ИСТИНА

Our morphofunctional study of the feeding apparatus (both – jaw and hyoid) of the frugivorous broadbills Calyptomena - a genus of small archaic group Eurylaimides (suboscine passerines of the Old World) - revealed a number of peculiar features, interpreted here as adaptations for the frugivorous diet. For example, Calyptomena broadbills have morphological features that prevent passive protraction of the upper jaw when the bird tears off an attached fruit. These birds can successfully consume fruits that differ significantly in both size and hardness, including very large ones with a big seed, comparable with the bird head in size. Calyptomena broadbills swallow all the fruits entirely since the construction of their small and gracile but very wide bill does not allow any significant mechanical processing of the object before swallowing. The branches of their lower jaw are arranged as wide as possible for this skull structure, but when the bird swallows the fruit, they are able to move apart passively, further expanding the gap. This movement may activate a special mechanism for locking of the jaw joint. This mechanism provides a peculiar force action of the jaws to the object, which allows them to increase the force pushing the fruit down the throat with jerks. Active retraction of the Calyptomena tongue also helps pushing the fruit down the throat. These birds can mash soft fruits and squeeze the nourishing juice from them, pressing the fruit in a wide tongue to the specifically fortified arch of the oral cavity. Their movable tongue also helps to perform complex manipulations in the bill with relatively small objects. Some of these specific details and mechanisms are reported in other fruit-eating birds (for example, hornbills, Asian barbets, mousebirds, etc.), but only in Calyptomena all of them are present within one feeding apparatus.