Developmental Constraints Conserve Evolutionary Pattern in an Osteichthyan Dentition

Abstract

The lungfish dentition is different from other osteichthyan fish because it has a characteristic and unique pattern of teeth arranged as toothplates. Growth, addition of teeth, and retention as part of a statodont dentition are determined by the initiation pattern. In adult lungfish new teeth are only added laterally to each radial row in the dentition. This is in marked contrast to marginal rows of teeth with regular, alternating replacement in most osteichthyans. We analyze development from fossil hatchling forms of the Late Devonian dipnoan Andreyevichthys and compare with those of Neoceratodus, the Australian lungfish. The specific pattern of development, unique within lungfish, is also present in the transitory, marginal, anterior dentition in both, reflecting a strongly conserved developmental pattern. These marginal teeth form but are then lost in both, so that also this program of development is conserved within lungfish for 360 million years, from the earliest known form.

Vertebrate dentitions at the origin of jaws: when and how pattern evolved

“…One particular example of conservation of developmental pattern, unique for one taxon across 360 million years, can be observed in the ontogeny of fossil and recent lungfish dentitions (Reisz and Smith 2001;Smith and Krupina 2001;Smith et al 2002). It is assumed here that part of the module for dentition patterning is conserved within gnathostomes, that is, the morphogenetic unit, or primordium for denticle, or tooth, involving epithelial-mesenchymal interactions between an inductive epithelium (endoderm) and mesenchyme derived from cranial neural crest (ectomesenchyme).…”

“…The point at which new teeth are added is consistently on the lingual side, deep to the oral epithelium, and in line with the functional set in the tooth whorl. This type of information can also be obtained in fossil species with an ontogenetic series and by comparison with extant species (Reisz and Smith 2001;Smith and Krupina 2001;Smith et al 2002). Without this understanding of developmental differences, imprecise terminology for teeth and denticles has frequently been adopted in many descriptions of dental structures, as has been discussed for fossil lungfish dentitions (Smith 1988).…”

“…2d and g). Smith (1985) proposed that one initial tooth primordium at the patterning stage of the dentition set up tooth pattern in lungfish in each dentate region of the larval jaw (Smith 1985;Smith et al 2002). Smith and Krupina (2001) described this lungfish pattern as in marked contrast to the typical linear rows of teeth with lingual replacement for each tooth position, characteristic of most osteichthyan and chondrichthyan dentitions.…”

Developmental plasticity and disparity in early dipnoan (lungfish) dentitions

“…Although all major clades are proposed to share one mode of development by initiation from a single pioneer, or primordial, tooth for each dentate bone, the pattern in which all subsequent primary teeth and replacement teeth are generated is different for each higher‐level clade. This is an important assumption for the current analysis, and one accepted for lungfish (Kemp 1977, 2002; Smith et al 2002). Because the lungfish clade falls within the osteichthyan (bony fish plus tetrapod) clade, we know that the lungfish pattern of tooth generation must be derived from the “normal” osteichthyan pattern, at least in the historical sense of replacing it.…”

Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development

“…2F). This dentition includes the prearticular and pterygoid teeth typical of all lungfish, but also elements of the marginal dentition such as that on the dentary (Kemp, '77, 2002;Reisz and Smith, 2001;Smith et al, 2002). Thus, teeth develop early in ontogeny of living Neoceratodus but are absent even in the largest P. gunni.…”