Dental Development and Microstructure

In addition to variation in tooth form and function, lemurs display a wide variety of dental developmental patterns. In fact, lemur dental development often does not "play by the rules" with the quickest pace of tooth formation and eruption sometimes occurring among the largest forms, a pattern which contrasts with the general pattern seen in anthropoid primates (e.g., Godfrey et al., 2005, this volume; Schwartz and Godfrey, 2003; Schwartz et al., 2002). Of note, patterns of dental development appear linked to phylogeny, with extinct, large-bodied relatives of smaller living forms (e.g., Propithecus and Palaeopropithecus) sharing similar patterns of development, despite significant differences in body size (e.g., Godfrey et al., this volume; Schwartz and Godfrey, 2003; Schwartz et al., 2002). Dental development also corresponds to diet and feeding ecology, with noticeable differences between sympatric folivorous and more frugivorous and/or omnivorous lemurs, for example Propithecus v. verreauxi and Lemur catta, in terms of the pace of dental eruption (e.g., Eaglen, 1985; Godfrey et al., 2001, 2004a). In fact, specialized folivores such as Propithecus display early and rapid dental eruption, often possessing a number of erupted deciduous teeth at birth (Eaglen, 1985; Godfrey et al., 2001, 2004a; Schwartz et al., 2002, 2005).

As with morphology and dental development, dental microstructure reflects the feeding ecology of extant (and fossil) lemurs. When compared to anthropoids, lemurs (and extant prosimians in general) possess relatively thin dental enamel (e.g., Godfrey et al., 2005; Martin et al., 2003; Shellis et al., 1998). Because enamel thickness generally corresponds to diet among primates (although not a perfect relationship [e.g., Maas and Dumont, 1999; Martin et al., 2003]), Shellis et al. (1998) argued that, given their thicker enamel, the diet of anthropoids likely consists of a higher proportion of tough foods than does that of prosimians. As seen in Table 2, only highly derived forms such as extant Daubentonia and the large, subfossil Archaeolemur, both of which are quite specialized in their dietary adaptations, possess thick enamel, comparable to well-known hard-object feeders, for example the extant New World capuchins (Cebus) (e.g., Godfrey et al., 2005) and the fossil hominid Paranthropus (e.g., Teaford and Ungar, 2000). Maas (1994) suggested that thin enamel is the primitive condition for lemurs. The rarity of thick-enameled lemurs supports this suggestion.

In addition to enamel thickness, the structure and organization of enamel also reflects dietary adaptations. Along with their thin enamel, extant lemurids exhibit significant enamel decussation (i.e., differentially oriented enamel prisms [Janis and Fortelius, 1988]), with up to 90% of the enamel in Varecia, L. catta, and Eulemur macacao consisting of these prisms (Maas, 1994). Enamel decussation is thought to provide resistance to crack propagation, and often correlates with diets dominated by hard foods (Godfrey et al., 2005; Maas and Dumont, 1999; Martin et al., 2003). Despite the dietary variability exhibited by extant lemurids, the presence of noticeable decussation in this group suggests an adaptation to hard foods

Table 2.

mates

Relative enamel thickness (R.E.T.) of extant lemurs compared with other pri-

Taxona

Mean R.E.Tb

Homo sapiens

Archaeolemur majori\ (extinct)

Varecia variegata\ Lemur catta\ Gorilla gorilla Pan troglodytes Propithecus vemauxi\ Hylobates lar

Paleopropithecus ingens\ (extinct)

Hadropithecusstenognathus\ (extinct) Papio cynocephalus

Homo sapiens

Archaeolemur majori\ (extinct)

Pongo pygmaeus Cebus apella

Pongo pygmaeus Cebus apella

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