The skeletomuscular systems of the feeding apparatus of the Noisy Scrub-bird, Atrichornis clamosus (Passeriformes: Atrichornithidae)
Abstract
The cranial osteology and the jaw and tongue musculature of Atrichornis clamosus are described. Noteworthy are the large, free lacrymal and the distinct dorsal hump or ridge on the basal portion of the maxillary culmen. Aside from the lacrymal, little strong support exists in the cranial osteology for the generally accepted relationship between Atrichornis and Menura. The considerable differences in skull morphology between these genera are not surprising because of the much larger skull of Menura, about three times that of Atrichornis in linear measurements. Other than the large, free lacrymal, the skulls of the Menurae differ markedly from those of the bowerbirds, arguing against a close affinity between these two groups. The jaw muscles provide no useful information, at this time, on the possible evolutionary history and the affinities of Atrichornis, but the tongue musculature does yield some interesting clues. One feature, partial insertion of the M. trachohyoideus on the ceratobranchiale, is relatively primitive, but one aspect of the hyoid skeleton, lateral flattening of the basihyale, and five features of the tongue musculature are advanced. Most interesting are the vestigial nature of the M. stylohyoideus, a condition otherwise known only in woodpeckers and some meliphagids, and the complete insertion of the M. hypoglossus anterior on the anterior tip of the basihyale, seen also in Dicaeum, Oedistoma, Promerops and a few other passerine birds. These features of the tongue musculature suggest strongly that Atrichornis is not primitive among the oscines, but do not, as yet, provide a clear idea of its relationships.
