ON PATTERN-FORMATION IN REPTILIAN DENTITION

Pattern formation of placode initiation in reptilian dental developmen t is modeled with a generalized function, which may represent chemical concentrations, strain energy of mechanically deforming tissues, or o ther 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 con ditions for the correct sequencing of the tooth primordia are determin ed, 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 lowe r jaw of the tuatara (Sphenodon punctatus) has a greater growth rate i n its anterior portion than in its posterior portion, whereas the oppo site is true of all other reptiles studied. Sequences of tooth initiat ion are observed robustly in the model which have not hitherto been do cumented in vivo, suggesting the as yet undocumented occurrence of suc h a sequence in a living or extinct reptile. (C) 1997 Academic Press L imited.