Developmental aspects of sexual dimorphism in hominoid canines

We examined the histology of canine teeth in extant hominoids and provided a comparative database on several aspects of canine development. The result ant data augment the known pattern of differences in aspects of tooth crown formation among great apes and more irnportantly, enable us to determine t he underlying developmental mechanisms responsible for canine dimorphism in them. We sectioned and analyzed large sample (n = 108) of reliably-sexed g reat ape mandibular canines according to standard histological techniques. Using information from long- and short-period incremental markings in teeth , we recorded measurements of daily secretion rates, periodicity and linear enamel thickness for specimens of Pan troglodytes, Gorilla gorilla, Pongo pygmaeus and Homo sapiens. Modal values of periodicities in males and femal es, respectively, are: Pan 7/7; Gorilla 9/10; Pongo 10/10; and Homo 8/8. Se cretion 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 cro wn in all great ape species. Female hominoids tend to possess significantly thicker enamel than their male counterparts, which is almost certainly rel ated to the presence of faster daily secretion rates near the enamel-dentin e junction, especially in Gorilla and Pongo. Taken together, these results indicate that sexual differences in canine development are most apparent in the earlier stages of canine crown formation, while interspecific differen ces are most apparent in the outer crown region. When combined with results on the rate and duration of canine crown formation, the results provide es sential background work for larger projects aimed at understanding the deve lopmental basis of canine dimorphism in extant and extinct large-bodied hom inoids and eventually in early hominins.