Heterochronies and procrustes superimposition: application to the skulls of primates Hominoidea.

The procrustes superimposition method is well adapted to heterochronic stud ies in the field of evolutionary biology. 1) The procrustes method gives a precise and mathematical definition of two of the three heterochronic varia bles: size and shape. 2) It allows us to describe complex anatomical struct ures and thus to analyse the whole structure and not just to proceed trait by trait. 3) The approach is statistical and the different hypotheses and r esults may be statistically tested. 4) When applied to heterochronies the m ethod allows us to test if there is a common shape change related to allome try. In the present study of three species of Hominoid primates, the procru stes superimposition reveals that various heterochronic processes are simul taneously present. Size-age-shape dissociations between species, already pr esent in the first ontogenetic stage, are amplified with growth until adult stage. As compared with that of the chimpanzee, the growth of the gorilla skull is accelerated in terms of size-shape covariation and size alone. The growth of the human skull is neotenic as compared with that of the apes. ( C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.