Dermal Denticles Research Articles

What came first, the shark or the egg? Discovery of a new species of deepwater shark by investigation of egg case morphology.

Apristurus ovicorrugatus, a new species of deepwater catshark, is described from northwestern Australia. Unique egg cases belonging to an unknown species of Apristurus prompted a more detailed investigation of Apristurus specimens off northwestern Australia. One specimen previously identified as A. sinensis collected off Dampier Archipelago was found gravid with a single egg case. Removal of this egg case confirmed that this species was responsible for producing the unique egg cases previously recorded. The egg cases of this species have strong T-shaped longitudinal ridges on the dorsal and ventral surfaces which are unique in the genus Apristurus. The ridges most closely resemble those present in Bythaelurus canescens from South America, but are larger and always T-shaped. The holotype is closest morphologically to A. sinensis but differs in having a medium brown buccal cavity (vs. jet black), ridged egg cases (vs. smooth egg cases), fewer intestinal spiral valve turns and larger pectoral fins. The holotype is also similar, and closest on a molecular level, to A. nakayai with which it shares a unique synapomorphic character, the white shiny iris (apomorphic within the genus). A late-term embryo removed from an egg case superficially resembled the holotype except in having two parallel rows of enlarged dermal denticles on the dorsolateral predorsal surface. Recent nomenclatural changes to the genera Apristurus and Pentanchus are discussed and challenged. This study highlights the important contribution that egg case morphology has on oviparous elasmobranch taxonomy.

Untangling the systematic dilemma behind the roughskin spurdog Cirrhigaleus asper (Merrett, 1973) (Chondrichthyes: Squaliformes), with phylogeny of Squalidae and a key to Cirrhigaleus species.

Cirrhigaleus comprises a small genus of rare barbel-bearing dogfish sharks with distributions in limited regions of all oceans. Generic validity and taxonomic status of some species are upon controversies by morphological and molecular evidence that often suggest reallocation of Cirrhigaleus species into the genus Squalus. Particularly, the roughskin spurdog C. asper exhibits intermediary morphological characteristics within Squalidae that requires clarification. In the present study, a phylogenetic approach was undertaken to test the correct generic placement of C. asper using novel and revised morphological characters. We performed maximum parsimony analysis of 51 morphological characters of the internal (e.g., neurocranium, clasper cartilages, pectoral and pelvic girdles) and external anatomy applied to 13 terminal taxa. Cirrhigaleus represents a valid genus and it is supported by eight synapomorphies: high number of monospondylous vertebrae; medial nasal lobe supported by fleshy core and innervated by the buccopharyngeal branch of the facial nerve; neurocranium with greatest width across nasal capsules; one facet and one condyle in the puboischiadic bar for articulating with the basipterygium; two intermediate segments between the basipterygium of the pelvic fin and the axial cartilage of the claspers; five terminal clasper cartilages; and posterior medial process of the puboischiadic bar absent. Cirrhigaleus asper is sister-species to a small clade comprising C. barbifer and C. australis which is supported by one synapomorphy, presence of conspicuous cusplets in the dermal denticles. Cirrhigaleus barbifer, C. asper and C. australis are redescribed herein and the neotype of C. barbifer is designated. A key to Cirrhigaleus species is also given and the inner relationships within Squalus is tentatively discussed.

Stingray epidermal microbiomes are species-specific with local adaptations.

