Our goal in this chapter is to review recent research on the ecology of Madagascar's extinct lemurs, with particular attention to how strongly these species resembled their still-extant relatives. The literature on the ecology of lemurs is replete with proclamations regarding their special adaptations. These include hypometabolism (torpor in some), sperm competition or other forms of male-male competition for mates that involve relatively low agonism, small group size, seasonal breeding, cathemerality, territoriality, female dominance, fibrous diets (high folivory), and low encephalization. Extant lemurs, whether nocturnal, cathemeral, or diurnal, tend to exhibit low visual acuity (relatively high retinal summation). Some have extremely rapid dental development and are dentally precocious at birth and weaning. Lemurs are excellent climbers (although a few spend a fair amount of time on the ground). If these special adaptations are
Laurie R. Godfrey • Department of Anthropology, University of Massachusetts, Amherst, Amherst, MA 01003 William L. Jungers • Department of Anatomical Sciences, School of Medicine, Stony Brook University, Stony Brook, NY 11794 Gary T. Schwartz • Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287
indeed phylogenetically constrained and therefore Malagasy lemur-specific, then one might predict that the giant lemurs were also characterized by many of these strategies and traits. If, on the other hand, body size is more important than phy-logeny in influencing adaptations and lifestyles, then the extinct lemurs, especially the truly "giant" ones, should exhibit only limited similarities to their living relatives and converge instead on larger-bodied anthropoid primates.
There are two prevailing hypotheses that purport to explain the special adaptations of lemurs. The first, Wright's (1999) energy frugality hypothesis, builds on the energy conservation hypothesis of Jolly and others (Jolly, 1984; Richard and Nicoll, 1987; Young et al., 1990). According to this hypothesis, most lemur traits serve either to conserve energy (e.g., hypometabolism, relatively low agonism, seasonal breeding, small group size) or to maximize use of scarce resources (fibrous diets, cathemerality, territoriality, female dominance), thus enabling lemurs to survive in harsh, seasonal habitats with low productivity. Seasonal nutritional stress is prevalent among lemurs; it influences the timing of reproduction and weaning, and may be linked to female dominance and small group size. Early weaning may imply early acquisition of ecological (though not necessarily reproductive) "adulthood," with important implications for reduced maternal investment.
Van Schaik and Kappeler's (1996) evolutionary disequilibrium hypothesis, on the other hand, holds that extant lemurs are in the process of modifying their behavior and other niche characteristics in the wake of the extinction of major potential diurnal predators and possible competitors. Cathemerality, for example, is a step in the shift from nocturnality to diurnality. Small group size and female dominance are primitive retentions from more nocturnal, monogamous ancestors, and these adaptations are in the process of being replaced as the species become more diurnal and more gregarious, and thus more monkey-like.
If Wright's energy frugality hypothesis holds generally for Malagasy primates, then it should predict or explain the characteristics of extinct as well as extant species. If van Schaik and Kappeler's evolutionary disequilibrium hypothesis is correct, then the preextinction biota should differ from modern species in a fundamental manner. The larger-bodied, extinct lemurs should bear little resemblance to modern lemurs in terms of their salient ecological adaptations, but should rather resemble like-sized, diurnal anthropoids. The question is, to what extent can we draw behavioral/ecological inferences for extinct lemurs? What is registered in skeletons? How does what we can infer regarding extinct lemurs affect our perception of the ecospace occupied by the lemurs of Madagascar?
Space limitations prevent us from reviewing the entire literature on subfossil lemur paleoecology. Much research on subfossil lemur paleoecology and life histories has been done in the past two decades (Burney et al., 2004; Godfrey, 1988; Godfrey et al., 1993, 1997a,b, 1999, 2002, 2004a, 2005a,b, in press a,b; Godfrey and Jungers, 2003; Hamrick et al., 2000; Jungers et al., 1991, 1997, 2002, 2005a,b; King et al., 2001; Rafferty et al., 2002; Schwartz et al., 2002, 2005; Shapiro et al., 2005; Simons, 1994; Simons et al., 1992; Wunderlich et al., 1996), supplementing and expanding some excellent early work (see Godfrey and Jungers, 2002, and Tattersall, 1982, for historical reviews).
We focus here on questions of particular relevance to the focus of this book: the uniqueness of lemur behavioral ecology. Specifically, we ask: (1) Were extinct lemurs forest or woodland-limited? (2) Did extinct lemurs exhibit female dominance? (3) Were extinct lemurs energy conservers? (4) Did extinct lemurs exploit fibrous food sources? (5) Did extinct lemurs wean their offspring earlier than like-sized, diurnal anthropoids? (6) Did extinct lemurs exhibit low visual acuity? (7) Finally, if the process of extinction was not random, how can it be characterized? Table 1 provides a brief overview of the extinct lemurs (including the sloth, koala, and monkey lemurs) and their characteristics.
