Dermal Bones Research Articles

The development of cephalic armor in the tokay gecko (Squamata: Gekkonidae: Gekko gecko).

Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap-footed lizards) only known to occur in three genera: Geckolepis, Gekko, and Tarentola. The Tokay gecko (Gekko gecko LINNAEUS 1758) is among the best-studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well-known. Likewise, a comparative survey of additional species within the broader Gekko clade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens of G. gecko, using X-rays and high-resolution computed tomography for visualizing and quantifying the dermal armor in situ. Results from this survey confirm the presence of osteoderms in a second species within this genus, Gekko reevesii GRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon, G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found that G. gecko and other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms.

A new onychodont (Osteichthyes; Sarcopterygii) from the Middle Devonian of Morocco and its bearing on early osteichthyan evolution

A new onychodont sarcopterygian is described from the Middle Devonian (Eifelian) of Morocco. Selenodus aquesbiae gen. et sp. nov. is characterized by a unique suite of traits among onychodonts such as a large maxilla with a rounded posterior expansion and a straight ventral margin, the presence of a single supraorbital, and a reduced opercular series. It also displays certain features commonly found in onychodontids and early sarcopterygians, like a lateral rostral contacting the orbit through a narrow posterodorsal projection, numerous sclerotic plates surrounding the orbit, the occurrence of an accessory row of small denticles labially lining the single row of teeth from the upper and lower jaws, a prearticular ornamented with small rounded tubercules, the postotic lateral line canal passing through the supratemporal, tabular and lateral extrascapular bones of the skull roof, and dermal bones and rounded scales ornamented by small dentine tubercules capped with enamel. All the fossil remains belong to a single individual representing a relatively large fish (around 1 m of estimated length based on the skull dimensions) for which the snout, cheek, and skull roof have been partially reconstructed. The well-preserved material comprises mainly the dermocranium but two branchial elements are known, adding to our knowledge of early osteichthyan endoskeleton. A phylogenetic analysis places Selenodus in an unresolved polytomy among onychodonts and coelacanths, enabling discussion of evolutionary scenarios and character combinations among early osteichthyans. The close relationship between onychodonts and actinistians is firmly established and suggests that all onychodont taxa are stem coelacanths. Selenodus represents the first occurrence of onychodonts from Africa and furnishes key information not only on onychodont morphology and interrelationships but also on their palaeobiogeographical distribution and Devonian faunal affinities between Euramerica and Gondwana.http://zoobank.org/urn:lsid:zoobank.org:pub:3FEB765B-E203-4015-BB48-20B108509F3B

Retention of fish-like odontode overgrowth in Permian tetrapod dentition supports outside-in theory of tooth origins.

Teeth are often thought of as structures that line the margins of the mouth; however, tooth-like structures called odontodes are commonly found on the dermal bones of many Palaeozoic vertebrates including early jawless fishes. 'Odontode' is a generalized term for all tooth-like dentine structures that have homologous tissues and development. This definition includes true teeth and the odontodes of early 'fishes', which have been recently examined to gain new insights into the still unresolved origin of teeth. Two leading hypotheses are frequently referenced in this debate: the 'outside-in' hypothesis, which posits that dermal odontodes evolutionarily migrate into the oral cavity, and the 'inside-out' hypothesis, which posits that teeth originated in the oropharyngeal cavity and then moved outwards into the oral cavity. Here, we show that, unlike the well-known one-to-one replacement patterns of marginal dentition, the palatal dentition of the early Permian tetrapods, including the dissorophoid amphibian Cacops and the early reptile Captorhinus, is overgrown by a new layer of bone to which the newest teeth are then attached. This same overgrowth pattern has been well documented in dermal and oral odontodes (i.e. teeth) of early fishes. We propose that this pattern represents the primitive condition for vertebrates and may even predate the origin of jaws. Therefore, this pattern crosses the fish-tetrapod transition, and the retention of this ancestral pattern in the palatal dentition of early terrestrial tetrapods provides strong support for the 'outside-in' hypothesis of tooth origins.

