The affected bones, catalogued as MUPA-ATZ0101-21, MUPA-ATZ0101-22, MUPA-ATZ0101-25 and MUPA-ATZ0101-23, came from a relatively complete skeleton discovered at the El Atance fossil site in Guadalajara, central Spain. The locality and individual date to the Carnian, or Late Triassic. This is the first reported pathology within Simosauridae and the first documented non-infectious vertebral pathology among Triassic sauropterygians.

The analysis focused on the four anomalous, disarticulated centra, which lay close together near the sacral region but were no longer in their original anatomical positions. Their precise positions within the vertebral series, their order relative to one another, and the identification of their anterior and posterior articular facets could not be established reliably. The authors provisionally regarded the individual as an adult or sub-adult based on its size, skeletal measurements and degree of ossification.

Researchers conducted external and internal macroscopic comparisons using the four affected centra and a non-anomalous posterior dorsal centrum, MUPA-ATZ0101-13. They measured centrum height, length and width, along with the maximum height and width of the structures, which were designated “bulks” and numbered from 1 to 11. ImageJ was used to calculate the proportion of each articular facet occupied by one or more bulks as a percentage of the facet’s total surface area. These occupation percentages referred to combined bulks on a facet rather than to each individual structure.

High-resolution CT scans were performed on three specimens at the Servicio de Técnicas no Destructivas of the Museo Nacional de Ciencias Naturales in Madrid: two anomalous centra, MUPA-ATZ0101-25 and MUPA-ATZ0101-23, and the non-anomalous comparison centrum MUPA-ATZ0101-13. The scanner operated at 160 kV, with 3,015 projections per specimen, 1,533–1,536 images per specimen and voxel sizes of 27–31 micrometres. DICOM data were processed in Avizo 7.1 to generate three-dimensional models and bone sections.

Externally, the bulks were rounded or ovoid, sharply delimited and rugose, resembling the texture of the surrounding articular surfaces. MUPA-ATZ0101-21 had two bulks on one facet and one visible bulk on the opposite facet, where the expected second structure was affected by crushing and poor preservation. MUPA-ATZ0101-22 had a symmetrical pair on one facet, while preservation did not permit confirmation of the opposite facet. MUPA-ATZ0101-25 had paired bulks on one facet, and MUPA-ATZ0101-23 carried pairs on both facets.

The combined bulk occupation was approximately 12.3% for the pair and visible bulk on the first facet of MUPA-ATZ0101-21, while the deformed bulk on its opposite facet accounted for about 3.1%. The pair on MUPA-ATZ0101-22 occupied approximately 5.4%, and that on MUPA-ATZ0101-25 occupied 9.9%. On MUPA-ATZ0101-23, the smaller pair occupied about 5.1% of its facet, whereas the more protruding pair occupied approximately 12.7%. Overall, the anomalous pattern was confined to the most posterior dorsal region and was not found in other examined centra of the holotype or in similarly positioned vertebrae from other known P. multidentatus individuals.

CT sections showed that the internal tissue of the bulks was continuous with the surrounding bone and was not clearly differentiated from it. The periosteum covering the bulks was likewise continuous with non-anomalous periosteum, without a distinct reaction. No reactive new bone formation, necrosis, lytic inner lesions, sinuses, sequestra, disproportionate overgrowth, osteophytes or clear osteoporotic or traumatic fractures were identified. One affected centrum had a locally more porous region beneath its bulk-bearing facet, whereas comparable areas in the other affected centrum did not show the same restricted pattern. Diagonal and linear microfractures occurred in both pathological and non-pathological centra, but their timing could not be determined because no associated bone reaction or malunion was present.

The authors used differential diagnosis informed by medical and veterinary pathology literature, especially work on extinct and living reptiles. The observations did not support a tumoral origin because the bulks lacked distinct pathological internal bone and disproportionate overgrowth. Infection was not supported by the absence of necrotic tissue, reactive new bone, sinuses or sequestra. Metabolic deposition disorders were inconsistent with the absence of deposits having separate internal margins and a different internal structure. A single traumatic event was also unsupported, and the restricted, symmetrical, multifocal distribution was considered incompatible with a luxation or subluxation pattern. Osteoporosis and intervertebral-disc degeneration were likewise not supported by the absence of fractures, necrosis, osteophytes, Schmorl nodes, surface pitting or evident vertebral arthritis.

