02271nas a2200217   4500008004100000022001400041245007900055210006900134260001700203300001200220490000600232520158500238653001201823653002501835653002001860653000801880653001001888653001601898100002601914856011301940       2003                        eng d  a1520-541X00aVertebrate dentitions at the origin of jaws: when and how pattern evolved.0 aVertebrate dentitions at the origin of jaws when and how pattern  c2003 Jul-Aug  a394-4130 v53 a<p>New evidence shows that teeth evolved with a greater degree of independence from jaws than previously considered. Pharyngeal denticles occur in jawless fish and also in early gnathostomes and precede jaw teeth in phylogeny. Many of these denticles form joined polarized sets on each branchial arch; these resemble whorl-shaped tooth sets on the jaws of stem and crown gnathostomes and are proposed as homologous units. Therefore, the source of patterning of these pharyngeal denticle and tooth sets is conserved from jawless conditions. It is proposed that developmental regulatory systems, responsible for all such tooth patterns on the jaws, are co-opted from the pharyngeal region and not from the skin as classically understood. This strongly implicates embryonic endoderm as opposed to ectoderm in the genetic control of dentition patterning. New interpretations of ontogenetic data on patterning dentitions of extant sharks are proposed, together with those of osteichthyan fish. Two entirely fossil groups, placoderms and acanthodians, at the base of gnathostome phylogeny are reassessed on the basis of a new model. It is concluded that within stem group and crown group gnathostomes several different strategies, unique to each taxon, were adopted to produce different developmental models of dentition patterning from pharyngeal denticles. One shared developmental pattern is that of initiation from primordial tooth sites, independently in each dentate zone of the jaws. The new model is proposed as a framework for data on evolutionary developmental genetics.</p>
10aAnimals10aBiological Evolution10aBody Patterning10aJaw10aTooth10aVertebrates1 aSmith, Moya, Meredith  uhttps://chondrichthyes.myspecies.info/content/vertebrate-dentitions-origin-jaws-when-and-how-pattern-evolved