Marine host-associated microbiomes are affected by a combination of species-specific (e.g., host ancestry, genotype) and habitat-specific features (e.g., environmental physiochemistry and microbial biogeography). The stingray epidermis provides a gradient of characteristics from high dermal denticles coverage with low mucus to reduce dermal denticles and high levels of mucus. Here we investigate the effects of host phylogeny and habitat by comparing the epidermal microbiomes of Myliobatis californica (bat rays) with a mucus rich epidermis, and Urobatis halleri (round rays) with a mucus reduced epidermis from two locations, Los Angeles and San Diego, California (a 150 km distance). We found that host microbiomes are species-specific and distinct from the water column, however composition of M. californica microbiomes showed more variability between individuals compared to U. halleri. The variability in the microbiome of M. californica caused the microbial taxa to be similar across locations, while U. halleri microbiomes were distinct across locations. Despite taxonomic differences, Shannon diversity is the same across the two locations in U. halleri microbiomes suggesting the taxonomic composition are locally adapted, but diversity is maintained by the host. Myliobatis californica and U. halleri microbiomes maintain functional similarity across Los Angeles and San Diego and each ray showed several unique functional genes. Myliobatis californica has a greater relative abundance of RNA Polymerase III-like genes in the microbiome than U. halleri, suggesting specific adaptations to a heavy mucus environment. Construction of Metagenome Assembled Genomes (MAGs) identified novel microbial species within Rhodobacteraceae, Moraxellaceae, Caulobacteraceae, Alcanivoracaceae and Gammaproteobacteria. All MAGs had a high abundance of active RNA processing genes, heavy metal, and antibiotic resistant genes, suggesting the stingray mucus supports high microbial growth rates, which may drive high levels of competition within the microbiomes increasing the antimicrobial properties of the microbes.

The first Late Permian fish fossils from Leszczyna quarry in South-West Poland

ABSTRACTPermian fishes and their isolated microremains are known from many localities in the Zechstein Basin. However, up to date the vertebrates have never been revealed in the southeasternmost part of this ancient sea. The new material consists of euselachian-type dermal denticles,?Listracanthus sp. dermal denticle,?Omanoselache sp. tooth, actinopterygian scales and actinopterygian teeth. Here, the detailed study of euselachian and actinopterygian remains, their stratigraphic distribution and geographical contexts is presented. Based on the qualitative analysis of teeth shapes several ecomorphotypes were described as well as the probable dietary preferences of fishes were reconstructed. These finds confirmed existence of small predators who fed on soft bodied prey as well as durophagous forms which were feeding on small shelly crustaceans or molluscs. The analysis of stratigraphic distribution of microremains, and their comparison with neighbouring sections revealed a spatially correlatable trend in increasing abundance of fishes in the more clayey parts of sections, interpreted to be positively associated with a sea level transgression event.

Using Fish Remains to Trace Dynamic Exchanges Between Ecology and Economy in Fiji

Island nations in the developing world are some of the communities most at-risk to the effects of climate change and are under increasing pressure from globalized seafood markets. Indigenous Fijians have a stark understanding of environmental change because of their economic and dietary reliance on marine resources, including shark fisheries and tourism. Sharks are important apex predators with deep cultural significance in Fiji and they are thus useful species to focus on when investigating historical ecology. However, they are difficult to study; sharks have cartilaginous skeletons, making full body fossils rare, and their behavior can make them difficult to survey with traditional methods. Sharks are also covered in dermal denticles which they shed throughout their lives and which compose some of the most extensive and oldest fossil types. All fish, including sharks, also shed their teeth, and together these microfossils are called ichthyoliths. Scientists in the Caribbean have developed innovative techniques to use ichthyoliths to illuminate the importance of parrotfish to coral reef ecology and trace historical and pre-anthropogenic shark populations. However, this microfossil approach has not yet reached Fiji. We developed a trait-based character coding scheme to describe denticle morphology based on both modern denticles and fossil denticles and discuss our work to expand current denticle reference collections. When combined with ecological factors, morphological analysis can identify temporal periods and spatial regions of importance in both modern and paleo-ocean ecosystem dynamics and aid historical ecologists in describing shark communities of the past. We are embarking on a research project to collect cores from Fiji to examine parrotfish and shark ecology through time. Here we summarize the methods we will use and how we have tailored them to our study region and invite input from the conservation paleobiology community on our study design.