The diagnosis therefore remained uncertain. Comparable paired or button-like vertebral bulks have rarely been documented in dinosaurs, but their causes have also been debated, and many occur alongside other surface lesions. Paired symmetrical bulks had not previously been reported in this form in marine reptiles. Based on the differential diagnosis and comparisons with dinosaur vertebrae, the investigators concluded that the P. multidentatus bulks most likely reflected either long-term biomechanical stress or a congenital disorder, without assigning a definitive cause.

Subject of Research: Paleopathology of vertebral centra in the Triassic sauropterygian Paludidraco multidentatus

Article Title: Pathological vertebrae in the holotype of Paludidraco multidentatus ( Sauropterygia , Simosauridae ) from the Upper Triassic of El Atance (Central Spain)

Article References: Cabezuelo-Hernández, A., de Miguel Chaves, C., Ortega, F., & Pérez-García, A. (2025). Pathological vertebrae in the holotype of Paludidraco multidentatus (Sauropterygia, Simosauridae) from the Upper Triassic of El Atance (Central Spain). Fossil Record, 28(1), 133-145. https://doi.org/10.3897/fr.28.148714

Image Credits: AI Generated

DOI: 10.3897/fr.28.148714

Keywords: paleopathology, Paludidraco multidentatus, sauropterygia, Simosauridae, vertebral pathology, Triassic reptiles, CT scanning, biomechanical stress, congenital malformation, Pathological, vertebrae, holotype

It also reveals previously undocumented features of the animal’s skull and teeth, supplementing information from the P. ausetanum holotype, previously the only known specimen of the species. The remains are distributed across slabs about 2 centimetres thick that were once processed into pedestrian paving in Girona. CT data and alignment with an adult skull of the living dugong, Dugong dugon, showed that the slabs do not correspond to a single horizontal plane through the skull.

Both are inclined by about 28.22 degrees in lateral view, while their frontal inclinations are 4.3 and 6.0 degrees. The upper slab therefore contains structures at a vertically higher level on the right and a lower level on the left, and both slabs preserve lower anterior regions and higher posterior regions. Their separation was estimated at 11.4 millimetres.

Adding that gap to about 40 millimetres of fossil-bearing stone gives a represented skull depth of approximately 50 millimetres, equivalent to roughly 50 to 77 percent of the height of a typical Eocene–Oligocene sirenian skull. Preserved material chiefly comprises parts of a single skull. It includes portions of the rostrum, premaxilla and maxilla; the frontal, vomer and basicranium; and fragments of the zygomatic arch representing the jugal and squamosal.

The upper molars M1–M3 are preserved with their crowns and roots, while additional tooth positions are represented by alveoli. The fossil also includes parts of the basisphenoid, basioccipital and spheno-occipital eminences. CT post-processing involved segmentation of individual bones and reconstruction in three dimensions, although dense sirenian bone, surrounding limestone and iron-rich mineral inclusions reduced contrast and produced interference in some scans.

One principal correction concerns the age of the individual. The earlier report had classified the animal as at least a young adult, partly on the basis of the advanced wear on M3 and its position relative to the zygomatic-orbital bridge. The new examination establishes that it was an adult because the basisphenoid and basioccipital are firmly fused and their suture is obliterated.

The M3 is fully erupted and clearly worn, but those dental observations alone do not establish the age class. The study also revises the identification of two sockets in the upper slab: the combination of the slab’s higher anatomical level and its oblique cut indicates that they most probably held the third and fourth upper permanent premolars, P3 and P4, rather than the first and second molars. At the genus level, the clearest feature is the presence of four single-rooted upper premolar alveoli and the absence of a persistent fifth deciduous premolar, DP5.

The lack of DP5 is characteristic of Prototherium and distinguishes the specimen from Eocene sirenians in which that molariform replacement tooth was retained. The researchers considered whether DP5 might instead have been resorbed and shed as the teeth moved forward, a possibility associated with some more derived dugongines. They found no supporting evidence: the area between P4 and M1 appears unsuspicious, the preserved molar roots do not indicate mesial drift, and there are no traces of the resorption seen in other specimens where deciduous teeth were lost.

