Evo-devo models of tooth development and the origin of hominoid molar diversity

The detailed anatomical features that characterize fossil hominin molars figure prominently in the reconstruction of

their taxonomy, phylogeny, and paleobiology. Despite the prominence of molar form in human origins research, the

underlying developmental mechanisms generating the diversity of tooth crown features remain poorly understood.

A model of tooth morphogenesis—the patterning cascade model (PCM)—provides a developmental framework to

explore how and why the varying molar morphologies arose throughout human evolution. We generated virtual

maps of the inner enamel epithelium—an indelibly preserved record of enamel knot arrangement—in 17 living and

fossil hominoid species to investigate whether the PCM explains the expression of all major accessory cusps. We

found that most of the variation and evolutionary changes in hominoid molar morphology followed the general

developmental rule shared by all mammals, outlined by the PCM. Our results have implications for the accurate

interpretation of molar crown configuration in hominoid systematics.