An evolutionary perspective on differential craniodental and postcranial growth and development in primates

This comparative study of growth and development in 16 diverse primate species includes intra- and interspecific comparisons of the sequence and timing of (1) eruption of the deciduous and permanent teeth, (2) fusion of craniofacial sutures, and (3) closure of postcranial epiphyses. Although the primary focus of this research is the relative timing of dental, craniofacial, and postcranial development, metric data were also collected to assess the growth in size accompanying different patterns of maturation. The underlying premise is that evolutionary change is associated with changes in the developmental programs of descendants relative to those of their ancestors. For the purposes of this study, the degree to which the ontogenies of two groups are similar is judged by how closely the relative timing of development of same traits conforms in the groups. Novel treatments of the data include constructing “relative maturation” scales and introducing discriminant function analysis to analyze developmental timing data. ^ I assess both the phylogenetic and adaptive significance of similarities and differences in maturational timing. The developmental data assembled here can be used to assign individuals of all ages to their correct taxon, indicating that temporal patterns of maturation contain a wealth of phylogenetic information. Furthermore, like phylogenies, the taxonomic signals in developmental data are hierarchically nested: haplorhines are developmentally distinct from strepsirrhines, monkeys from apes, African apes from Asian apes, and gorillas from chimpanzees. ^ Conspecific males and females are found to differ in their temporal patterns of maturation regardless of how sexually dimorphic they become. Striking developmental dimorphism exists even in species exhibiting only minimal adult body size and canine dimorphism, such as Hylobates lar. Possible functional explanations for differences in the relative timing of development of postcranial traits are also explored. Cross-group differences occur less frequently among postcranial features intimately involved in joint function than in those that are not. No strong correlation was found between the relative timing of postcranial development and postcranial growth. In discussing the life-history implications of developmental timing parameters, I conclude that the relative timing of dental, craniofacial, and postcranial development, and of growth in size differs in species with “fast” life histories versus those with “slow” life histories. ^ I highlight instances where these results differ from those previously reported and suggest directions in which further elucidation of primate ontogenies might profitably be pursued. Finally, I illustrate how the methods and data presented in this dissertation can be applied to the interpretation of extinct primates, such as Archaeolemur.