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The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic). Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.

The teeth of gnathostomes (jawed vertebrates) show rigidly patterned, unidirectional replacement that may or may not be associated with a shedding mechanism. These mechanisms, which are critical for the maintenance of the dentition, are incongruently distributed among extant gnathostomes. Although a permanent tooth-generating dental lamina is present in all chondrichthyans, many tetrapods and some teleosts, it is absent in the non-teleost actinopterygians. Tooth-shedding by basal hard tissue resorption occurs in most osteichthyans (including tetrapods) but not in chondrichthyans. Here we report a three-dimensional virtual dissection of the dentition of a 424-million-year-old stem osteichthyan, Andreolepis hedei , using propagation phase-contrast synchrotron microtomography, with a reconstruction of its growth history. Andreolepis , close to the common ancestor of all extant osteichthyans, shed its teeth by basal resorption but probably lacked a permanent dental lamina. This is the earliest documented instance of resorptive tooth shedding and may represent the primitive osteichthyan mode of tooth replacement. The extinct Andreolepis , an early fish that is close to the common ancestor of all bony fish and land vertebrates, shed its teeth by basal resportion—the earliest example of this mode of tooth replacement. New teeth for old When a small child sheds a milk tooth, the part that is shed is the crown, and the roots are resorbed. This seems to be the primitive pattern for all bony fishes (of which we constitute a highly derived offshoot), according to Per Ahlberg and colleagues, who have been examining tooth replacement in the fossil fish Andreolepis hedei which, at 424 million years old, is close to the ancestry of all bony fish. Andreolepis shed its teeth by basal resorption, the earliest documented instance of this phenomenon, which may represent the primitive osteichthyan mode of tooth replacement.

The ontogenetic trajectory of a marginal jawbone of Lophosteus superbus (Late Silurian, 422 Million years old), the phylogenetically most basal stem osteichthyan, visualized by synchrotron microtomography, reveals a developmental relationship between teeth and dermal odontodes that is not evident from the adult morphology. The earliest odontodes are two longitudinal founder ridges formed at the ossification center. Subsequent odontodes that are added lingually to the ridges turn into conical teeth and undergo cyclic replacement, while those added labially achieve a stellate appearance. Stellate odontodes deposited directly on the bony plate are aligned with the alternate files of teeth, whereas new tooth positions are inserted into the files of sequential addition when a gap appears. Successive teeth and overgrowing odontodes show hybrid morphologies around the oral-dermal boundary, suggesting signal cross-communication. We propose that teeth and dermal odontodes are modifications of a single system, regulated and differentiated by the oral and dermal epithelia. Human teeth are an example of odontodes: hard structures made of a material called dentine that are sometimes coated in enamel. Teeth are the only odontodes humans have, but other vertebrates (animals with backbones) have tooth-like scales on their skin. These structures are called dermal odontodes, and sharks and rays, for example, are covered with them. How these structures evolved, and whether teeth or dermal odontodes developed first, continues to spark great discussion among palaeontologists. Some researchers think that teeth evolved from dermal odontodes, a theory known as the ‘scales-to-teeth’ hypothesis. Others think dermal odontodes are distinct from teeth because they lack the same spatial organization. To investigate this further, palaeontologists are looking at the earliest examples of odontodes they can find: fossils of early vertebrates that carry both teeth and dermal odontodes. Here, Chen et al. have studied Lophosteus , one of the earliest bony fishes that lived more than 400 million years ago, to explore early tooth evolution and growth patterns. Chen et al. digitally dissected a fossilized Lophosteus jawbone using submicron X-ray imaging, a technique with resolution to less than one millionth of a metre. Imaging thin sections of the specimen, found in Estonia, Chen et al. reconstructed the entire sequence of odontode development in the bony fish in 3D. The analysis showed that teeth and dermal odontodes initially take shape together but differentiate as they grow, presumably instructed to do so by various developmental signals. However, at a later stage, the two types of odontodes become similar in appearance again, suggesting that they respond to each other’s signals. For example, as the jawbone grows, dermal odontodes overgrow the earliest formed teeth. These younger odontodes resemble teeth, while the new teeth developing near the dermal odontodes take after dermal odontodes. These findings suggest that teeth and dermal odontodes are not wholly separate systems but, instead, are closely related on a molecular level. The results also show that contrary to the ‘scale-to-teeth’ hypothesis, teeth do not evolve from fully formed dermal odontodes, rather the two types of odontodes form out of one founder. This research builds on our knowledge from modern sharks and points to a previously unrecognised evolutionary relationship between teeth and dermal odontodes. It also furthers our understanding of how molecular regulation controls development.