Cranial osteology of the Middle Jurassic (Callovian) Martillichthys renwickae (Neopterygii, Pachycormiformes) with comments on the evolution and ecology of edentulous pachycormiforms

AbstractOur understanding of the ecology and phylogenetic relationships of Pachycormiformes, a group of Mesozoic stem teleosts including the iconic Leedsichthys, has often been hindered by a lack of comprehensive morphological information. Micro‐CT scanning of an articulated, although flattened, cranium of the edentulous Martillichthys renwickae from the Middle Jurassic (Callovian) Oxford Clay of the UK reveals previously unknown internal details of the most complete suspension‐feeding pachycormiform skull known, including the palate, braincase and branchial skeleton. The latter preserves gill rakers with elongate, pointed projections similar to those of Asthenocormus, in contrast to the finer fimbriations associated with Leedsichthys. We also reinterpret some previously described features, including dermal bone patterns of the snout, skull roof and lower jaw, and the morphology of the ventral hyoid arch. These new anatomical data reinforce the phylogenetic placement of Martillichthys as part of the Jurassic clade of edentulous pachycormiforms. The elongate skull geometry of these Jurassic taxa is strikingly similar to that of Ohmdenia, the sister taxon to edentulous pachycormiforms, but contrasts sharply with the morphology of the Late Cretaceous edentulous pachycormiform Bonnerichthys, raising questions over the phylogenetic relationships among these taxa. Most significantly, Martillichthys shows specialized characters with a restricted phylogenetic distribution among suspension‐feeding pachycormiforms, including the distinctive gill rakers and a greatly extended occipital stalk. Our analysis of Martillichthys supports past interpretations of a close relationship with Asthenocormus, and provides a model for interpreting the less complete remains of other members of this enigmatic group of fishes.

Morphology and development of a novel murine skeletal dysplasia

BackgroundLimb bones develop and grow by endochondral ossification, which is regulated by specific cell and molecular pathways. Changes in one or more of these pathways can have severe effects on normal skeletal development, leading to skeletal dysplasias. Many skeletal dysplasias are known to result from mis-expression of major genes involved in skeletal development, but the etiology of many skeletal dysplasias remains unknown. We investigated the morphology and development of a mouse line with an uncharacterized mutation exhibiting a skeletal dysplasia-like phenotype (Nabo).MethodsWe used µCT scanning and histology to comprehensively characterize the phenotype and its development, and to determine the developmental stage when this phenotype first appears.ResultsNabo mice have shorter limb elements compared to wildtype mice, while clavicles and dermal bones of the skull are not affected. Nabo embryos at embryonic stage E14 show shorter limb cartilage condensations. The tibial growth plate in Nabo mice is wider than in wildtype, particularly in the proliferative zone, however proliferative chondrocytes show less activity than wildtype mice. Cell proliferation assays and immunohistochemistry against the chondrogenic marker Sox9 suggest relatively lower, spatially-restricted, chondrocyte proliferation activity in Nabo. Bone volume and trabecular thickness in Nabo tibiae are also decreased compared to wildtype.DiscussionOur data suggest that the Nabo mutation affects endochondral ossification only, with the strongest effects manifesting in more proximal limb structures. The phenotype appears before embryonic stage E14, suggesting that outgrowth and patterning processes may be affected. Nabo mice present a combination of skeletal dysplasia-like characteristics not present in any known skeletal dysplasia. Further genomic and molecular analysis will help to identify the genetic basis and precise developmental pathways involved in this unique skeletal dysplasia.

Mandibular dysmorphology due to abnormal embryonic osteogenesis in FGFR2-related craniosynostosis mice.

