a Note that A13C determinations for Hadropithecusstenognathus (-8.4 to -13.2) suggest a diet richer in C4 and/or CAM plants (or in animals consuming these plants) than in any other subfossil lemur. For comparative purposes (see Peters and Vogel, 2005), we note that A13C values for specialized grazers, including Theropithecus, generally range from ~ +1 to -4. Paranthropus robustus and Australopithecus africanus have stable carbon isotope values ranging from--6 to -11 (thus overlapping Hadropithecus).
phism (Jenkins and Albrecht, 1991; Kappeler, 1991, 1996). Nevertheless, low sexual dimorphism, by itself, does not generate female dominance.
In displaying low levels of sexual dimorphism and widespread female dominance, extant lemurs differ from anthropoids. Among anthropoids, polygyny is common, and the degree of canine and body size dimorphism is correlated largely with the degree of contest competition among males for mates (Plavcan, 2001). Except in cases where females form coalitions capable of challenging males, anthropoids generally display male social dominance coupled with moderate to high levels of sexual dimorphism. In short, anthropoids conform to the basic predictions of sexual selection theory—polygynous species tend to exhibit greater degrees of sexual dimorphism in canine height and in body size, and males dominate females in agonistic encounters. Relative canine size is also correlated with agonism.
The lack of dimorphism in extant lemurs has been related to selective forces affecting male and female reproductive strategies (e.g., Fietz, 1999 a,b; Kappeler, 1991; Kraus et al., 1999; Lawler et al., 2005). Monogamy is common among lemurs (especially among nocturnal species), but others exhibit promiscuity with scramble competition, suppression of sexual function in subordinate individuals, or forms of male-male contest competition that avoid direct combat. Levels of social agonism appear to be correlated with relative canine height (the relationship of canine height to other measures of size, such as molar length) (Godfrey et al., 2002; Plavcan et al., 1995). In some species (e.g., Lemur catta), both males and females have long, trenchant upper canines (and both sexes tend to exhibit high agonism), whereas in others (e.g., Indri indri), both sexes have low-crowned canines (and tend to exhibit low agonism).
Extinct lemurs resemble extant lemurs in showing little or no skull length or canine height dimorphism and in showing tremendous interspecific variation in the height of the canine relative to measures of body size (Godfrey et al., 1993, 2002). The virtual absence of canine or skull length dimorphism among giant lemurs confirms a lack of convergence to the size-correlated anthropoid pattern (Smith and Cheverud, 2002). Male social dominance, with strong intrasexual combat competition for mates, seems unlikely. Nothing contravenes the possibility of female dominance in giant lemurs. Furthermore, if agonism for both sexes is correlated with relative maxillary canine height, then certain extinct lemurs (especially Megaladapis) likely exhibited agonism on a par with diurnal lemurs such as L. catta and other lemurids, while others had lower levels of agonism (Table 3). It is noteworthy that the canines of extinct lemurs are generally not nearly as long and daggerlike as those of male cercopithecines.
Were extinct lemurs energy conservers?
Several lines of evidence suggest that the answer is affirmative, especially for some of the largest subfossil species. All extant strepsirhines studied to date, including Malagasy cheirogaleids, lepilemurids, lemurids, and indriids, have basal or resting metabolic rates (BMRs) well below Kleiber's line and reduced in comparison to most size-matched anthropoid primates (Genoud, 2002; Ross, 1992; Schmid and Ganzhorn, 1996). Based on this phylogenetic effect alone, we suspect that the giant lemurs were also comparatively hypometabolic, and it seems reasonable to extend this inference from BMR to FMR (field metabolic rate; Nagy, 1987) and MMR (maximal metabolic rate; Weibel et al., 2004). Although daily torpor adds to the energy conservation of very small lemurs during the cooler dry season (Schmid et al., 2000), we doubt that this extreme metabolic strategy was practiced by the large extinct species. Nevertheless, long periods of inactivity
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