Reconstructing Millennial-Scale Variability in Reef Shark Communities Across The Isthmus of Panama

Shark populations have declined over the last half century, but the patterns of change vary across space. Long-term records of shark abundance are limited, making it challenging to determine how local environmental conditions influence pre-exploitation shark baselines and their susceptibility to human impacts. We use shark scales (dermal denticles) preserved in coral reef sediments to reconstruct shark communities during the mid-Holocene and today across the Isthmus of Panama. We interpret these data alongside records of primary productivity, habitat, and fish abundance to explore energy flow to higher trophic levels on each coast. The Tropical Eastern Pacific is a productive system driven by seasonal upwelling with a long history of shark exploitation. The Caribbean coast, on the other hand, is oligotrophic and environmentally stable, with lower rates of harvesting. We find that denticle accumulation rates, a proxy for shark abundance, are an order of magnitude greater in Pacific Panama (Gulf of Panama) than in Caribbean Panama (Bocas del Toro). Primary productivity and fish abundance are also higher in Pacific Panama, helping to support these large predator populations. Denticle accumulation rates declined by 71% since the mid-Holocene in Caribbean Panama, including a selective loss of pelagic sharks. In contrast, modern denticle accumulation rates in Pacific Panama are comparable to their range of variability during the mid-Holocene, and the composition of denticle assemblages remained similar through time—suggesting that sharks in the Gulf of Panama have persisted despite intensive fishing. We postulate that the region’s high productivity might underlie its high shark abundance and apparent resilience by increasing available resources for predators. Our findings shed light on the role of energy in shaping natural variability in shark baselines and recovery potential. They also highlight the importance of incorporating oceanographic context into shark management.

INVESTIGATION OF REDUCING PRESSURE DROP BY PATTERNING DERMAL DENTICLES (SHARK SKIN) ON THE PLATE SURFACE OF COMPACT PLATE HEAT EXCHANGER

Heat transfer can be realized by increasing the surface area with designs in various geometries and sizes in a compact plate heat exchanger (PHE). However, designs with low volume and high heat transfer area cause high pressure drop. In order to overcome this problem, this study examines the pressure drop of a shark-skin-patterned PHE designed using biomimicry approach. The structure of shark skin consists of an array of pulpolites called dermal denticles. This study is carried out for the first time, taking into account the friction-reducing effect of such structure on nonsmooth surfaces. A dermal denticles-patterned PHE is designed for the first time. The numerical results of the dermal denticles-patterned PHE are compared with those of a standard chevron-type PHE. The results of this study show that the heat transfer rate of the dermal denticles-patterned PHE increases by 50% compared to the standard chevron-type PHE. A 72.5% decrease is provided from the pressure drop of the standard chevron-type PHE. The mechanism that causes the reduced pressure drop is discussed in detail in the article.

Teeth outside the mouth: The evolution and development of shark denticles.

Vertebrate skin appendages are incredibly diverse. This diversity, which includes structures such as scales, feathers, and hair, likely evolved from a shared anatomical placode, suggesting broad conservation of the early development of these organs. Some of the earliest known skin appendages are dentine and enamel-rich tooth-like structures, collectively known as odontodes. These appendages evolved over 450 million years ago. Elasmobranchs (sharks, skates, and rays) have retained these ancient skin appendages in the form of both dermal denticles (scales) and oral teeth. Despite our knowledge of denticle function in adult sharks, our understanding of their development and morphogenesis is less advanced. Even though denticles in sharks appear structurally similar to oral teeth, there has been limited data directly comparing the molecular development of these distinct elements. Here, we chart the development of denticles in the embryonic small-spotted catshark (Scyliorhinus canicula) and characterize the expression of conserved genes known to mediate dental development. We find that shark denticle development shares a vast gene expression signature with developing teeth. However, denticles have restricted regenerative potential, as they lack a sox2+ stem cell niche associated with the maintenance of a dental lamina, an essential requirement for continuous tooth replacement. We compare developing denticles to other skin appendages, including both sensory skin appendages and avian feathers. This reveals that denticles are not only tooth-like in structure, but that they also share an ancient developmental gene set that is likely common to all epidermal appendages.

