Comparative morphology of the primate tongue.

To clarify the role of the primate tongue as a means to better understand the evolution of oral function among primates - an example of adaptation within the restricted phylogenetic group - we review the morphological knowledge of the tongues of extant primates in relation to phylogenetic classification. Prosimians tongues are more effective than those of Haplorhini for taking up food with the tongue alone, because they are capable of fine movement when outside the oral cavity. However, the role of the tongue in food uptake has diminished when juxtaposed with progress in hand manipulation of food and tools in Haplorhini, especially with the manipulation of tools by Homininae. This change in the tongue from prosimians to Homininae can be regarded as degeneration in food uptake by the tongue, although the functional role of the tongue within the oral cavity has not diminished. The distribution pattern and form of lingual papillae, except foliate papillae, are very similar among all reported primates species. Although foliate papillae are generally well developed in Haplorhini, most prosimian species have no foliate papillae, or a different type of papillae that substitute for foliate papillae. There are three vallate papillae in prosimian species and the New-World macaques, Platyrrhini. These papillae exhibit an inverted V-shape and are more numerous in Old World macaques, Catarrhini. These differences seem to be the result of phylogenetic origin.