ABSTRACTOne diagnostic feature of craniosynostosis syndromes is mandibular dysgenesis. Using three mouse models of Apert, Crouzon and Pfeiffer craniosynostosis syndromes, we investigated how embryonic development of the mandible is affected by fibroblast growth factor receptor 2 (Fgfr2) mutations. Quantitative analysis of skeletal form at birth revealed differences in mandibular morphology between mice carrying Fgfr2 mutations and their littermates that do not carry the mutations. Murine embryos with the mutations associated with Apert syndrome in humans (Fgfr2+/S252W and Fgfr2+/P253R) showed an increase in the size of the osteogenic anlagen and Meckel's cartilage (MC). Changes in the microarchitecture and mineralization of the developing mandible were visualized using histological staining. The mechanism for mandibular dysgenesis in the Apert Fgfr2+/S252W mouse resulting in the most severe phenotypic effects was further analyzed in detail and found to occur to a lesser degree in the other craniosynostosis mouse models. Laser capture microdissection and RNA-seq analysis revealed transcriptomic changes in mandibular bone at embryonic day 16.5 (E16.5), highlighting increased expression of genes related to osteoclast differentiation and dysregulated genes active in bone mineralization. Increased osteoclastic activity was corroborated by TRAP assay and in situ hybridization of Csf1r and Itgb3. Upregulated expression of Enpp1 and Ank was validated in the mandible of Fgfr2+/S252W embryos, and found to result in elevated inorganic pyrophosphate concentration. Increased proliferation of osteoblasts in the mandible and chondrocytes forming MC was identified in Fgfr2+/S252W embryos at E12.5. These findings provide evidence that FGFR2 gain-of-function mutations differentially affect cartilage formation and intramembranous ossification of dermal bone, contributing to mandibular dysmorphogenesis in craniosynostosis syndromes.This article has an associated First Person interview with the joint first authors of the paper.

A coupled reaction-diffusion-strain model predicts cranial vault formation in development and disease.

How cells utilize instructions provided by genes and integrate mechanical forces generated by tissue growth to produce morphology is a fundamental question of biology. Dermal bones of the vertebrate cranial vault are formed through the direct differentiation of mesenchymal cells on the neural surface into osteoblasts through intramembranous ossification. Here we join a self-organizing Turing mechanism, computational biomechanics, and experimental data to produce a 3D representative model of the growing cerebral surface, cranial vault bones, and sutures. We show how changes in single parameters regulating signaling during osteoblast differentiation and bone formation may explain cranial vault shape variation in craniofacial disorders. A key result is that toggling a parameter in our model results in closure of a cranial vault suture, an event that occurred during evolution of the cranial vault and that occurs in craniofacial disorders. Our approach provides an initial and important step toward integrating biomechanics into the genotype phenotype map to explain the production of variation in head morphology by developmental mechanisms.

The skull osteology of the blind cave cyprinid Phreatichthys andruzzii Vinciguerra, 1924

The present article describes the morphology of the skull of Phreatichthys andruzzii Vinciguerra, 1924, blind cave fish from central Somalia. The main findings concern a general flattening of the skull and the loss of several bones (coronomeckelian, prefrontal, supratemporal, intercalar, supraopercle) belonging to the various regions of the head skeleton; but the more important modifications are shown by the orbital region, consisting in the complete disappearance of lachrymal, suborbital, sclerotics, and the substantial reduction of the other circumorbital bones. Usually the cranial lateral line canals run through the dermal bones; on the contrary in P. andruzzii the canals are nearly exclusively sheathed by thin bony muffs. These are sometimes fused to the underlying dermal bones, but in several regions they remain fully separated and independent, running through the adjoining soft tissues. The considerable degree of osteological regression shown by the skull appears to be related to the high level of a...

Intense bone fluorescence reveals hidden patterns in pumpkin toadlets

The phenomenon of fluorescence can be used by animals to change effective colouration or patterning, potentially to serve functions including intra- and interspecific signalling. Initially believed to be restricted to marine animals, fluorescent colours are now being described in an increasing number of terrestrial species. Here, we describe unique, highly fluorescent patterns in two species of pumpkin toadlets (Brachycephalus ephippium and B. pitanga). We establish that the origin of the fluorescence lies in the dermal bone of the head and back, visible through a particularly thin skin. By comparing them to those of the closely related species Ischnocnema parva, we demonstrate that pumpkin toadlets’ bones are exceptionally fluorescent. We characterize the luminescence properties of the toadlets’ bones and discuss the potential function of fluorescent patterns in natural lighting conditions.