Fish remains from the Rhaetian (Late Triassic) of Winterswijk, the Netherlands (Pisces: Chondrichthyes and Actinopterygii)

Abstract Chondrichthyan and actinopterygian fish remains from Rhaetian (c. 208.05–201.36 Ma) or perhaps Late Norian deposits in the Winterswijk quarry are described. The most abundant taxon is the actinopterygian Gyrolepis albertii, followed by the chondrichthyan Lissodus minimus. Furthermore, the palaeopterygian actinopterygians Saurichthys longidens and Birgeria acuminata, and some teeth of neopterygians Sargodon tomicus, ‘Lepidotes’ sp. and indeterminate pycnodontiforms are recorded in addition to the chondrichthyans Rhomphaiodon minor, Parascylloides turnerae and some ‘Hybodus’ cf. cuspidatus (senior synonym of H. cloacinus). Chondrichthyan dermal denticles, actinopterygian scales and gill rakers, tooth plates, and some fish bones were also found. There is considerable faunal resemblance to the various localities from the Rhaetian of the British Penarth Group, although it depends on the location as to whether chondrichthyans or actinopterygians prevail in the samples. On average, there are more chondrichthyan teeth present in the British samples than actinopterygian teeth, which is opposite to the situation in Winterswijk. That might be explained by different ecological circumstances, such as lower oxygen levels in bottom waters in Winterswijk and freshwater input and/or changes in salinity in the UK.

Encountering the morphological and molecular complexity in the bramble shark Echinorhinus cf. E. brucus (Bonnaterre 1788) from the Oman Sea

Abstract This is the first simultaneous morphological and barcoding characterization with the cytochrome c oxidase subunit I (COI) of the bramble shark Echinorhinus from the coast of Oman. The morphology of the specimen was consistent with previous records of Echinorhinus from the Gulf of Oman and the Arabian Sea (Northwestern Indian Ocean). However, the new COI haplotype clustered together with homologous sequences of specimens from India. The specimen from Oman distinguished morphologically and genetically from an E. brucus from the Western Atlantic Ocean on the shape and size of the dermal denticles, the proportions of twelve morphometric measurements (differences ⩾3%) and the genetic p-distance = 3.8% of the COI fragment. The haplotype reported here increases the genetic diversity in genus Echinorhinus in the Northwest Indian Ocean, demonstrates conspecificity between specimens from Oman and Echinorhinus cf. E. brucus distributed in India and extends its range of distribution. The limited morphological and molecular data available constrained assigning our specimen to other than Echinorhinus cf. E. brucus (Bonnaterrez, 1788). Our findings highlight the urgent need of morphological review, redescription and the assignment of a neotype in order to guarantee accurate species identification and thus effective conservation measures for these deep-sea sharks. The existence of a third living species in the genus is briefly discussed.

New record of the prickly shark Echinorhinus cookei (Pietschmann, 1928) and evidence of scavenging by the coyote Canis latrans (Say, 1823) in Bahia de Los Angeles, Baja California, Mexico

Echinorhinus cookei is a rare, large, demersal, deep-sea species of shark inhabitant of the Pacific Ocean basin. A sub-adult female with a total length of 262.7 cm was found naturally stranded in 2021 at Bahia de Los Angeles, Baja California, Central Gulf of California. It presents two spineless dorsal fins closer to the pelvic fins, large star-shaped dermal denticles, and distally oriented multi-cusplet cutting-type teeth. Along the shark, a peninsular coyote Canis latrans peninsulae was observed scavenging on the shark carcass. This study documents the first record of E. cookei in the Bahia de Los Angeles area and the first record of scavenging by the coyote C. latrans on any echinorhiniform shark to date.

Novel Method for the Extraction of DNA from Lamniformes Tooth and Denticle Enamel Suitable for PCR

Extraction of high-quality genomic DNA from Lamniformes tooth fragment and dermal denticle enamel is discussed as a method of identifying individual sharks. We describe a procedure that permits isolation of genomic DNA of satisfactory size and quality for PCR analysis, as well as for most routine cloning applications. This method should allow for the non-invasive collection of genomic samples from Lamniformes.

Shark skin biomimetic surface modification for plates: influence on free vibration response

Denticle microstructures in shark skin have intrigued researchers since they can be prospective for various marine applications due to their inherent properties which help in reducing drag as well as do not allow barnacles to form on its surface. However, any such alterations to create surface rivulets will invariably lead to changes in mass and stiffness, and thereby natural frequencies. Subsequently, the dynamic response will also be influenced as these hydrodynamic phenomena are strongly dependent on the natural frequencies. Therefore, in this work, an investigation of the effect of shark skin type biomimetic surface modifications on the free vibration response is investigated. The free vibration response of plates with shark skin is computed first using a high-fidelity numerical simulation in a commercial finite element package ABAQUS and then compared against a simplified semi-analytical model proposed herein. Results from both these methods agreed quite well. It is observed that shark skin denticles significantly influence the natural frequency without altering its mode shapes. It appears that adding shark skin like dermal denticles on the surface of a bare plate as an appendage helps in reducing the natural frequencies in each mode. The study also reveals that the reduction in the spacing between denticles reduces natural frequency even further. Therefore, the effect of these wettability altercations on free vibration response should be known apriori for efficient design.