The absence of DP5 therefore remains a useful diagnostic character rather than an artifact of advanced wear. Species-level attribution depends especially on the shapes of the second and third upper molars. In MAC GIR-042375, M2 is approximately rectangular because its protoloph and metaloph have similar proportions, whereas the compared Prototherium species generally have a trapezoid M2 with a wider protoloph.

The Girona M3 is oval and tapers distally, while the M3 of P. veronense, P. intermedium, P. solei and P. montserratense is trapezoid. Of the taxa examined, only P. ausetanum shares both the rectangular M2 and oval, distally tapering M3 with the Girona specimen. Other similarities are less decisive.

The zygomatic-orbital bridge of the maxilla lies approximately level with the alveolar margin in the Girona fossil, as in P. ausetanum and P. solei, but more than 15 millimetres above that margin in P. veronense and P. intermedium. The preserved basicranium offers another character that can be compared with some, though not all, potential close relatives. The spheno-occipital eminences are concave in the Girona specimen, as in P. intermedium, but convex in P. veronense and P. montserratense.

The corresponding region of the P. ausetanum holotype is incomplete and covered by sediment, so the Girona fossil supplies information not available from the species’ only previously known specimen. CT examination also failed to confirm a left hypoglossal foramen reported in the earlier description. Molar dimensions show that the Girona animal was relatively small compared with the Prototherium taxa from Italy and close in size to P. ausetanum.

Its mesiodistal M1 length is 13.5 millimetres, approximately 2 percent smaller than the left M1 of the P. ausetanum holotype, compared with differences of about 16 percent for P. veronense and 21 percent for P. intermedium. The Girona M2 measures 17.2 millimetres and M3 20.5 millimetres. M3 is about 5 percent shorter than in P. ausetanum and 11 percent shorter than in P. veronense.

By comparison, the M2 and M3 of P. solei are approximately 13 and 12 percent smaller, respectively, than those of MAC GIR-042375, whereas the teeth of P. montserratense are nearly as large. These measurements characterize the taxon’s relatively small size; they are not the evidence used to classify the individual as an adult. The study does not resolve the wider taxonomy of Prototherium.

P. montserratense and P. solei have previously been treated as distinct species, subspecies, or synonyms of other taxa, and the new comparisons do not support a final revision. P. montserratense may be distinct from P. intermedium and could instead represent a subadult form related to P. veronense, but its holotype remains embedded in sediment and requires complete preparation. P. solei differs from P. intermedium in the position of the zygomatic-orbital bridge while sharing and differing in additional mandibular characters, making its relationship uncertain.

Phylogenetic analyses have also portrayed Prototherium as paraphyletic or polyphyletic, and the study notes that the supporting dataset and cladistic analysis should be updated before stronger conclusions are drawn about relationships within the genus and among Eocene sirenians. Broader comparisons place the Girona specimen within a diverse Eocene record of stem sirenians across the Tethyan region. Known occurrences range from Tunisia and the Pyrenean Basin to France, Italy, Hungary and Romania, forming a rough southwest-to-northeast pattern in which successively younger records extend across Europe.

The Pyrenean Basin is especially productive, holding the recently described Sobrarbesiren cardieli, regarded as the oldest adequately known quadrupedal sea cow from Eurasia, as well as the Bartonian Prototherium material from Tona and Sant Vicenç de Castellet. Together with the earliest North African evidence, the distribution supports a Tethyan setting for early pan-sirenian diversification.

Subject of Research: CT and morphological analysis of an Eocene Prototherium specimen from Girona paving stones

Article Title: New findings of Prototherium ausetanum ( Mammalia , Pan-Sirenia ) from paving stones in Girona (Catalonia, Spain)?