Taphonomy and palaeohistology of ornithischian dinosaur remains from the Lower Cretaceous bonebed of La Cantalera (Teruel, Spain)

The fossiliferous site of La Cantalera-1 (Teruel, Spain) has to date provided remains of more than 30 vertebrate taxa, including dinosaurs, crocodyliforms, pterosaurs, mammals, lizards, turtles, lissamphibians and teleosteans. Located in the lower part of the Blesa Formation (lower Barremian), it is one of the richest vertebrate-bearing deposits from the Lower Cretaceous of the Iberian Peninsula. In this work, taphonomic and palaeohistological studies are carried out on the basis of ornithischian (Ornithopoda and Ankylosauria) dinosaur samples in order to assess the diagenetic processes, to characterize the histological microstructures and, if possible, to make palaeobiological inferences about the state of maturation of the individuals. A variety of techniques are used in the taphonomic study, including scanning electron microscopy (SEM), cathodoluminescence (CL), X-ray diffraction (XRD) and ultraviolet fluorescence (UVF). The bone of the dinosaur samples has been converted into francolite (fluorapatite carbonate); the trabecular cavities are filled with semi-spherical forms of goethite and two different phases of calcite. In addition, the SEM and UVF techniques suggest the activity of coccoid-form bacteria and filaments of bacterial origin (biofilms?) in the bones, which possibly favoured fossilization. The dinosaur remains were subjected to fossil-diagenetic processes in a phreatic environment after a rapid burial, without appreciable seasonality effects. On the other hand, the palaeohistological study of both skeletal and dermal bones found in La Cantalera-1 shows a community of herbivorous dinosaurs composed mostly of immature ornithopods and at least one Polacanthus-like ankylosaur, as suggested by the organizational pattern of structural collagen fibres seen in some samples. The palaeobiological inferences drawn from this study support previous interpretations of a relative abundance of immature ornithischians in La Cantalera-1.

Actinopterygians of The Permian Locality Buxières-Les-Mines (Bourbonl’archambault Basin, France) and Their Relationship to Other Early Actinopterygians

Actinopterygians from the large opencast coal mine in the vicinity of the village of Buxières-les-Mines (Bourbonl’Archambault Basin, Allier, France) are revisited and redescribed based on newly studied specimens. The understanding of the anatomy of Progyrolepis heyleri POPLIN, 1999, originally described by Poplin (1999) on the basis of the upper and lower jaws only, is greatly enhanced and is relatively complete. The anatomy of the palatoquadrate, dermal bones of the skull roof, hyoid arch, operculum, suboperculum, shoulder girdle, cheek bones and branchiostegal rays is described. In addition, new observations have been made on changes in the shape of the maxilla during ontogenesis and microstructure of the teeth. Details of Progyrolepis heyleri scales, including their microstructure and morphology of the ridge scales are provided. The collection of whole individuals, body fragments and numerous isolated bones provide confirmation of the presence of Aeduella blainvillei which is the main component of the actinopterygian fauna in Buxières-les-Mines. Additional new knowledge was obtained regarding the great variability in bones of the opercular apparatus and maxilla, presence of the supraorbital, branchiostegal ray with a conspicuous hyoid process and the direction of mutual overlapping of the suboperculum and branchiostegal ray in Aeduella blainvillei (AGASSIZ, 1833). Microsculpture on the scales is redescribed in this species. Paramblypterus cf. duvernoy is the third member of the actinopterygians in the locality Buxières-les-Mines. Fragments of Paramblypterus are very rare and the bones of the skull roof are presented here. Anatomical features of Progyrolepis heyleri, Aeduella blainvillei and Paramblypterus cf. duvernoy were studied and compared with those of other Devonian and Permo-Carboniferous actinopterygians.

New Data on Enosuchid Anthracosauromorphs (Amphibia) of the Middle–Late Permian of European Russia: Part 1. Morphology of Enosuchus breviceps Konzhukova, 1955

Cranial morphology of the type species of the genus Enosuchus, E. breviceps Konzhukova, 1955, is reexamined in detail based on the holotype and previously undescribed specimens from the type locality (Isheevo; Tatarstan, Russia; uppermost Urzhumian). E. breviceps is distinguished from known anthracosauromorphs by the intense osteogenesis of the dermal and endocranial bones, well developed surface ornamentation, the absence of the intertemporal, expanded interorbital region, and very massive quadrate.

