One fruitful approach to animal function has been to investigate the 'unusual' members of a lineage, species that appear to deviate from the typical form, exhibit novel functions or superlative performance, or inhabit extreme environments. This research approach has contributed to the understanding of the form and function of such amazing structures and behaviors as chameleon tongue projection (Schwenk and Bell, 1988;Wainwright et al., 1991;de Groot and van Leeuwen, 2004), tongue protrusion in plethodontid salamanders (Lombard and Wake, 1976Deban and Marks, 2002), water running in basilisk lizards (Laerm, 1973(Laerm, , 1974Hsieh, 2003), wall climbing in geckos (Russell, 1975;Irschick et al., 1996), extreme jaw protrusion in fishes (Liem, 1979;Westneat and Wainwright, 1989;Westneat, 1991), brain-warming muscles in billfish (Block et al., 1993), and 'flying' in fishes (Fish, 1990;Davenport, 1992), frogs (Emerson and Koehl, 1990) and lizards (Hairston, 1957). Conceptually, these studies explore the limits to biomechanical and behavioral evolution, provide informative and appealing examples of adaptive change, and expand knowledge of functional biodiversity.Catoprion mento (Cuvier), the wimple piranha, has a strange diet and equally unusual anatomy and feeding behavior.Catoprion is a monotypic genus of small South American characin that inhabits clear freshwater streams and lakes with abundant submerged vegetation (Taphorn, 1992). Its specific name, 'mento', is Greek for 'chin', referring to the distinctive protuberance created by the curve in its banana-shaped, elongate lower jaw (Fig.·1). Its reduced, conical-shaped teeth on the upper jaw project forward when the jaws are closed (Gery, 1977;Sazima, 1983;Taphorn, 1992). The dietary breadth of Catoprion mento is one of the narrowest reported for fishes; scales form an important proportion of the diet throughout most of ontogeny, and adults feed almost entirely on this prey (Vieira and Gery, 1979;Sazima, 1983;Nico and Taphorn, 1988). Despite our perception that scales should be an unappetizing meal, lepidophagy is relatively widespread in fishes, having evolved independently in at least five freshwater and seven marine families (Sazima, 1983). Although the functional morphology of scale feeding has not previously been experimentally investigated, anatomical and behavioral observations suggest that a diversity of morphologies and attack behaviors are used by lepidophagous predators (Roberts, 1970;Major, 1973;Liem and Stewart, 1976; Whitfield, 1979;Sazima, 1977Sazima, , 1983 Winemiller, 1997, 1998) and that the behavioral origins of scale feeding may be different for different lineages (DeMartini and Coyer, 1981;Sazima, 1983;Sazima and Machado, 1990).Surprisingly, scales are a relatively nutritious food source. In addition to layers of keratin and enamel, teleost scales contain a dermal portion and are covered, in life, with a protein-rich mucus layer (van Oosten, 1957;Wessler and Werner, 1957;Harris and Hunt, 1973;Gorlick, 1980;Whitear, 1986). They are a rich source...