Evolutionary Origin of Teeth

Rücklin, Martin; Donoghue, Philip C. J.

doi:10.1002/9780470015902.a0026408

Cited by 2 publications

(2 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The origin of oral dentition has been an intriguing debate (e.g., Debiais‐Thibaud et al, 2011; Donoghue & Rücklin, 2016; Fraser et al, 2010; Fraser & Smith, 2011; Huysseune et al, 2022; Rücklin & Donoghue, 2019; Witten et al, 2014). The ‘outside‐in’ hypothesis claims teeth evolved from dermal denticles that expanded into the oropharynx and became specialized in feeding (Blais et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Complex enameloid microstructure of †Ischyrhiza mira rostral denticles

et al. 2022

View full text Add to dashboard Cite

Serving in a foraging or self-defense capacity, pristiophorids, pristids, and the extinct sclerorhynchoids independently evolved an elongated rostrum lined with modified dermal denticles called rostral denticles. Isolated rostral denticles of the sclerorhynchoid Ischyrhiza mira are commonly recovered from Late Cretaceous North American marine deposits. Although the external morphology has been thoroughly presented in the literature, very little is known about the histological composition and organization of these curious structures. Using acid-etching techniques and scanning electron microscopy, we show that the microstructure of I. mira rostral denticles are considerably more complex than that of previously described dermal denticles situated elsewhere on the body. The apical cap consists of outer single crystallite enameloid (SCE) and inner bundled crystallite enameloid (BCE) overlying a region of orthodentine. The BCE has distinct parallel bundled enameloid (PBE), tangled bundled enameloid (TBE), and radial bundled enameloid (RBE) components. Additionally, the cutting edge of the rostral denticle is produced by a superficial layer of SCE and a deeper ridges/cutting edge layer (RCEL) of the BCE. The highly organized enameloid observed in the rostral denticles of this batomorph resembles that of the multifaceted tissue architecture observed in the oral teeth of selachimorphs and demonstrates that dermal scales have the capacity to evolve histologically similar complex tooth-like structures both inside and outside the oropharyngeal cavity.

show abstract

Section: Discussionmentioning

confidence: 99%

Complex enameloid microstructure of †Ischyrhiza mira rostral denticles

et al. 2022

View full text Add to dashboard Cite

show abstract

“…Because of their poor mineralisation and deep location, data on gill skeletons in fossil early gnathostomes are rare (Pradel et al ., 2014 ; Brazeau et al ., 2017 ), and this is even more so for pharyngeal denticles, although advanced imaging techniques may expand our knowledge in the years to come. Within the crown gnathostomes, pharyngeal teeth or denticles are limited to chondrichthyans and osteichthyans (Rücklin & Donoghue, 2019 ). The basal condition in recent sharks is argued to be denticles covering much or all of the buccopharyngeal surface (Nelson, 1970 ).…”

Section: Germ Layers and The Distribution Of Post‐mandibular Teethmentioning

confidence: 99%

The conundrum of pharyngeal teeth origin: the role of germ layers, pouches, and gill slits

2021

View full text Add to dashboard Cite

There are several competing hypotheses on tooth origins, with discussions eventually settling in favour of an ‘outside‐in’ scenario, in which internal odontodes (teeth) derived from external odontodes (skin denticles) in jawless vertebrates. The evolution of oral teeth from skin denticles can be intuitively understood from their location at the mouth entrance. However, the basal condition for jawed vertebrates is arguably to possess teeth distributed throughout the oropharynx (i.e. oral and pharyngeal teeth). As skin denticle development requires the presence of ectoderm‐derived epithelium and of mesenchyme, it remains to be answered how odontode‐forming skin epithelium, or its competence, were ‘transferred' deep into the endoderm‐covered oropharynx. The ‘modified outside‐in’ hypothesis for tooth origins proposed that this transfer was accomplished through displacement of odontogenic epithelium, that is ectoderm, not only through the mouth, but also via any opening (e.g. gill slits) that connects the ectoderm to the epithelial lining of the pharynx (endoderm). This review explores from an evolutionary and from a developmental perspective whether ectoderm plays a role in (pharyngeal) tooth and denticle formation. Historic and recent studies on tooth development show that the odontogenic epithelium (enamel organ) of oral or pharyngeal teeth can be of ectodermal, endodermal, or of mixed ecto–endodermal origin. Comprehensive data are, however, only available for a few taxa. Interestingly, in these taxa, the enamel organ always develops from the basal layer of a stratified epithelium that is at least bilayered. In zebrafish, a miniaturised teleost that only retains pharyngeal teeth, an epithelial surface layer with ectoderm‐like characters is required to initiate the formation of an enamel organ from the basal, endodermal epithelium. In urodele amphibians, the bilayered epithelium is endodermal, but the surface layer acquires ectodermal characters, here termed ‘epidermalised endoderm’. Furthermore, ectoderm–endoderm contacts at pouch–cleft boundaries (i.e. the prospective gill slits) are important for pharyngeal tooth initiation, even if the influx of ectoderm via these routes is limited. A balance between sonic hedgehog and retinoic acid signalling could operate to assign tooth‐initiating competence to the endoderm at the level of any particular pouch. In summary, three characters are identified as being required for pharyngeal tooth formation: (i) pouch–cleft contact, (ii) a stratified epithelium, of which (iii) the apical layer adopts ectodermal features. These characters delimit the area in which teeth can form, yet cannot alone explain the distribution of teeth over the different pharyngeal arches. The review concludes with a hypothetical evolutionary scenario regarding the persisting influence of ectoderm on pharyngeal tooth formation. Studies on basal osteichthyans with less‐specialised types of early embryonic development will provide a crucial test for the potential role of ectoderm in pharyngeal too...

show abstract

Evolutionary Origin of Teeth

Cited by 2 publications

References 38 publications

Complex enameloid microstructure of †Ischyrhiza mira rostral denticles

Complex enameloid microstructure of †Ischyrhiza mira rostral denticles

The conundrum of pharyngeal teeth origin: the role of germ layers, pouches, and gill slits

Contact Info

Product

Resources

About