Article References: Voss, M., Hampe, O., Mahlow, K., & Vilanova, J. C. (2023). New findings of Prototherium ausetanum (Mammalia, Pan-Sirenia) from paving stones in Girona (Catalonia, Spain)?. Fossil Record, 26(1), 135-149. https://doi.org/10.3897/fr.26.99096

Image Credits: AI Generated

DOI: 10.3897/fr.26.99096

Keywords: Prototherium ausetanum, Eocene sirenian, CT scanning, fossil skull, Girona paving stones, Catalonia paleontology, molar morphology, Tethyan biogeography, Pan-Sirenia, fossil reconstruction, findings, Prototherium

The research, led by Zumin Xian, Qinyuan Xue, Yingtian Zhao, Qiang Li, and Min Zhu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and Qujing Normal University, is published in The Science of Nature. The team did not simply describe the external appearance of the fish. Because the specimens are articulated — meaning the bones are preserved in their life positions rather than scattered — the researchers were able to apply X-ray computed tomography, scanning the fossils layer by layer and then reconstructing the complete dermal head shield and trunk shield in three dimensions on a computer. This digital dissection revealed anatomical details that would be inaccessible on a crushed or partial specimen, including internal cavities, ridges, sensory canals, and the precise geometry of the plates that armored the animal’s face and torso.

To appreciate why this matters, it helps to understand what antiarchs actually were. They represent a highly specialized lineage of early jawed vertebrates that adapted to life on or near the sea floor, forming a major component of Devonian aquatic ecosystems. Unlike most placoderms, which had mobile neck joints allowing the head shield to lift during feeding, antiarchs evolved a rigid, box-like armor and relied on their modified pectoral appendages for locomotion and maneuvering over soft substrates. During the Middle and Late Devonian, euantiarchs achieved a nearly cosmopolitan distribution, with genera such as Bothriolepis turning up on every continent, including Antarctica. Their ubiquity makes them important index fossils for correlating Devonian rocks across the globe, and their abundance in some deposits suggests they formed dense schools in shallow waters, estuaries, and floodplains.

Yangfanyu anachoresis, however, is not just another euantiarch. In addition to displaying the diagnostic characters that define the group, the new fish retains several plesiomorphic — that is, ancestral or primitive — features that its later relatives had lost. Two of these are particularly significant: the cavity for the cranio-spinal process, an internal recess on the head shield that accommodated a bony projection from the trunk shield, and the oblique ridge on the lateral wall of the trunk shield. These features are hallmarks of more primitive antiarch lineages, such as the yunnanolepids that dominated Early Devonian faunas in South China. Their presence in Yangfanyu indicates that the earliest euantiarchs had not yet fully shed the anatomical baggage of their ancestors, providing paleontologists with a rare snapshot of a lineage caught in the act of transitioning from one body plan to another.

The phylogenetic analysis, which compiled a matrix of anatomical characters and ran them through the TNT software to generate an evolutionary tree, placed Yangfanyu at the most basal position among all known euantiarchs. In other words, it is the sister taxon to every other member of the clade — the earliest branch to split off from the euantiarch family tree. This placement is not merely a matter of adding one more twig to a branching diagram. Because Yangfanyu sits at the very base of the group, it refines what paleontologists call character polarity at the origin of the clade, clarifying which anatomical features were present in the common ancestor of all euantiarchs and which were acquired later. The result indicates that the characteristic euantiarch morphology — the distinctive head shield, the specialized pectoral appendages, the particular arrangement of trunk plates — was not assembled in a single evolutionary leap but rather through the sequential acquisition of derived characters during the earliest stages of euantiarch evolution.

This kind of finding is what evolutionary biologists refer to as a transitional form, and it is precisely the sort of evidence that can settle long-running debates about how major groups originated. For decades, the relationship between the primitive antiarch lineages of the Early Devonian and the highly successful euantiarchs of the Middle and Late Devonian has been murky, with gaps in the fossil record obscuring the sequence of anatomical changes. By extending the euantiarch record back into the Pragian, the new discovery narrows that gap and suggests that the morphological transition from primitive antiarchs to euantiarchs was underway by at least 410 million years ago, only a few million years after the first antiarchs appear in Silurian rocks.

The Guangnan locality itself is proving to be a treasure trove of Early Devonian vertebrates. The Posongchong Formation, which yields the new specimens, has previously produced a diverse array of early fish, including other placoderms and jawless forms, making it one of the most important windows into the earliest diversification of jawed vertebrates anywhere in the world. The new euantiarch adds to a growing list of discoveries from Yunnan Province that are reshaping our understanding of how the major jawed vertebrate lineages emerged and spread during the Devonian, a period sometimes called the Age of Fishes because of the extraordinary variety of aquatic vertebrates that flourished then.