A new genus of coccolepidid actinopterygian from the Cretaceous Iguanodon-bearing locality of Bernissart, Belgium

The Barremian–Aptian (Cretaceous) locality of Bernissart, Belgium is mainly known for the Iguanodon skeletons it yielded. Nonetheless, it also delivered a rich actinopterygian fauna. Among these fishes, is the coccolepidid Coccolepis macroptera, named by Traquair at the beginning of the 20th century. The systematic revision of several taxa of the family Coccolepididae during the last two decades, not only led to changes in the taxonomic status of these taxa, but also to a much better knowledge of these fishes in general. In the light of this achievements, C. macroptera is here revised and, as a result, it is placed in its own new genus Barbalepis. Barbalepis is a coccolepidid fish with the following combination of characters: lower jaw long and robust; pectoral fins proportionally much smaller than the pelvic fins; some dermal bones covered with a fingerprint-like thin striation and some others smooth; free area of scales covered with tubercles and overlapped area with a thin striation; fin rays smooth; anal fin inserted at the first modified haemal spine. The present paper contains a complete description of this fish with taxonomic conclusions regarding the family Coccolepididae, and a brief discussion of the paleogeographic and paleoenvironmental history of the group, which indicates that the origin of the family predates its first occurrence in the known fossil record and that coccolepidids became restricted to freshwater environments during the Jurassic.

A new species of Lasalichthys (Actinopterygii, Redfieldiiformes) from the Upper Triassic Dockum Group of Howard County, Texas, with revisions to the genera Lasalichthys and Synorichthys

ABSTRACTA new species of redfieldiiform fishes, Lasalichthys otischalkensis, sp. nov., is described based on new, three-dimensionally preserved specimens from the Upper Triassic Dockum Group of Howard County, western Texas. Lasalichthys otischalkensis is diagnosed by a combination of unique traits found in the skull, including shape of maxilla, shape of preoperculum and associated cheek bones, pattern and articulation of bones in the snout, and patterns of sensory line canals in the dermal skull bones. Specimens of this new species display novel patterns in the sensory line canals of the skull that have never been observed in any other redfieldiiform. Examination and comparison of specimens of Lasalichthys and Synorichthys from the Upper Triassic Chinle Formation and Dockum Group indicates that these taxa are only distinguishable at the species level, and Synorichthys is placed into synonymy with Lasalichthys, based on comparison of diagnostic morphological characters. Lasalichthys otischalkensis represents one of the oldest redfieldiiform taxa in North America.

Depositional setting, taphonomy and geochronology of new fossil sites in the Catskill Formation (Upper Devonian) of north-central Pennsylvania, USA, including a new early tetrapod fossil

Late Devonian terrestrial floodplain environments were important sites of plant and animal diversification and evolution. Recently discovered fossil sites in the Catskill Formation in north-central Pennsylvania yield important insights into Late Devonian terrestrial environments and ecologies. The fossil sites yield the progymnosperm plant Archaeopteris ssp., Archanodon bivalves, as well as abundant placoderms, acanthodians, and sarcopterygians including a new specimen of an early tetrapod. Most vertebrate fossils occur as abraded and disarticulated teeth, scales, and dermal bone fragments within basal lags of fluvial channel-bar complexes and articulated skull material, well-preserved scales, bones, and teeth in shallow temporary channels that meandered across vegetated floodplains. Fossil sites in these nearly flat-lying fluvial strata occur in multiple stratigraphic horizons spanning hundreds of meters of stratigraphy that represent the Sherman Creek Member and overlying Duncannon Member. The strata coarsen upsection and record progressively larger channel-bar complexes and better-developed paleosols. Applied detrital muscovite 40Ar/39Ar geochronology supplies the first quantitative age data from the sampled strata and provides information on erosion rate parameters and channel network morphology. Detrital ages indicate rapid uplift, erosion, and deposition of sediments in the Catskill fluvial system during Late Devonian time. Detrital ages also indicate temporal variation and lack of depositional linkages among Late Devonian fossil sites. Variations in the fossil assemblages between sites reflect paleoecological variations among paleo-subenvironments (channel-bars vs. floodplains) and/or taphonomic processes. Vertebrate assemblages and fluvial lithofacies documented at the recently discovered sites are broadly comparable with those in slightly younger strata at Red Hill, a well-studied site ~50 km to the west that yields a diverse vertebrate assemblage, including several taxa of early tetrapods. These heterogeneous, shallow, non-marine aquatic habitats were a crucible for experimentation in limb mobility and other specializations among sarcopterygians during Late Devonian time. Integration of paleontological, sedimentological, and geochronological data offers new insights into Late Devonian fluvial ecosystem evolution.

