Discussion And Conclusions

This chapter summarizes some of our inferences to date regarding the behavior and ecology of extinct lemurs. We now ask how those inferences affect our perception of the ecospace occupied by past and present lemur communities? Do they offer support for either of the competing explanations of unusual living-lemur traits?

First, we know that the hard-object processing guild was larger in the past than it is today. The only remaining member of this guild is Daubentonia madagas-cariensis, whereas in the past it was occupied by several widespread archaeole-murid species as well as at least two species of Daubentonia. Looking particularly at Archaeolemur spp., we see postcranial adaptations reminiscent of cercop-ithecines, signalling greater commitment to ground locomotion than in other lemurs. We now know that these species also displayed: (1) molars with thick enamel and unusually heavy enamel prism decussation; (2) relatively high encephalization; (3) relatively slow dental development, with delayed weaning and a protracted period for acquisition of adult foraging skills; (4) a diverse diet, probably including difficult-to-extract food resources; and (5) a relatively high total energy budget (inferred from enlarged semicircular canals). Interestingly, Daubentonia madagascariensis also exhibits, in addition to anatomical adaptations for omnivory and hard-object processing: (1) molars with unusually thick enamel; (2) relatively high encephalization; (3) a protracted period for acquisition of adult foraging skills, with weaning at ~ 2 years; (4) the ability to exploit a wide range of difficult-to-extract food resources; and (5) relatively high activity levels, with long nightly range lengths and large home ranges (Erikson, 1995; Feistner and Ashbourne, 1994; Krakauer and van Schaik, 2005; Sterling, 1993, 1994). Note that we are not suggesting a close relationship of the Archaeolemuridae to the Daubentoniidae, but rather strong anatomical and developmental convergence with ecological underpinnings. We might speculate that Archaeolemur, like Daubentonia and Hapalemur (Mutschler, 2002; Sterling, 1993; Tan, 1999), targeted resources that are available year round (to species able to extract and process them), and therefore exhibited little or no reproductive synchrony. Archaeolemur may have done in the daytime what Daubentonia does at night.

Most of the subfossil lemurs were decidedly unlike Archaeolemur, however. The koala lemurs (three species, family Megaladapidae) were large-bodied, slow-climbing, small-brained folivores with rapidly developing dentitions, and, most probably, early weaning. The sloth lemurs (family Palaeopropithecidae) were very slow-moving climbers and hangers with extreme dental developmental precocity; they were also likely folivore/frugivores with adaptations to exploit seeds and other tough, fibrous foods. Among subfossil lemurs, only Pachylemur (a lemurid) appears to have been committed to frugivory (perhaps like Varecia, its close relative), but it too was a small-brained, slow climber (Jungers et al., 2002; Shapiro et al., 2005). In effect, most of the giant lemurs appear to have been energy conservers, quite like most extant lemurs.

It is important not to exaggerate the terrestrial monkey-likenesses of Archaeolemur. Although Archaeolemur was certainly more like large, semiterres-trial cercopithecoids than other lemurs, many features distinguish these groups. For example, there is no evidence that Archaeolemur, with its broad pelvis, short and wide scapula, short, robust limbs, and exceptionally short digital rays, was cursorial. Its microwear is far closer to that of C. apella and other hard-object processors than to that of terrestrial cercopithecoids. While its brain was large in comparison to those of other lemurs, it was much smaller than those of like-sized baboons. And while dental development was certainly slow in Archaeolemur in comparison to other lemurs, it was not nearly as slow as that of baboons. Unlike the latter, also, Archaeolemur was apparently monomorphic, with only moderately tall canines.

In conclusion, we maintain that the ecological profiles of primate communities in Madagascar were different in the past than in the present, mainly in the prevalence of large-bodied, diurnal forms, but also in the relatively higher representation of omnivorous, hard-object processors. Nevertheless, Wright's (1999) energy frugality hypothesis appears to account for features exhibited by most extinct as well as extant lemurs in Madagascar far better than does the evolutionary disequilibrium hypothesis. We draw this inference largely on the basis of what we believe is increasingly strong evidence (especially postcranial but also dietary and developmental) of energy-conserving lifestyles. Extinct lemurs resembled extant lemurs in displaying relatively low encephalization, little (or no) sexual dimorphism, high folivory, accelerated dental development (with early initiation of molar crown formation, early age at crown completion, and early weaning), and low visual acuity (even if none were nocturnal or cathemeral). Early weaning and rapid dental development probably signals relatively low postnatal maternal investment and social dynamics very unlike those of like-sized anthropoids. It is tempting also to infer that most lived in small groups with limited home ranges, and that female dominance was prevalent among them. One might imagine, for example, that the combination of long canines and little or no sexual dimorphism in Megaladapis signalled small groups occupying small territories defended by both sexes. Perhaps the strongest argument in favor of small groups, limited ranges, and widespread female dominance among extinct lemurs is that they, like many of their extant counterparts, were not merely small-brained and sexually monomorphic, but also probably hypometabolic. We caution that skeletal correlates of group size, range size, and female dominance are tenuous, and such inferences must be regarded as speculative. We can assert with confidence, however, on the basis of our reconstructions of the locomotor, trophic, and, especially, developmental characteristics of these remarkable species, that the giant lemurs had lifestyles very different from those of like-sized, diurnal anthropoids. Lemurs—both extant and extinct—are indeed unique among members of the order Primates.

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