What makes the discovery particularly compelling for a general audience is the sheer strangeness of the animals involved. Antiarchs are among the most morphologically bizarre of all placoderms, and their pectoral appendages — often described as fin-like or wing-like structures encased in bone — have been interpreted as adaptations for propping up the body, pushing along the substrate, or even digging into soft sediment. The fact that these appendages, along with the rest of the antiarch body plan, were already well established by the Pragian suggests that the ecological role of antiarchs as benthic specialists was in place very early in their history, long before they achieved their later cosmopolitan dominance.

The implications of the new study extend beyond antiarch phylogeny. Because euantiarchs are such abundant and widespread fossils, understanding their origins has knock-on effects for Devonian biostratigraphy — the business of using fossils to date and correlate rock layers. A 10-million-year extension of the group’s record means that euantiarch remains in rocks previously thought too old for the clade may need to be reinterpreted, and it raises the possibility that other early euantiarchs are waiting to be recognized in Pragian or even older deposits in South China and elsewhere. The researchers’ use of computed tomography and three-dimensional digital visualization also highlights a broader trend in vertebrate paleontology, in which digital dissection is revealing anatomical details that traditional preparation methods could never access, allowing paleontologists to reconstruct the complete anatomy of extinct animals from fragmentary or embedded fossils.

For now, Yangfanyu anachoresis stands as the earliest and most primitive known euantiarch, a 410-million-year-old armored fish from the riverbeds and shallow seas of what is now southwestern China. Its discovery extends the fossil record of one of the Devonian’s most successful vertebrate lineages by 10 million years, clarifies the sequence of anatomical changes that produced the classic euantiarch body plan, and adds yet another piece to the puzzle of how jawed vertebrates — the group that ultimately gave rise to sharks, bony fish, and every tetrapod, including humans — diversified during the earliest Devonian. As more specimens emerge from the Posongchong Formation and other Early Devonian localities in Yunnan, paleontologists expect the picture of antiarch origins to become even sharper, potentially revealing additional transitional forms that document the step-by-step assembly of one of the most distinctive body plans in the history of vertebrates.

Subject of Research: Paleontology

Article Title: The earliest euantiarch from the Pragian (Early Devonian) of Guangnan, Yunnan Province, China

Article References: Xian, Z., Xue, Q., Zhao, Y., Li, Q., & Zhu, M. (2026). The earliest euantiarch from the Pragian (Early Devonian) of Guangnan, Yunnan Province, China. The Science of Nature, 113(6), Article 134. https://doi.org/10.1007/s00114-026-02186-0

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02186-0

Keywords: placoderms, Devonian, antiarchs, fossils, China, evolution, CT scanning, Yangfanyu, earliest, euantiarch, Pragian, Early

The specimens examined in this study are housed at the Royal Belgian Institute of Natural Sciences in Brussels and originate from the Lutetian stage of the middle Eocene. The first individual is the holotype of Eochelone brabantica, discovered in Saint-Remy-Geest in the Walloon Brabant region, while the second is a carapace of Puppigerus camperi found in Zaventem in the Flemish Brabant Province. Both fossils were recovered from the Brussels Sand Formation, a marine stratigraphic unit that has been correlated with the calcareous nannofossil NP14 biozone. This geological context places the animals in a littoral environment, where they would have been exposed to a variety of predators, parasites, and physical hazards typical of shallow marine habitats.

The analysis of the Eochelone brabantica shell revealed multiple erosive anomalies on its costal plates, two of which showed clear signs of bone remodelling. This remodelling is a critical indicator that the turtle was alive when the damage occurred, as the body’s healing response creates new bone tissue around the injury. The most prominent mark, located on the left first costal plate, is an amorphous penetrative lesion measuring approximately 4.5 centimeters in length and 2.5 centimeters in width. It features smooth margins and an asymmetric ridge-shaped bone growth on the inner surface, suggesting a significant healing process. Another distinct mark on the left second costal plate is a circular hole about 1.7 centimeters in diameter, which penetrates through the external cortex and into the cancellous bone, accompanied by a polished osseous growth on the inner side.

