Functional morphology of the tongue in the nutcracker (Nucifraga caryocatactes).

The nutcracker Nucifraga caryocatactes belongs to a group of bird species that use their beak and tongue as tools for obtaining food, such as seeds from hard-to-reach cones or nuts from shells. The aim of the present study, carried out with a scanning electron microscope, was to define the morphological features of the tongue of the nutcracker, which seems to be adapted to its environment through specific methods of obtaining food. One of the characteristic features of the nutcracker's tongue is the unique structure of the anterior part of the tongue, which has two long and highly keratinized processes - a product of the renewable keratinized layer of the epithelium covering the ventral surface of the tongue. These dagger-like processes, which are a modified "lingual nail," take a major role in levering up and shelling seeds, which are transported over the short sulcus-shaped body of the tongue. A unique feature of the nutcracker's tongue is the groove separating the body from the root. Two rows of highly keratinized, mechanical, conical papillae are located at the junction of the body and the root. These papillae are mechanically protective elements for passing food particles in the form of seeds. Among lingual glands, only the posterior lingual glands on the root of the tongue have been observed. Their secretion agglutinates dry food before it is swallowed. Results of the present study indicate that the nutcracker's tongue is an efficient tool resembling a lever that is helpful in shelling seeds.