Moya Meredith Smith

King's College London | KCL · Centre for Craniofacial and Regenerative Biology CCRB

The Notch pathway is an ancient, evolutionary conserved intercellular signaling mechanism that is involved in cell fate specification and proper embryonic development. The Jagged2 gene, which encodes a ligand for the Notch family of receptors, is expressed from the earliest stages of odontogenesis in epithelial cells that will later generate the en...

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian of the Tver Region, Russia. CT scanning of the holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by the presence of at least two cl...

Restudy of Campyloprion annectans Eastman, 1902 from North America demonstrated that neither specimen included is diagnostic at the species level; thus, the species name is a nomen dubium. Since this species was designated as the type species of the genus, this requires suppression of the generic name also. Another species earlier assigned to Campy...

Crushing and eating hard prey (durophagy) is mechanically demanding. The cartilage jaws of durophagous stingrays are known to be reinforced relative to non-durophagous relatives, with a thickened external cortex of mineralized blocks (tesserae), reinforcing struts inside the jaw (trabeculae), and pavement-like dentition. These strategies for skelet...

Two sets of teeth (diphyodonty) characterise extant mammals but not reptiles, as they generate many replacement sets (polyphyodonty). The transition in long‐extinct species from many sets to only two has to date only been reported in Jurassic eucynodonts. Specimens of the Late Triassic brasilodontid eucynodont Brasilodon have provided anatomical an...

Leedsichthys problematicus is a suspension‐feeding member of the Mesozoic clade Pachycormiformes (stem‐group Teleostei), and the largest known ray‐finned fish (Actinopterygii). As in some larger fish, the skeleton is poorly ossified, but the caudal fin (tail) is well‐preserved. Bony calluses have been found here, on the dermal fin rays, and when se...

Among the cartilaginous fishes (Chondrichthyes), the Holocephali are unique in that teeth are absent both in ontogeny and adult regenerative growth. Instead, the holocephalan dentition of ever‐growing nonshedding dental plates is composed of dentine, trabecular in arrangement, forming spaces into which a novel hypermineralized dentine (whitlockin)...

The Holocephali is a major group of chondrichthyan fishes, the sister taxon to the sharks and rays (Elasmobranchii). However, the dentition of extant holocephalans is very different from that of the elasmobranchs, lacking individual tooth renewal, but comprising dental plates made entirely of self-renewing dentine. This renewal of all tissues occur...

All extant holocephalans (Chimaeroidei) have lost the ability to make individual teeth, as tooth germs are neither part of the embryonic development of the dental plates, nor of their continuous growth. Instead, a hypermineralized dentine with a unique mineral, whitlockin, is specifically distributed within a dentine framework into structures that...

The Sinacanthida ordo nov. and Mongolepidida are spine- and scale-based taxa whose remains encompass some of the earliest reported fossils of chondrichthyan fish. Investigation of fragmentary material from the Early Silurian Tataertag and Ymogantau Formations of the Tarim Basin (Xinjiang Uygur Autonomous Region, China) has revealed a diverse mongol...

The dentition in extant holocephalans (Chondrichthyes) comprises three pairs of continuously growing dental plates, rather than the separate teeth characterizing elasmobranchs. We investigated how different types of dentine in these plates, including hypermineralized dentine, are arranged, and how this is renewed aborally, in adult and juvenile den...

The life of a tooth is dynamic, with several phases: Firstly, during embryogenesis the main components of the tooth are formed (i.e. enamel, cementum, pulp, and dentine). Eruption of the tooth leads to the development of root(s) and root canal systems (i.e. main root canal(s), lateral root canals, branches, and deltas). After eruption, the tooth...

A defining feature of dentitions in modern sharks and rays is the regulated pattern order that generates multiple replacement teeth. These are arranged in labio-lingual files of replacement teeth that form in sequential time order both along the jaw and within successively initiated teeth in a deep dental lamina. Two distinct adult dentitions have...

Placoderms (Devonian fossil fishes) are resolved phylogenetically to the base of jawed vertebrates and provide important evidence for evolutionary origins of teeth, particularly with respect to the Arthrodira. The arthrodires represent a derived group of placoderms; the dentition of other more primitive placoderms such as the acanthothoracids is le...

Palaeospondylus gunni Traquair, 1890 is an enigmatic Devonian vertebrate whose taxonomic affinities have been debated since it was first described. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of...

This is an update on our article " Jawed vertebrate dentitions – when did teeth evolve " which appeared as a review for infocus 42, June 2016 but since then two important papers have just been published on the topic we choose to headline here.

The squaliform sharks represent one of the most speciose shark clades. Many adult squaliforms have blade-like teeth, either on both jaws or restricted to the lower jaw, forming a continuous, serrated blade along the jaw margin. These teeth are replaced as a single unit and successor teeth lack the alternate arrangement present in other elasmobranch...