The nature of aspidin and the evolutionary origin of bone.

Bone is the key innovation underpinning the evolution of the vertebrate skeleton, yet its origin is mired by debate over interpretation of the most primitive bone-like tissue, aspidin. This has variously been interpreted as cellular bone, acellular bone, dentine or as an intermediate of dentine and bone. The crux of the controversy is the nature of unmineralised spaces pervading the aspidin matrix, which have alternatively been interpreted as having housed cells, cell processes, or Sharpey’s Fibres. Discriminating between these hypotheses has been hindered by the limits of traditional histological methods. Here we use Synchrotron X-ray Tomographic Microscopy (srXTM) to reveal the nature of aspidin. We show the spaces exhibit a linear morphology, incompatible with interpretations that they represent voids left by cells or cell processes. Instead, these spaces represent intrinsic collagen fibre bundles that form a scaffold, about which mineral was deposited. Aspidin is thus acellular dermal bone. We reject hypotheses that it is a type of dentine, cellular bone, or transitional tissue. Our study suggests the full repertoire of skeletal tissue types was established prior to the divergence of the earliest known skeletonising vertebrates, indicating that the corresponding cell types evolved rapidly following the divergence of cyclostomes and gnathostomes.

On the occurrence of Vinctifer ferrusquiai sp. nov. (Actinopterygii, Aspidorhynchiformes) in the Kimmeridgian (Late Jurassic) deposits near Tlaxiaco, Oaxaca, southern Mexico

Vinctifer ferrusquiai sp. nov. is described in this paper. This aspidorhynchid fish was found in Kimmeridgian marine deposits of the Sabinal Formation, exposed in the Llano Yosobé, near Tlaxiaco, Oaxaca, Mexico. The single specimen of this species shows enough diagnostic characters to be included in the order Aspidorhynchiformes, the family Aspidorhynchidae, and the genus Vinctifer. These characters include an elongate rostrum consisting of the premaxillae fused and anteriorly elongated, forming a tube-like, as well as an preopercular sensory canal located close to the posterior edge of the preopercle. Other features are the lack of premaxilla, the development of a wide posterior expansion of the maxilla, and a stout triangular preopercle. A unique combination of characters supports the erection of this new species, whose ganoine on dermal bones of the head are strongly ornamented with tubercles and ridges, and the flank scales are entirely smooth and not serrated. This Jurassic record is the first indubitable pre-Cretaceous finding of Vinctifer, the oldest into the Hispanic Corridor, and the oldest in North America.

Problems in Fish-to-Tetrapod Transition: Genetic Expeditions Into Old Specimens.

The fish-to-tetrapod transition is one of the fundamental problems in evolutionary biology. A significant amount of paleontological data has revealed the morphological trajectories of skeletons, such as those of the skull, vertebrae, and appendages in vertebrate history. Shifts in bone differentiation, from dermal to endochondral bones, are key to explaining skeletal transformations during the transition from water to land. However, the genetic underpinnings underlying the evolution of dermal and endochondral bones are largely missing. Recent genetic approaches utilizing model organisms—zebrafish, frogs, chickens, and mice—reveal the molecular mechanisms underlying vertebrate skeletal development and provide new insights for how the skeletal system has evolved. Currently, our experimental horizons to test evolutionary hypotheses are being expanded to non-model organisms with state-of-the-art techniques in molecular biology and imaging. An integration of functional genomics, developmental genetics, and high-resolution CT scanning into evolutionary inquiries allows us to reevaluate our understanding of old specimens. Here, we summarize the current perspectives in genetic programs underlying the development and evolution of the dermal skull roof, shoulder girdle, and appendages. The ratio shifts of dermal and endochondral bones, and its underlying mechanisms, during the fish-to-tetrapod transition are particularly emphasized. Recent studies have suggested the novel cell origins of dermal bones, and the interchangeability between dermal and endochondral bones, obscuring the ontogenetic distinction of these two types of bones. Assimilation of ontogenetic knowledge of dermal and endochondral bones from different structures demands revisions of the prevalent consensus in the evolutionary mechanisms of vertebrate skeletal shifts.

