stapes in Ch. truncatus are also influenced by fossorial life. Based on the dorsal view of the malleus head, the Xenarthra can be divided into two groups. To the first division belong the Dasypodidae with the Chlamyphorinae and Dasypodinae, to the second the Myrmecophagidae and Bradypodidae. The malleus of Cyclopes, a myrme-cophagid, differs from that in the other Myrmecophaginae and is similar to the malleus in the Dasypodinae. Two kinds of experiments should be undertaken: (a) physiologic-acoustic experiments in a fossorial to determine the effect of the recessus and (b) acoustic experiments varying the dimensions and positions of a tube and a porus leading into a resonator.

Keywords:
Functional morphology, External auditory canal, Ossicles, Fossorial
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© 1976 S. Karger AG, Basel
1976
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