On Pattern Formation in Reptilian Dentition

Pattern formation of placode initiation in reptilian dental development is modeled with a generalized function, which may represent chemical concentrations, strain energy of mechanically deforming tissues, or other quantities representing a local inhibition of placode formation. The conditions on the generalized model which are necessary to account for all experimental observations are examined in detail. Minimal conditions for the correct sequencing of the tooth primordia are determined, and it is found that all known initial reptilian sequences can be accounted for with the same mechanism, with merely a different choice of parameters. An implication of the modeling results is that the lower jaw of the tuatara (Sphenodon punctatus) has a greater growth rate in its anterior portion than in its posterior portion, whereas the opposite is true of all other reptiles studied. Sequences of tooth initiation are observed robustly in the model which have not hitherto been documentedin vivo, suggesting the as yet undocumented occurrence of such a sequence in a living or extinct reptile.