Sharks (Selachimorpha) are iconic marine predators that have survived multiple mass extinctions over geologic time. Their prolific fossil record is represented mainly by isolated shed teeth, which provide the basis for reconstructing deep time diversity changes affecting different selachimorph clades. By contrast, corresponding shifts in shark ecology, as measured through morphological disparity, have received comparatively limited analytical attention. Here, we use a geometric morphometric approach to comprehensively examine tooth morphologies in multiple shark lineages traversing the catastrophic end-Cretaceous mass extinction—this event terminated the Mesozoic Era 66 million years ago. Our results show that selachimorphs maintained virtually static levels of dental disparity in most of their constituent clades across the Cretaceous–Paleogene interval. Nevertheless, selective extinctions did impact apex predator species characterized by triangular blade-like teeth. This is particularly evident among lamniforms, which included the dominant Cretaceous anacoracids. Conversely, other groups, such as carcharhiniforms and orectolobiforms, experienced disparity modifications, while heterodontiforms, hexanchiforms, squaliforms, squatiniforms, and †synechodontiforms were not overtly affected. Finally, while some lamniform lineages disappeared, others underwent postextinction disparity increases, especially odontaspidids, which are typified by narrow-cusped teeth adapted for feeding on fishes. Notably, this increase coincides with the early Paleogene radiation of teleosts as a possible prey source, and the geographic relocation of disparity sampling “hotspots,” perhaps indicating a regionally disjunct extinction recovery. Ultimately, our study reveals a complex morphological response to the end-Cretaceous mass extinction and highlights an event that influenced the evolution of modern sharks.

Sauropterygia is a clade of Mesozoic marine reptiles that includes the eosauropterygian Simosaurus gaillardoti Von Meyer, 1842, classically considered to be a member of Nothosauroidea. The braincase of this species has thus far only been studied in acid-prepared specimens. Acid preparation is a destructive technique prone to information loss, e.g. , through the dissolution of thin braincase bones. Here, one well-preserved skull (SMNS 16363) that remains partially embedded in matrix has been visualised using X-ray micro-computed tomography, and the braincase region has been virtually extracted. This braincase provides valuable information on the general shape of the endocast, the existence and shape of epipterygoids, which were previously considered absent in the taxon, the course of cranial nerves and the bifurcation of the internal carotid arteries along an expanded and broad parabasisphenoid, the latter extending in a tapering cultriform process to the level of the external and internal narial openings. The arrangement of the semicircular canals of the inner ear confirms previously hypothesised adaptations for near-shore aquatic life in the species. The anatomical similarities of the braincases between Simosaurus gaillardoti and Nothosaurus marchicus, including a jugular foramen that is framed by the exoccipital medially and by the opisthotic laterally, support the current phylogenetic placement of the former as an early branching member of Nothosauroidea. The cranial flattening observed in nothosaurs relative to the less dorsoventrally flattened skull of Simosaurus reflects diverging feeding strategies. Most nothosaurs were fish-trap ambush predators, whereas Simosaurus gaillardoti had durophagous, as well as (opportunistic) piscivorous capacities. These results might indicate that specialised piscivorous predation using fish-trap dentition could be independently derived in nothosaurs and in pistosauroids (including plesiosaurs).

