AbstractThe three living species ofTrichechusare clearly defined and well exemplify the degree of variability and taxonomic value of morphological characters in a well‐understood mammalian genus. Statistical analysis of the largest sample of manatee skulls yet studied has allowed us to identify small suites of characters that effectively distinguish these species. The two subspecies ofT. manatusproposed by Hatt (1934) can likewise be distinguished, and their use as taxonomic categories seems justified. This suggests that the cool winters of the northern Gulf Coast, on the one hand, and the deep water and strong currents of the Straits of Florida, on the other, are effective barriers to gene flow between Florida and Antillean manatees. Alleged taxonomic distinctions withinT. senegalensis, however, have no demonstrated basis. No significant sexual dimorphism was detected in skulls of any of the species. Many interspecific differences can be correlated with feeding ecology, but others remain unexplained. Features of tooth crown morphology are among the most constant characters examined, but some osteological characters are equally good.T. manatasandT. senegalensis(which are phenetically the most similar) also seem to share a more recent common ancestor than either does withT. inunguis.However, the three species probably separated from each other at nearly the same time.T. inunguishas since become the most derived species, whileT. senegalensishas changed the leas
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