Mammal Teeth: Origin, Evolution, and Diversity

Euarchontoglires

13 Euarchontoglires Most mammalian species can be distinguished by the nature of the cusps of a single molar tooth. —r. l. carroll, 1988 EUARCHONTOGLIRES IS THE MOST speciose of the supraordinal mammalian clades, comprising about 60% of all recent mammalian species (see, e.g., Rydell and Yalden 1997; Nowak 1999; Y.-F. Lee and McCracken 2002; D. E. Wilson and Reeder 2005; Debelica, Matthews, and Ammerman 2006; and Zanon and Reis 2007). These species are found in habitats ranging from desert to rainforest, from sea level to high altitudes, and from the Arctic to the equator to the Subantarctic. While the adaptive diversity of Euarchontoglires does not approach that of the other boreoeutherian supraorder, Laurasiatheria, the radiation is still remarkable in many ways. Some euarchontoglirans are fossorial; others are semiaquatic, terrestrial , or arboreal. Their locomotor adaptations allow them to burrow, creep, walk, run, swim, climb, swing, and glide. The range of their body weight is also impressive , spanning five orders of magnitude, from about 2.5 g to about 275 kg. Euarchontoglirans also vary in food preferences and diet. Most species are principally or wholly herbivorous. Some are adaptable opportunists, whereas others are dietary specialists, consuming only a few species or plant part types. Some include insects, other invertebrates, and small vertebrates in their diet, and a few specialize on these things. This dietary diversity is reflected in variation in dental form and in other adaptations. This chapter presents a family-by-family survey and basic descriptions of dental forms in recent euarchontogliran orders. Euarchontoglires combines Euarchonta, which includes the orders Scandentia, Dermoptera, and Primates (i.e., “Archonta” without Chiroptera), with the traditional Glires, or Myochonta (the orders Lagomorpha and Rodentia) (see chapter 5). D. E. Wilson and Reeder’s (2005) classificatory scheme is followed here unless otherwise noted. Scandentia Early classifications included the tree shrews in “Insectivora”; however, many subsequent researchers put them in “Archonta” or even within Primates (McKenna 1975; Szalay 1977; Novacek 1992a, 1992b; McKenna and Bell 1997; Sargis 2004; Symonds 2005; see also chapter 5). Molecular studies today place Scandentia at the root of crown Euarchontoglires, the sister taxon to all of its other orders (see Horner et al. 2007). These conservative, squirrel-like forms can be divided into two families, Ptilocercidae and Tupaiidae. ptilocercidae (fig. 13.1). There is only one recent species in the family Ptilocercidae, Ptilocercus lowii. Molecular evidence suggests that this species is the e u a r c h o n t o g l i r e s 189 the P2 or the P4 , and the latter is large and somewhat molarized (Gregory 1910; Lyon 1915; Steele 1973; P. W. Butler 1980; Yates 1984; Emmons 2000). Ptilocercus molar morphology is conservative and has been considered a reasonable model for tooth form of the primitive primate, if not the primitive placental mammal (Gregory 1910; P. W. Butler 1980; Han, Sheldon, and Stuebing 2000). The upper molars are more or less dilambdodont, though the classic W-shaped ectoloph does not have much of a central apex given the lack of a mesostyle. The buccal edge of each molar forms a continuous cingulum. The first two upper molars have a small but distinct hypocone on the posterolingual edge. The M3 is truncated posteriorly, with a reduced metacone and no hypocone. The lower-molar trigonids and talonids are subequal in length, though the anterior cusps are slightly higher than the posterior ones. The three trigonid cusps form an equilateral triangle and are connected by a V-shaped crest. The molars bear distinct hypoconulids. The last lower molar is slightly narrower than the first two. The occlusal crests are not well developed, and the cusps are generally lower and blunter in Ptilocercus than in other scandentians (Gregory 1910; Lyon 1915; Steele 1973; P. W. Butler 1980; Yates 1984; Emmons 2000). sister taxon to other scandentians. The pen-tailed tree shrew is found in Southeast Asia, mostly in the canopies of primary and secondary forests. Adults weigh about 25–60 g. These mammals are largely insectivorous and prey on a variety of insects and other small invertebrates as well as some small vertebrates. Ptilocercus is also noted for recent reports of the consumption of fermented, alcohol-rich nectar, which has little to do with their teeth but is nonetheless interesting (Lim 1967; E. Gould 1978; Stone 1995; Nowak 1999; Emmons 2000; L. E. Olson, Sargis, and Martin 2004; F. Wiens et al. 2008). The pen-tailed tree shrew’s dental formula is I 2/3, C...