To further characterize these anomalies, researchers utilized computerized axial tomography (CT) scanning to generate cross-sectional images of the shell plates. The CT scans revealed the internal morphology of the lesions, showing hyperdense bone regions indicative of newly formed tissue during the healing process. In the case of the circular erosion, the images displayed a subcircular shape with a relatively flattened base. The variations in bone density observed in the scans suggest different stages of healing, with some areas showing more advanced restoration of physical and mechanical properties. This detailed imaging allowed the researchers to confirm that the bone growth was a biological response to the injury rather than a post-mortem alteration.

Based on the size, morphology, and distribution of the marks, the study attributes the erosions on the Eochelone brabantica shell to the activity of epibiotic organisms, specifically barnacles. Barnacles are known to attach to the shells of marine turtles, and their anchoring structures can penetrate the bone, causing lesions that range from shallow pits to deep holes. The smooth internal surfaces and well-defined but irregular margins of the fossil marks are consistent with the damage caused by barnacle attachment. The presence of both small pits and deep perforations suggests that the turtle hosted barnacles at various stages of development, with the larger lesions likely resulting from mature organisms that had sufficient time to grow and cause significant stress to the host.

The second specimen, Puppigerus camperi, exhibits a different set of shell alterations, including a healed fracture and abnormal erosion in the posterior region of the carapace. The healed fracture extends from the left ninth peripheral plate toward the center of the shell, resulting in the partial loss of several plates. The smooth and irregular contour of the fracture indicates that the turtle survived the initial trauma and underwent a healing process. The study suggests that this injury was likely caused by some form of physical trauma, such as a collision or a predator attack, although the absence of specific tooth marks or mechanical deformations makes it difficult to pinpoint the exact cause. The fact that the fracture did not involve the spinal column suggests that the injury was not immediately fatal, allowing the turtle to continue its life and heal the damage.

In addition to the healed fracture, the Puppigerus camperi carapace displays several superficial marks, including pits and linear grooves scattered across the surface. These marks do not penetrate the external cortical bone layer and are therefore not associated with bone remodelling, making it difficult to determine whether they were inflicted during the turtle’s lifetime or after death. The pits, measuring approximately 0.2 centimeters in diameter, are consistent with the activity of small invasive barnacles or post-mortem invertebrate activity. The linear grooves, which are about 2.5 centimeters long and 0.5 centimeters wide, have a U-shaped profile and smooth contours, characteristics often associated with organic processes during the postmortem interval, such as solution marks made by plants or microorganisms.

The study highlights the importance of distinguishing between premortem and post-mortem shell modifications in paleontological research. By using the presence of bone remodelling as a criterion, researchers can more accurately identify the types of interactions that occurred in ancient marine ecosystems. The findings from this study provide valuable insights into the health and behaviour of Eocene sea turtles, as well as the nature of their relationships with other organisms. The ability to identify specific agents, such as barnacles, responsible for shell damage enhances our understanding of the ecological dynamics that shaped these ancient environments.

Furthermore, the detailed examination of these fossils contributes to the broader field of paleopathology, which seeks to understand disease and injury in extinct organisms. The combination of macroscopic observation, CT scanning, and 3D surface scanning offers a powerful toolkit for analyzing fossil remains and uncovering the history of life on Earth. The results of this study demonstrate that even in the fossil record, subtle details can reveal significant information about the biology and ecology of ancient animals. As researchers continue to develop new techniques for analyzing fossils, the potential to reconstruct past ecosystems and understand the evolution of marine life will only continue to grow.

In conclusion, the analysis of bioerosional marks on the shells of Eochelone brabantica and Puppigerus camperi provides a compelling case study in the interactions between ancient marine organisms and their environment. The evidence of barnacle attachment and traumatic injury offers a window into the challenges faced by sea turtles in the middle Eocene, highlighting the complexity of their ecological niche. This study not only advances our knowledge of these specific taxa but also contributes to the broader understanding of bioerosion and its role in shaping the fossil record. By integrating multiple analytical methods, researchers have been able to provide a nuanced interpretation of the shell anomalies, offering a clearer picture of life in the ancient seas of Belgium.

Subject of Research: Bioerosional marks and paleopathology in middle Eocene sea turtle fossils from Belgium

Article Title: Bioerosional marks in the shells of two sea turtle taxa from the middle Eocene of Belgium

Article References: Guerrero, A., Smith, T., & Pérez-García, A. (2025). Bioerosional marks in the shells of two sea turtle taxa from the middle Eocene of Belgium. