Patterns of sexual dimorphism and of variability in the dentition ofOtolemur crassicaudatus

Analysis of dentition of a living wild population of ring-tailed lemurs (Lemur catta) from Beza Mahafaly, Madagascar

Detailed descriptions of the dentition of many strepsirhine primate taxa are rare, despite their importance in understanding primate evolutionary biology. While several researchers have provided detailed morphological descriptions of ring-tailed lemur dentition (e.g., Schwartz and Tattersall [1985] Am. Mus. Nat. Hist. Anthropol. Pap. 60:1-100; Tattersall and Schwartz [1991] Am. Mus. Nat. Hist. Anthropol. Pap. 69:2-18), there are few studies (e.g., Eaglen [1986] Am. J. Phys. Anthropol. 71:185-201) that present quantitative data on the dentition of this species. Furthermore, prior analyses were based on museum specimens from various populations and locations. We present here quantitative and morphological data on the dentition of a population of wild Lemur catta from Beza Mahafaly Special Reserve, Madagascar. Measurements were made on dental casts (n = 39) taken from living members of this L. catta population. Our analysis indicates that no significant (P > 0.05) sexual dimorphism exists for the 30 dental measurements collected. These data support the generalizations (e.g., Plavcan and van Schaik [1994] Evol. Anthropol. 2:208-214; Kappeler [1996] J. Evol. Biol. 9:43-65) that little sexual dimorphism in dentition exists among Malagasy strepsirhines. In addition, the overall patterns of metric variation in this sample compare favorably with patterns seen among other primates, e.g., premolar measurements varying more than molars (e.g., Gingerich [1974] J. Paleontol. 48:895-903). However, there is a degree of intraspecific morphological variation indicated, with one of the morphological traits discussed in other studies as being species-specific for L. catta (absence of P(4) metaconids) observed to vary between specimens. Because the patterns of variation seen in this sample are from a known breeding population, the data presented here provide an important reference for interpreting and understanding the fossil record.

Sexual dimorphism and sex ratios in Madagascan prosimians

Skull length was used to evaluate the extent of sexual dimorphism in size among 21 taxa of extant Madagascan prosimians. Extraneous sources of variation were controlled by limiting male-female comparisons to museum samples comprised of ten or more wild-caught, adult individuals collected at the same locality (24 samples total). Sexual dimorphism in skull length averaged only 1.31%, with equal probability of males or females being larger. The only statistically significant sexual differences were Lepilemur edwardsi from St. Marie de Marovoay in western Madagascar (P < 0.05; males 4% larger then females = 2.2 mm) and Microcebus murinus from Amboasary-Sud in southern Madagascar (P < 0.001; females 2% larger than males = 0.6 mm). A recent study of body weights of captive animals at Duke University Primate Center also showed that M. murinus displays highly significant sexual dimorphism. These results were examined in the context of factors believed to affect sexual dimorphism in anthropoid primates. The same 24 samples were used to demonstrate that the sex ratio is approximately 1:1 among Madagascan prosimians, and this information was correlated with data from field studies. The correlations between sexual dimorphism, sex ratio, and size are low, indicating that these are independent traits in Madagascan prosimians.