ABSTRACT
The classical theory that teeth evolved from dermal denticles linked with the origin of jaws no longer accounts for the diversity of new data emerging from agnathan and early gnathostome fossils. Tenets on which this is based and the concept of cooption of dermal denticles into the mouth are critically discussed. It is proposed that dermal and oral denticles exhibit patterning differences that imply divergence at loci deep within vertebrate phylogeny. Some whorl-like sets of oropharyngeal denticles, found in both fossil agnathans and gnathostomes, are proposed as a significant feature of morphological pattern. It is suggested that the developmental controls to produce these specialised arrangements in the oropharynx were co-opted in primitive gnathostomes for the dentition on the mandibular arch. These joined denticle sets could presage the tooth whorl sets spaced around the jaw margin, or files of separate teeth, each with replacement teeth aligned in a pattern of ordered size, shape and timing, as observed in primitive fossil and extant gnathostomes.
