The protoconid: a key cusp in lower molars. Evidence from a recent modern human population.

The results can be explained in the framework of the patterning cascade model. As the first cusp to appear developmentally, the Prd forms in response to signals from the primary enamel knot, likely contributing to its stability. Inhibitory signals emitted during the Prd formation may lead to the reduction or disappearance of the talonid cusps, if these do not have enough time to form before the end of the M morphogenetic process.