Using 12 104 publications from 2014 to 2023 in the DeepBone database, this study employs bibliometric methods, including full-text latent Dirichlet allocation (LDA) modelling, co-occurrence network analysis and geographic mapping with ArcGIS, to examine three key aspects of vertebrate palaeontology development: geographic distribution of newly established taxa, gender demographics among researchers and research trends. Gender data were analysed using automated tools with manual verification to ensure accuracy, while methodological evolution was investigated through systematic text mining and classification. Among 8336 newly established taxa, mammals (34.72%) and fishes (29.76%) dominate, followed by reptiles (25.34%), birds (7.39%) and amphibians (2.80%). Geographic analysis reveals significant regional disparities, with the USA (13.50%) and China (13.32%) contributing the most, while Africa and Oceania remain under-represented (less than 10%). Gender analysis indicates a gradual increase in female representation from 22.78 to 27.20% over the decade, highlighting the imperative to address gender disparities in vertebrate palaeontology, thereby advancing equity in alignment with UNESCO Sustainable Development Goal 5. LDA topic modelling identifies 15 distinct research topics, encompassing evolutionary biology, cranial and skeletal morphology, dinosaur–bird evolution and human evolution, while co-occurrence analysis highlights the evolution of research methodologies, revealing strong interconnections between phylogenetic analysis (15%), traditional morphological analysis (12%) and high-resolution imaging techniques (9%).

The debate about the origin of the vertebrate dentition has been given fresh fuel by new fossil discoveries and developmental studies of extant animals. Odontodes (teeth or tooth-like structures) can be found in two distinct regions, the 'internal' oropharyngeal cavity and the 'external' skin. A recent hypothesis argues that regularly patterned odontodes is a specific oropharyngeal feature, whereas odontodes in the external skeleton lack this organization. However, this argument relies on the skeletal system of modern chondrichthyans (sharks and their relatives), which differ from other gnathostome (jawed vertebrate) groups in not having dermal bones associated with the odontodes. Their external skeleton is also composed of monoodontode 'placoid scales', whereas the scales of most early fossil gnathostomes are polyodontode, i.e. constructed from several odontodes on a shared bony base. Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRµCT) is used to study the polyodontode scales of the early bony fish Andreolepis hedei. The odontodes constructing a single scale are reconstructed in 3D, and a linear and regular growth mechanism similar to that in a gnathostome dentition is confirmed, together with a second, gap-filling growth mechanism. Acanthodian tooth whorls are described, which show that ossification of the whorl base preceded and probably patterned the development of the dental lamina, in contrast to the condition in sharks where the dental lamina develops early and patterns the dentition.The new findings reveal, for the first time, how polyodontode scales grow in 3D in an extinct bony fish. They show that dentition-like odontode patterning occurs on scales and that the primary patterning unit of a tooth whorl may be the bony base rather than the odontodes it carries. These results contradict the hypothesis that oropharyngeal and external odontode skeletons are fundamentally separate and suggest that the importance of dermal bone interactions to odontode patterning has been underestimated.