Manufacture and characterisation of EmDerm\u2014novel hierarchically structured bio-active scaffolds for tissue regeneration

There are significant challenges for using emulsion templating as a method of manufacturing macro-porous protein scaffolds. Issues include protein denaturation by adsorption at hydrophobic interfaces, emulsion instability, oil droplet and surfactant removal after protein gelation, and compatible cross-linking methods. We investigated an oil-in-water macro-emulsion stabilised with a surfactant blend, as a template for manufacturing protein-based nano-structured bio-intelligent scaffolds (EmDerm) with tuneable micro-scale porosity for tissue regeneration. Prototype EmDerm scaffolds were made using either collagen, through thermal gelation, fibrin, through enzymatic coagulation or collagen-fibrin composite. Pore size was controlled via surfactant-to-oil phase ratio. Scaffolds were crosslink-stabilised with EDC/NHS for varying durations. Scaffold micro-architecture and porosity were characterised with SEM, and mechanical properties by tensiometry. Hydrolytic and proteolytic degradation profiles were quantified by mass decrease over time. Human dermal fibroblasts, endothelial cells and bone marrow derived mesenchymal stem cells were used to investigate cytotoxicity and cell proliferation within each scaffold. EmDerm scaffolds showed nano-scale based hierarchical structures, with mean pore diameters ranging from 40–100 microns. The Young’s modulus range was 1.1–2.9 MPa, and ultimate tensile strength was 4–16 MPa. Degradation rate was related to cross-linking duration. Each EmDerm scaffold supported excellent cell ingress and proliferation compared to the reference materials Integra™ and Matriderm™. Emulsion templating is a novel rapid method of fabricating nano-structured fibrous protein scaffolds with micro-scale pore dimensions. These scaffolds hold promising clinical potential for regeneration of the dermis and other soft tissues, e.g., for burns or chronic wound therapies.

Evolution of the developmental plasticity and a coupling between left mechanosensory neuromasts and an adaptive foraging behavior

Many animal species exhibit laterality in sensation and behavioral responses, namely, the preference for using either the left or right side of the sensory system. For example, some fish use their left eye when observing social stimuli, whereas they use their right eye to observe novel objects. However, it is largely unknown whether such laterality in sensory-behavior coupling evolves during rapid adaptation processes. Here, in the Mexican tetra, Astyanax mexicanus, we investigate the laterality in the relationship between an evolved adaptive behavior, vibration attraction behavior (VAB), and its main sensors, mechanosensory neuromasts. A. mexicanus has a surface-dwelling form and cave-dwelling forms (cavefish), whereby a surface fish ancestor colonized the new environment of a cave, eventually evolving cave-type morphologies such as increased numbers of neuromasts at the cranium. These neuromasts are known to regulate VAB, and it is known that, in teleosts, the budding (increasing) process of neuromasts is accompanied with dermal bone formation. This bone formation is largely regulated by endothelin signaling. To assess the evolutionary relationship between bone formation, neuromast budding, and VAB, we treated 1–3 month old juvenile fish with endothelin receptor antagonists. This treatment significantly increased cranial neuromasts in both surface and cavefish, and the effect was significantly more pronounced in cavefish. Antagonist treatment also increased the size of dermal bones in cavefish, but neuromast enhancement was observed earlier than dermal bone formation, suggesting that endothelin signaling may independently regulate neuromast development and bone formation. In addition, although we did not detect a major change in VAB level under this antagonist treatment, cavefish did show a positive correlation of VAB with the number of neuromasts on their left side but not their right. This laterality in correlation was observed when VAB emerged during cavefish development, but it was not seen in surface fish under any conditions tested, suggesting this laterality emerged through an evolutionary process. Above all, cavefish showed higher developmental plasticity in neuromast number and bone formation, and they showed an asymmetric correlation between the number of left-right neuromasts and VAB.