Cranial ontogeny and heterochronies in Gorilla gorilla and Pan troglodytes.

The dynamics and chronology of the development of Gorilla gorilla and Pan troglodytes are clarified by comparing their cranial ontogenesis using Procrustes methods. Phenetic trees confirm a morphological gradient from neonate to adult, with more obvious sexual dimorphism in gorillas. By quantifying morphological change through vector field, the spatial arrangement of cranio-facial growth in the two species can be represented and compared. We conclude that differences in the timing of development (acceleration, pie-displacement, rate hypermorphosis by acceleration and time hypermorphosis by post-displacement) give rise to the intra- and interspecific variation observed in the "great apes" ontogenetic plan. (C) 2001 Editions scientifiques et medicales Elsevier SAS.