Table 1. Madagascar's extinct lemurs (modified from Burney et al., 2004; Godfrey, 2005)
Family and included genera
Palaeopropithecidae (sloth lemurs) Palaeopropithecus Archaeoindris Mesopropithecus Babakotia
Megaladapidae (koala lemurs) Megaladapis
( Megaladapis) Megaladapis ( Peloriadapis)
Archaeolemuridae (monkey lemurs) Archaeolemur Hadropithecus
Lemuridae (ruffed lemurs, etc.) Pachylemur
This diverse family is entirely extinct. Called sloth lemurs because of similarities to arboreal sloths, these lemurs are most closely related to living indriids. The largest of all lemurs, Archaeoindris, belongs to this family. Sloth lemurs had long, curved digits, and most were specialized hangers. They fed on a combination of leaves, fruit, and seeds. Sloth lemurs survived the advent of humans to Madagascar by at least 1500 years. There is evidence of human butchery of sloth lemurs in southwest Madagascar more than 2000 years ago, shortly after humans first colonized the island.
The koala lemurs are much larger than the sportive lemurs
(Lepilemuridae) and the Lemuridae, both of which have been considered their sister clades. Koala lemurs resembled sportive lemurs in their dental morphology and diet of leaves. Slow climbers with huge, pincerlike feet, they were committed to life in the trees despite their large body size. The largest Megaladapis species was the size of a large male orangutan or female gorilla. Megaladapis was still alive when humans arrived on Madagascar, and well into the last millennium.
These robust, baboon-sized lemurs may have been among the last giant lemurs to become extinct. Called monkey lemurs because of convergences to baboons and macaques, these were likely the most terrestrial of the giant lemurs. Archaeolemurids were able to break open hard objects (such as nuts) with their teeth; there is also direct evidence for omnivory in Archaeolemur.
This family includes the living aye-aye and its giant extinct relative,
Daubentonia robusta. The latter was still extant when humans arrived on Madagascar; its incisors were collected, drilled, and probably strung on necklaces. Aye-ayes are the largest nocturnal lemurs of Madagascar.
This family of quadrupedal lemurs has one extinct member, the giant ruffed lemur, Pachylemur (three times the mass of the largest living member of this group, Varecia). Like Varecia, Pachylemur consumed fruit.
Were extinct lemurs forest or woodland-limited, as are extant lemurs?
The evidence strongly favors wooded-habitat preference for most, if not all, extinct lemurs. Both the postcranial anatomy (Jungers et al., 2002) and stable isotopes (Burney et al., 2004) bear testimony to such a habitat preference. Highly derived postcranial specializations suggest that leaping was rare (if ever practiced) by extinct lemurs, but that slow climbing and suspension were common (Jungers et al., 2002; Shapiro et al., 2005). Of course, due merely to their body size, the giant extinct lemurs would have had to spend a fair amount of time on the ground (if merely to cross from tree to tree), but ground locomotion would have been awkward, indeed ungainly, for some. Even the largest-bodied lemurs (i.e., the male-gorilla-sized Archaeoindris) have adaptations that suggest scansoriality (e.g., a femur with an extremely high collodiaphyseal angle and reduced greater trochanter). Terrestrial quadrupedalism may have been common in the archaeolemurids, but there is no evidence of cursoriality in either Archaeolemur or Hadropithecus. New discoveries of postcranial bones of Hadropithecus (Godfrey et al., 2005b, in press a) have confirmed the prior inferences of Godfrey et al. (1997a) that some of the earlier postcranial attributions for Hadropithecus (and conclusions based on them) were incorrect. The femora of Hadropithecus are robust, anteroposteriorly compressed, and far more like those of gorillas than baboons.
Stable carbon isotopes are now available for many extinct lemur taxa (Burney et al., 2004; Table 2). They corroborate consumption of C3 (generally closed forest) plants in all species except Hadropithecus, which had a mixed diet of C3 and C4 or CAM plants (or some combination of plants and animals, such as snails, consuming C4 plants). Hadropithecus is best represented in the arid south, including some more open habitats (e.g., Ambovombe) lacking other primates.
Did extinct lemurs exhibit female dominance?
For many species of living lemurs, females win the great majority of agonistic encounters with males—a phenomenon called "female dominance" (Digby and Kahlenberg, 2002; Genin, 2003; Jolly, 1984, 1998; Kubzdela et al., 1992; Overdorff et al., 2005; Pochron et al., 2003; Pollock, 1979; Radespiel and Zimmermann, 2001; Richard, 1987; Richard and Dewar, 1991; Richard et al., 2000; Sauther et al., 1999; Waeber and Hemelrijk, 2003). There is no simple way to determine whether extinct lemurs showed the same pattern of behavior. This is because female dominance in lemurs is not based on the physical superiority of females; therefore, variation in the degree and expression of female dominance is uncorrelated with variation in skeletal characteristics. It is possible that female dominance in lemurs depends on an absence of physical superiority of males; extant lemurs are notorious for their sexual monomorphism or low levels of sexual dimor-
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