ESTIMATING SEXUAL DIMORPHISM BY METHOD-OF-MOMENTS

Estimating the degree of sexual dimorphism is difficult in fossil spec ies because most specimens lack indicators of sex. We present a proced ure that estimates sexual dimorphism in samples of unknown sex using m ethod-of-moments. We assume that the distribution of a metric trait is composed of two underlying normal distributions, one for males and on e for females. We use three moments around the mean of the combined-se x distribution to estimate the means and the common standard deviation of the two underlying distributions. This procedure has advantages ov er previous methods: it is relatively simple to use, specimens need no t be assigned to sex a priori, no reference to living species analogs is required, and the method provides conservative estimates of dimorph ism under a variety of conditions. The method performs best when the m ale and female distributions overlap minimally but also works well whe n overlap is substantial. Simulations indicate that this relatively si mple method is more accurate and reliable than previous methods for es timating dimorphism. (C) 1996 Wiley-Liss, Inc.