Redescription and anatomical investigation of Schroederichthys maculatus Springer, 1966 and S. saurisqualus Soto, 2001 with comments on their systematics (Chondrichthyes: Carcharhiniformes: Atelomycteridae)

Schroederichthys maculatus and S. saurisqualus together with S. tenuis present an elongated postpelvic trunk region and are usually referred as the neotenic species group of the genus Schroederichthys. The original morphological description of the two former species was mainly focused on external morphology and detailed information on anatomical structures such as neurocranium and teeth are lacking. This study aims, therefore, to present further information on external morphology, teeth and dermal denticles and to reappraise and illustrate skeletal structures of Schroederichthys maculatus and S. saurisqualus. Ethanol-preserved specimens of both species were measured and dissected for the examination of internal anatomical structures, such as neurocranium, teeth, dermal denticles and visceral arches. Three new tooth measurements are proposed herein. Neurocranial measurements, disposition of orbital foramina and tooth characters vary among neotenic species of Schroederichthys and should be included in future cladistic analyses. A detailed anatomical investigation of S. bivius and S. chilensis is also recommended in order to shed light on the interrelationships within the genus.

Phage Diving: An Exploration of the Carcharhinid Shark Epidermal Virome.

The epidermal microbiome is a critical element of marine organismal immunity, but the epidermal virome of marine organisms remains largely unexplored. The epidermis of sharks represents a unique viromic ecosystem. Sharks secrete a thin layer of mucus which harbors a diverse microbiome, while their hydrodynamic dermal denticles simultaneously repel environmental microbes. Here, we sampled the virome from the epidermis of three shark species in the family Carcharhinidae: the genetically and morphologically similar Carcharhinus obscurus (n = 6) and Carcharhinus galapagensis (n = 10) and the outgroup Galeocerdo cuvier (n = 15). Virome taxonomy was characterized using shotgun metagenomics and compared with a suite of multivariate analyses. All three sharks retain species-specific but highly similar epidermal viromes dominated by uncharacterized bacteriophages which vary slightly in proportional abundance within and among shark species. Intraspecific variation was lower among C. galapagensis than among C. obscurus and G. cuvier. Using both the annotated and unannotated reads, we were able to determine that the Carcharhinus galapagensis viromes were more similar to that of G. cuvier than they were to that of C. obscurus, suggesting that behavioral niche may be a more prominent driver of virome than host phylogeny.

The first southern hemisphere occurrence of the extinct Cretaceous sclerorhynchoid sawfish Ptychotrygon (Chondrichthyes, Batoidea), with a review of Ptychotrygon taxonomy

ABSTRACT A new extinct sclerorhynchoid sawfish, Ptychotrygon ameghinorum sp. nov., is presented here based on abundant isolated teeth and some dermal denticles, which were recovered from the Mata Amarilla Formation, belonging to the lower Upper Cretaceous of the Santa Cruz Province in the Austral Basin of Patagonia, Argentina. This new species is the first Ptychotrygon occurrence in the southern hemisphere, which so far only has been reported from northern hemisphere deposits (Europe, North Africa, and North America). The presence of P. ameghinorum sp. nov. in these southern high-latitude deposits of Patagonia, Argentina, extends the geographic range of Ptychotrygon considerably southwards. This distribution pattern in the “middle” Cretaceous seems to correlate with the South Atlantic opening at the end of the Albian. The presence of lateral cephalic dermal denticles and the simultaneous absence of rostral denticles in the abundant fossil material support the view that Ptychotrygon did not develop such rostral structures. A reinvestigation of all known species assigned to Ptychotrygon reveals that P. ellae is a junior synonym of P. boothi, P. benningensis belongs to Texatrygon, P. rugosum belongs to Asflapristis, and P. clementsi represents an unidentifiable species (Ptychotrygon? sp.). The stratigraphic distribution demonstrates that Ptychotrygon might have originated in the Albian in south-western Europe and subsequently dispersed to obtain its widest distribution during the Cenomanian. In the Coniacian, a steep diversity decline is recognizable with a subsequent distribution shift from Europe to North America.

