Origin and Function of the Toothcomb

The original function of the toothcomb has been a matter of some debate for many years (e.g., Avis, 1961; Stein, 1936). Depending on the study, the toothcomb

Figure 2. Six-toothed mandibular toothcomb in Lemur catta (USNM 395517) (photo by Frank Cuozzo).

originally functioned as a grooming tool (Rosenberger and Strasser, 1985; Szalay and Seligsohn, 1977), for food procurement (Martin, 1972), or one or both of these scenarios, though there is insufficient evidence to support either hypothesis unequivocally (Asher, 1998; Rose et al., 1981). Martin (1972) argues that the grooming function of the toothcomb is secondary to its tooth-scraping role. The addition of the canine demonstrates that the scraping role of the structure took precedence over the normal piercing role of the canine. In contrast, Szalay and Seligsohn (1977) posit that the inclusion of the canine in the six-toothed comb does not increase the cutting surface of the comb, forming instead an additional interdental space. The resulting comb was used for fur grooming. The more transversely compressed comb of the exudate-feeding Phaner and the robust four-toothed indriid structure (Figure 3) are interpreted as derived. Rosenberger and Strasser (1985) suggest that the toothcomb is part of an olfactory complex that follows the reduction of the upper incisors away from a feeding function, which allows a connection of the philtrum with the vomeronasal organ through the resulting interincisal diastema. The toothcomb functions to stimulate and distribute

Figure 3. Four-toothed mandibular toothcomb in Propithecus diadema (USNM 63349) (photo by Frank Cuozzo).
Figure 4. Lingual view of the single anterior tooth (white arrow) in Daubentonia mada-gascariensis (USNM 199694) (photo by Frank Cuozzo).

olfactory secretions throughout the body and brings secretions up to the vomeronasal organ. Whatever its original function, the incisiform canine represents an unusual addition to the toothcomb, especially since the anterior premolar subsequently became caniniform in many taxa (Martin, 1972; Swindler, 2002; Tattersall, 1982).

Among extant lemurs, the toothcomb is used as both a grooming and a feeding tool (e.g., Richard, 1978; Sauther et al., 2002). In addition to numerous field accounts of such usage, Rose et al. (1981) demonstrated via SEM that the interstitial facet of the central incisor had grooves and scratches consistent with hair grooming, and Asher (1998) found that the interincisal gap is wider in gregarious taxa, which presumably groom socially. In indriids, Daubentonia, and Phaner, the toothcomb has a more derived adult morphology, which is probably related to its use in food procurement in these taxa. Food ingestion in L. catta and P. v. verreauxi takes place both anteriorly in the mouth and on the postcanines, depending on the size of the fruit or leaf (Yamashita, 2003). Initial food placement is related to food size more than to a material property such as toughness, as seen in the processing of large tamarind fruit (Tamarindus indica) by L. catta (Cuozzo and Sauther, 2006, in press).

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