Evolution of patterns and processes in teeth and tooth‐related tissues in non‐mammalian vertebrates

Abstract

The evolutionary links that exist between odontodes and organs that are phylogenetically related to them (teeth and scales) suggest the use of comparative approaches to study these structures. Part one of this review briefly introduces current ideas on how the pattern of odontodes and odontode‐derived tissues has been established during evolution to yield the diversity of odontode‐related organs currently observed in nature in the cranial and postcranial skeleton. This introductory survey is used to highlight aspects of the developmental processes underlying the formation of some of these organs and the resemblance their development bears to odontogenesis. Part two provides a concise survey of the diversity of tooth structure in the different classes of extant vertebrates, in particular with reference to enamel/enameloid and dentine structure, and tooth attachment. Against this background, the current state of knowledge is reviewed with regard to developmental mechanisms involved in non‐mammalian odontogenesis. Common structure and similarities in development demonstrate that teeth and odontode derivatives should not be considered subjects of separate lines of research. On the contrary, results acquired in one of these fields are relevant to the other and may disclose model species that are relevant to studies on mammalian odontogenesis.

Conservation of early odontogenic signaling pathways in Aves

“…In addition to the phylogenetic absence of dentition in certain groups such as Aves and Testudines (turtles), developmental regressions of tooth primordia occur in certain species that also could be potentially explained by an evolutionarily acquired inactivation of the genetic pathways controlling tooth formation (20). For example, the diastema region of the mouse oral cavity exhibits transient epithelial thickenings that resemble dental laminae but subsequently undergo apoptosis (36,37).…”

“…Interestingly, the epithelial thickenings observed in Msx1-Msx2 double mutants morphologically resemble transient epithelial thickenings, which have been classically described in the chick oral cavity at day 5 in ovo and in the oral cavity of birds (17)(18)(19). Although modern birds and certain other lineages (e.g., turtles) lack dentition, all toothless vertebrates derived from ancestors that were once toothed (20). Ancient birds, such as the Jurassic bird Archaeopteryx and the late Cretaceous bird Hesperoronis, possessed teeth, and hence the phylogenetic derivation of modern birds indicates that the absence of dentition was a secondary event, occurring approximately 60 million or more years ago (20).…”

“…Although modern birds and certain other lineages (e.g., turtles) lack dentition, all toothless vertebrates derived from ancestors that were once toothed (20). Ancient birds, such as the Jurassic bird Archaeopteryx and the late Cretaceous bird Hesperoronis, possessed teeth, and hence the phylogenetic derivation of modern birds indicates that the absence of dentition was a secondary event, occurring approximately 60 million or more years ago (20). Previous studies in which chick oral epithelium and mouse dental mesenchyme were recombined ostensibly resulted in enamelized teeth, suggesting that in chickens, some of the genes required for odontogenesis may have remained intact (21).…”

Expression of the dlx gene family during formation of the cranial bones in the zebrafish (Danio rerio): Differential involvement in the visceral skeleton and braincase

“…This regression is compensated for by an expansion of the dermal bones of the cranial vault, which become the essential constituents of the braincase in mammals (Beaumont and Cassier, 1994). A dermal covering consisting of scales or other dermal components has been lost in most tetrapods (De Beer, 1937;Hanken and Hall, 1993), but elements of a postcranial dermal skeleton are still present in some amphibians, reptiles, and even mammals (Huysseune and Sire, 1998).…”

Soft Dentin Results in Unique Flexible Teeth in Scraping Catfishes

“…As opposed to tooth flexibility, movable (vs. rigid) tooth-to-jaw attachment is known from other fish taxa as well (Fink 1981;Motta 1984;Huysseune and Sire 1998). Both tooth and tooth attachment flexibility actually serve the same purpose: providing some degree of tooth fracture resistance by decreasing the rigidity of the jaw-teeth apparatus.…”