International Journal of Primatology, Vol. 22, No. 5, 2001 Developmental Aspects of Sexual Dimorphism in Hominoid Canines Gary T. Schwartz, 1,2, ∗ Don J. Reid, 3 and Christopher Dean 4 Received March 15, 2000; revision August 21, 2000; accepted October 4, 2000 We examined the histology of canine teeth in extant hominoids and provided a comparative database on several aspects of canine development. The re- sultant data augment the known pattern of differences in aspects of tooth crown formation among great apes and more importantly, enable us to de- termine the underlying developmental mechanisms responsible for canine di- morphism in them. We sectioned and analyzed a large sample (n = 108) of reliably-sexed great ape mandibular canines according to standard histolog- ical techniques. Using information from long- and short-period incremental markings in teeth, we recorded measurements of daily secretion rates, period- icity and linear enamel thickness for specimens of Pan troglodytes, Gorilla gorilla, Pongo pygmaeus and Homo sapiens. Modal values of periodicities in males and females, respectively, are: Pan 7/7; Gorilla 9/ 10; Pongo 10/ 10; and Homo 8/8. Secretion rates increase from the inner to the outer region of the enamel cap and decrease from the cuspal towards the cervical margin of the canine crown in all great ape species. Female hominoids tend to pos- sess significantly thicker enamel than their male counterparts, which is almost certainly related to the presence of faster daily secretion rates near the enamel- dentine junction, especially in Gorilla and Pongo. Taken together, these results 1 Department of Anthropology, The George Washington University, 2110 G Street, NW, Washington, D.C. 20052. 2 Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560. 3 Department of Oral Biology, The Dental School, Framlington Place, Newcastle Upon Tyne NE2 4BW UK. 4 Evolutionary Anatomy Unit, Department of Anatomy & Developmental Biology, University College London, Rockefeller Building, 21 University Street, London WC1E 6JJ UK. ∗ All correspondences should be addressed to Gary T. Schwartz, Department of Anthropology, The George Washington University, 2110 G Street NW, Washington, DC 20052. Tel: (202)994- 4170; Fax: (202)994-6097, e-mail: garys@gwu.edu. 837 0164-0291/01/1000-0837$19.50/0 C  2001 Plenum Publishing Corporation