Samples of the new middle Eocene tapiroid Hesperaletes are analyzed to determine the merits of their referral to particular species. Criteria for recognizing species not only include documenting apomorphic morphologies, but also statistically estimating similarity and variability between and within samples. These criteria are consistent with the general lineage species concept that considers species to be segments of population lineages. Statistical comparisons use Student t tests and an analysis of the coefficient of variation in different samples and combinations of pooled samples. Application of these criteria to samples of Hesperaletes leads to confident referral of late Uintan material to a single species, Hesperaletes borineyi, but indicate that early Uintan samples cannot confidently be referred to a single species. Accordingly, most of the early Uintan samples are referred to a second species, Hesperaletes walshi, with the exception of one sample of uncertain taxonomic status. Although several evolutionary scenarios are consistent with these patterns of variability, they are interpreted to be the result of a cladogenetic speciation event.
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