Fig. 4. Histograms showing the distribution of m1 (A) and m3 (B) size in Gandheralophus gen. nov. specimens of the two Pakistan species described here: G. minor and G. robustus (solid bars). The holotype of each species falls in the modal class. Comparison to a mixed male and female sample of the North American reference species, Hyracotherium tapirinum (Cope, 1875) (open bars; after Gingerich 1981) shows that the variability of Gandheralophus specimens is too great to represent a single species. Empirically, mammalian species have natural−log (length X width) ranges of 0.4 units (mean ± 2 standard deviations; Gingerich 1981). Each species shown here fits within a 0.4−unit range. Distributions of size of G. minor and G. robustus are strongly bimodal. Taken together they would have a range of 0.55 units (2.90 to 3.45) for m1 and of 0.80 units (3.45 to 4.25) for m3. Thus G. minor and G. robustus represent separate species.