Like a fish out of water The origin of tetrapods during the Devonian period, around 350 million years ago, was a key step in vertebrate evolution. The first and arguably the single most important discovery in the study of Devonian tetrapods was Ichthyostega , the four-legged fish from Greenland first described in 1932. Now, based on the original material and more recently collected specimens, a new reconstruction of Ichthyostega has been made. It differs radically from previous versions in having a regionalized vertebral column that bears a striking resemblance to that of a mammal. The presacral vertebral column appears to have almost no lateral flexibility, but there is vertical flexibility in the lumbar region. This suggests that Ichthyostega could move on land using a bilaterally symmetrical ‘shuffling’ action. It may have been an early and ultimately unsuccessful attempt at adapting the tetrapod body plan of terrestrial locomotion, a problem solved by a tetrapod lineage quite closely related to Ichthyostega . Ichthyostega was the first Devonian tetrapod to be subject to a whole-body reconstruction 1 , 2 , 3 . It remains, together with Acanthostega 4 , one of only two Devonian tetrapods for which near-complete postcranial material is available. It is thus crucially important for our understanding of the earliest stages of tetrapod evolution and terrestrialization. Here we show a new reconstruction of Ichthyostega based on extensive re-examination of original material and augmented by recently collected specimens. Our reconstruction differs substantially from those previously published and reveals hitherto unrecognized regionalization in the vertebral column. Ichthyostega is the earliest vertebrate to show obvious adaptations for non-swimming locomotion. Uniquely among early tetrapods, the presacral vertebral column shows pronounced regionalization of neural arch morphology, suggesting that it was adapted for dorsoventral rather than lateral flexion.

Lophosteus superbus is one of only a handful of probable stem-group osteichthyans known from the fossil record. First collected and described in the late 19th century from the upper Silurian Saaremaa Cliff locality in Estonia, it is known from a wealth of disarticulated scales, fin spines, and bone fragments. In this study we provide the first description of the morphology and paleohistology of a fin spine and scale from Lophosteus using virtual thin sections and 3D reconstructions that were segmented using phase-contrast synchrotron X-ray microtomography. These data reveal that both structures have fully or partially buried odontodes, which retain fine morphological details in older generations, including sharp nodes and serrated ridgelets. The vascular architecture of the fin spine tip, which is composed of several layers of longitudinally directed bone vascular canals, is much more complex compared to the bulbous horizontal canals within the scale, but they both have distinctive networks of ascending canals within each individual odontode. Other histological characteristics that can be observed from the data are cell spaces and Sharpey’s fibers that, when combined with the vascularization, could help to provide insights into the growth of the structure. The 3D data of the scales from Lophosteus superbus is similar to comparable data from other fossil osteichthyans, and the morphology of the reconstructed buried odontodes from this species is identical to scale material of Lophosteus ohesaarensis , casting doubt on the validity of that species. The 3D data presented in this paper is the first for fossil fin spines and so comparable data is not yet available. However, the overall morphology and histology seems to be similar to the structure of placoderm dermal plates. The 3D datasets presented here provide show that microtomography is a powerful tool for investigating the three-dimensional microstructure of fossils, which is difficult to study using traditional histological methods. These results also increase the utility of fin spines and scales suggest that these data are a potentially rich source of morphological data that could be used for studying questions relating to early vertebrate growth and evolution.

In this work, previously published occurrences of vertebrates from the latest Llandovery to end-Ludlow successions of Gotland, Sweden, are gathered and summarized in an updated stratigraphic framework, which also incorporates facies differences of sedimentary units. Even though the taxonomy of vertebrates from Gotland is in need of revision, their occurrences are here reported on a group level in order to give preliminary indications of where the focus of continued sampling should lie. Indeed, there are parts of Gotland that are poorly represented by the samples at hand and others that have been extensively sampled but still have not yielded any vertebrates. Preliminary investigations of new samples indicate that the lack of vertebrates in older sediments of Gotland may be because of sampling bias, while the reasons for a complete absence of vertebrates in other parts remain unknown. Our results also emphasize a sudden appearance of acanthodians on Gotland in the early Ludfordian. To investigate these preliminary results, complementary sampling and more confined facies-categorization will be needed. Combined with a higher taxonomical resolution, this will also help us understand how the vertebrate faunas were affected by the events coupled with extinctions that have been identified on Gotland and on a global scale. One of these events has been shown to affect the Gotland vertebrates before. Our results indicate that this may be true for several of the events. When an increased understanding of the vertebrate faunas of Gotland has been established, the goal is to use up-to-date correlations to compare Gotland with other parts of the Baltic Basin to render a better picture of early vertebrate evolution during the Silurian.