Connected Microscopy to Characterise the Dermal Denticle of Raja clavata, the Thornback Ray

Connected Microscopy to Characterise the Dermal Denticle of <i>Raja clavata</i>, the Thornback Ray

Morphological pattern of the dermal denticles of the Southern sawtail catshark Galeus mincaronei Soto, 2001.

Dermal denticles cover the skin of sharks for protection and may have additional functions, depending on the environment. The aim of the present study was to analyze the morphological pattern of dermal denticles across the body of the poorly known deep-water catshark Galeus mincaronei, which is endemic to Southern Brazil. Additionally, we aimed to identify differences between sexes and stages of sexual maturity. For this purpose, we analyzed patches of eight skin samples from body regions, that is, the head, body, and tail. Dermal denticles were imaged using scanning electron microscopy. Measurements of crown morphological variations (length and width) and density of dermal denticles were performed. Nine characters of dermal denticle morphology were selected to describe a morphological pattern using principal component analysis (PCA). The first PCA axis explained 45.2% of the variation, the second explained 33%, and the third explained 14.3%, together explaining 92.5% of the total variation in denticle morphology. We identified three groups of dermal denticle crown morphologies and their possible functions. The first was composed of nostril and snout denticles, which might suggest abrasion strength functions; the second was composed of most body denticles, such as those in the cranium, on the left side of the body, and on the pectoral, dorsal, and caudal fins, which might be related to generalized functions; and the third was composed of only caudal crest denticles, which might indicate defense functions with hydrodynamic properties in G. mincaronei. Likewise, our results reveal variations in dermal denticle morphology and arrangement along the three maturity stages considered in both sexes. Similarly, sexual dimorphism in the crown width and morphology of dermal denticles was observed in developing and mature individuals. Our results are the first to reveal the morphological variation of dermal denticles in relation to function, sex, and ontogeny of individual G. mincaronei.

Morphological study of the oral denticles of the porbeagle shark Lamna nasus.

Oral denticles of sharks are composed by a crown, dentine covered by a layer of enameloid and pulp cavity, the same structure of the dermal denticles found across the body surface of most elasmobranchs. In addition, oral papillae and taste buds are distributed among denticles within the oropharyngeal cavity, playing a fundamental role for tasting as part of the chemosensory system of fishes. Scanning electron microscopy (SEM) has been employed as an important tool for the study of dermal denticles and other structures, as well as histology and more recently computed tomography(CT) scan analysis. Herein, the authors used two methods for the study of the morphology of the oropharyngeal cavity of Lamna nasus (Lamniformes), an oceanic and pelagic shark: SEM and CT scan. The general morphology of oral denticles studied herein is related to abrasion strength as they are diamond-shaped, lack lateral cusps and have less pronounced ridges. In addition, smooth ridges and broad rounded denticles could be related to prevent abrasion during food consumption and manipulation. Oral papillae had a round shape and were observed only under SEM. The densities of papillae were estimated in 100 per cm2 , whereas denticles were 1760 and 1230 cm2 over the dorsal and ventral regions, respectively. The high numbers of denticles are inversely proportional to papillae density; denticles seem to restrict papillae distribution. Regarding the differences between methodologies, under SEM, only the crown was visualized, as well the papillae, allowing the estimation of size and density of both structures. Nonetheless, under CT scan, the whole components of denticles were clearly visualized: different views of the crown, peduncle, basal plate, and pulp cavity. On the contrary, oral papillae were not visualized under CT due to the tissue preparation. Furthermore, both methods are complementary and were important to extract as much information as possible from denticles and papillae.

Complex enameloid microstructure of †Ischyrhiza mira rostral denticles.

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.