Sexual dimorphism in large‐bodied primates: The case of the subfossil lemurs

Abstract

Large body size has evolved repeatedly in the order Primates, not merely among anthropoids but also among prosimians. Whereas high degrees of sexual size dimorphism characterize many of the large-bodied anthropoids, this is not the case for extinct large-bodied lemurs. This paper uses finite mixture analysis and other techniques to ascertain just how much skull length dimorphism might be embedded in the generally unimodal distributions of skull lengths of giant extinct lemurs from single localities, and then compares these results with known skull length dimorphisms in extant lemurs and large-bodied catarrhines. We show that low levels of skull length sexual dimorphism (or none at all) characterize subfossil lemurs, and we explore several possible explanations for this phenomenon. Traditional explanations of sexual size dimorphism generally focus on body size or mating systems. These are not sufficient to explain the variation in sexual dimorphism that can be observed in the order Primates.

Patterns of size sexual dimorphism in Australopithecus afarensis: Another look

“…These methods have been shown to have various levels of precision and accuracy, with simple methods performing as well as, if not better than, more complex methods (Cope and Lacy, 1995;Godfrey et al, 1993;Plavcan, 1994). However, they still need to solve the problem that conventional measures of sexual dimorphism do not provide, that is confidence intervals that allow comparison of different samples.…”

Sexual dimorphism in primate evolution

“…1 is only characteristic of some callitrichine primates and possibly some strepsirrhines (Kappeler, 1990(Kappeler, , 1991Godfrey et al, 1993;Plavcan and van Schaik, 1997b). In general, body mass dimorphism reaches its extremes in hominoids and papionines.…”

“…Plavcan and Kay (1988) and Plavcan (1990Plavcan ( , 2000b demonstrated that male primates are not relatively more variable than females for dental and cranial traits. Kappeler (1990Kappeler ( , 1991 and Godfrey et al (1993) pointed out that there is no correlation between body size and dimorphism in strepsirrhine primates. Andersson (1994) noted that several studies likewise found little such correlation in other groups of animals, and that the model only works as long as body size continually increases in a lineage over time.…”

“…Unfortunately, allometric regression of dimorphism is too often taken as a given, with little attention given to the underlying assumptions. Recent comparative analyses (Kappeler, 1990(Kappeler, , 1991Godfrey et al, 1993;Mitani et al, 1996;Plavcan and van Schaik, 1997b;Plavcan, 1999) suggest that the adage that correlation does not equal causation needs to be heeded in this case, and allometric adjustment of dimorphism should be avoided without careful justification. Rather, attention should be directed first to testing hypotheses about the causal relationships between dimorphism, size, behavior, and ecology.…”

Morphological Variation in Populations of Eulemur albocollaris and E. fulvus rufus

“…These patterns in sexual dimorphism and levels of sperm competition are mostly consistent in haplorhines (Harcourt, 1994;Harcourt et al, 1981Harcourt et al, , 1995van Schaik, 1992, 1997) but not in strepsirhines (Godfrey et al, 1993;Kappeler, 1996Kappeler, , 1997Feitz, 1999, Wright, 1999. For example, despite their diverse social systems, lemurs are generally monomorphic (Glander et al, 1992;Kappeler, 1990Kappeler, , 1991Kappeler, , 1996Plavcan and van Schaik, 1997;Wright, 2002, 2003;van Schaik and Kappeler, 1996;Wright, 1999).…”