Summary Our research is concerned with the question of tooth origins and the relationship of teeth with the body scales, of both modern and extinct fishes. To unravel the evolutionary steps that led to tooth origins we focus our attention on both fossil and living fishes with potential ancestral dental characters. Our emphasis is on the organisatio...

The description of a partial but well preserved head of the sclerorhynchid batoid Sclerorhynchus atavus Woodward 1889 gave the first clear indication of the presence of a puzzling group of extinct rostrum-bearing rays that resembled both the Pristidae (rays) and the Pristophoridae (sharks). Despite recognizing similarities and differences to these...

In classical theory, teeth of vertebrate dentitions evolved from co-option of external skin denticles into the oral cavity. This hypothesis predicts that ordered tooth arrangement and regulated replacement in the oral dentition were also derived from skin denticles. The fossil batoid ray Schizorhiza stromeri (Chondrichthyes; Cretaceous) provides a...

Chondrichthyans possess both true teeth within their mouth and tooth-like denticles on their skin, both outside and inside the mouth. Understanding the relationships between teeth and denticles is fundamental to the interpretation of the origins of teeth within the gnathostomes. Superficially tooth-like structures on the body surface of sharks and...

A well-known characteristic of chondrichthyans (e.g. sharks, rays) is their covering of external skin denticles (placoid scales), but less well understood is the wide morphological diversity that these skin denticles can show. Some of the more unusual of these are the tooth-like structures associated with the elongate cartilaginous rostrum ‘saw’ in...

Origins of the vertebrate dentition, as a patterned, functional unit associated with the jaws, remain contentious. Hypotheses suggest dentitions evolved from external placoid scales, or alternatively, from denticles within the oropharyngeal cavity, with no input from external dermal structures. The latter hypothesis suggests that oral dentitions an...

Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of Polyodon...

Shark and ray (elasmobranch) dentitions are well known for their multiple generations of teeth, with isolated teeth being common in the fossil record. However, how the diverse dentitions characteristic of elasmobranchs form is still poorly understood. Data on the development and maintenance of the dental patterning in this major vertebrate group wi...

Ray-finned fishes (Actinopterygii) are the dominant vertebrate group today (+30 000 species, predominantly teleosts), with great morphological diversity, including their dentitions. How dental morphological variation evolved is best addressed by considering a range of taxa across actinopterygian phylogeny; here we examine the dentition of Polyodon...

The outer armour of fossil jawless fishes (Heterostraci) is, predominantly, a bone with a superficial ornament of dentine tubercles surrounded by pores leading to flask-shaped crypts (ampullae). However, despite the extensive bone present in these early dermal skeletons, damage was repaired almost exclusively with dentine. Consolidation of bone, by...

Previously described scale morphotypes of Silurian thelodonts, constrained by their representation as isolated dermal denticles are reassessed to provide a more robust character basis for their inclusion in future phylogenetic studies. As relatively common microfossils, thelodonts are important biostratigraphical markers, but their interrelationshi...

Teleost fishes comprise approximately half of all living vertebrates. The extreme range of diversity in teleosts is remarkable, especially, extensive morphological variation in their jaws and dentition. Some of the most unusual dentitions are found among members of the highly derived teleost order Tetraodontiformes, which includes triggerfishes, bo...

Cartilaginous vertebrate skeletons leave few records as fossils, unless mineralized. Here, we report outstanding preservation of early stages of cartilage differentiation, present in the Devonian vertebrate Palaeospondylus gunni. In large specimens of Palaeospondylus, enlarged, hypertrophic cell spaces (lacunae) are dominant in the cartilage matrix...

The mode of tooth development displayed in Chondrichthyans (sharks, rays and holocephalans), one of frequent tooth replacement, was possible once a dental lamina had evolved, and since 1982 this has been known as the odontode regulation theory after Reif. Today, Reif's concepts need to be transformed into those of modern biology, the crosstalk betw...

Classically the oral dentition with teeth regulated into a successional iterative order was thought to have evolved from the superficial skin denticles migrating into the mouth at the stage when jaws evolved. The canonical view is that the initiation of a pattern order for teeth at the mouth margin required development of a sub-epithelial, permanen...

Lungfi sh have a long evolutionary history, fi rst appearing in the Early Devonian, with three genera extant. Lungfi sh dentitions were particularly diverse and have been a focus of study for many years. Although diverse, all dentitions can be derived from a toothplated dentition, where components of this dentition, in terms of tooth structures and...

The bearing that agnathans have on the origin of jawed vertebrates is one of the great unsolved problems in vertebrate phylogeny. Here we propose a mechanism for the evolution of jaws in vertebrates based on a combination of evidence from the fossil record and from experimental developmental biology. In chick embryos, osteogenesis can be evoked exp...

Palaeospondylus gunni (Devonian, Scotland) is an enigmatic vertebrate, assigned to various jawless and jawed groups since its original description. New sections through the whole body allow description of a novel skeletal tissue for Palaeospondylus, comprising the entire skeleton. This tissue is mineralized cartilage and is characterized by large c...

An investigation with the scanning electron microscope into the microstructure of the surface layer covering the oral teeth of Latimeria chalumnae has shown this tissue to be enamel of the type found in amphibians, reptiles and mammals. It is not comparable with enameloid, cuticular enamel or terminal membrane enamel as described in scanning electr...

Scales from four specimens of Latimeria chalumnae were examined in a dissecting microscope and then X‐rayed. Some were demineralized and prepared for routine histology. Others were cleared in cedarwood oil. Ground sections of plastic embedded scales were micro‐radiographed and electronmicrographs made of araldite embedded frozen scales. Correspondi...

This study considers stem cells for odontogenic capability in biological tooth renewal in the broad context of gnathostome dentitions and the derivation of them from oral epithelium. The location of the developmental site and cell dynamics of the dental lamina are parameters of a possible source for odontogenic epithelial stem cells, but the phylog...

For a dentition representing the most basal extant gnathostomes, that of the shark can provide us with key insights into the evolution of vertebrate dentitions. To detail the pattern of odontogenesis, we have profiled the expression of sonic hedgehog, a key regulator of tooth induction. We find in the catshark (Scyliorhinus canicula) that intense s...

Since the 1980s, a renewed understanding of molecular development has afforded an unprecedented level of knowledge of the mechanisms by which phenotype in animals and plants has evolved. In this volume, top scientists in these fields provide perspectives on how molecular data in biology help to elucidate key questions in estimating paleontological...

We report a temporal order of tooth addition in the Australian lungfish where timing of tooth induction is sequential in the same pattern as osteichthyans along the lower jaw. The order of tooth initiation in Neoceratodus starts from the midline tooth, together with left and right ones at jaw position 2, followed by 3 and then 1. This is the patter...

Experimental evidence that the neural crest participates in tooth development in any osteichthyan fish has so far been lacking. Using vital dye cell-lineage tracking, we demonstrate that trigeminal stream neural crest cells contribute to the dental papilla of developing teeth in the Australian lungfish. Trigeminal neural crest cells labeled before...

A new actinopterygian fish Yaomoshania minutosquama gen. & sp. nov., from the Upper Permian of the Dzungaria [Junggar] Basin in China is described. The material consists of two very fragmentary specimens showing almost exclusively scale rows. The arrangement of the scale rows of the holotype resembles the reversion lines of acanthodian caudal fins...

Regular scale patterning, restricted to the caudalmost tail and organized into two opposing rows on each side of the tail, is observed in few chondrichthyans. These evenly spaced scales, in dorsal and ventral rows, develop in an iterative sequence from the caudal tip, either side of the notochord. They are subsequently lost as a scattered pattern o...

In two species of Heterodontus, H. portusjacksoni and H. galeatus, the first scales to develop form two opposing rows along the caudal fin axis on both the left and right sides of the fin. The opposing rows originate from an initial scale located on either side of the posterior tip of the caudal fin, with subsequent scales erupting in a posterior t...

Repeated tooth initiation occurs often in nonmammalian vertebrates (polyphyodontism), recurrently linked with tooth shedding and in a definite order of succession. Regulation of this process has not been genetically defined and it is unclear if the mechanisms for constant generation of replacement teeth (secondary dentition) are similar to those us...

Although the lungfish (Dipnoi) belong within the Osteichthyes, their dentitions are radically different from other osteichthyans. Lungfish dentitions also show a uniquely high structural disparity during the early evolution of the group, partly owing to the independent variation of odontogenic and odontoclastic processes that are tightly and stereo...

The rainbow trout (Oncorhynchus mykiss) as a developmental model surpasses both zebrafish and mouse for a more widespread distribution of teeth in the oro-pharynx as the basis for general vertebrate odontogenesis, one in which replacement is an essential requirement. Studies on the rainbow trout have led to the identification of the initial sequent...

This introduction to new patterning theories for the vertebrate dentition outlines the historical concepts to explain graded sequences in tooth shape in mammals (incisors, canines, premolars, molars) which change in evolution in a linked manner, constant for each region. The classic developmental models for shape regulation, known as the 'regional...

The rainbow trout (Oncorhynchus mykiss) as a developmental model surpasses both zebrafish and mouse for a more widespread distribution of teeth in the oro-pharynx as the basis for general vertebrate odontogenesis, one in which replacement is an essential requirement. Studies on the rainbow trout have led to the identification of the initial sequent...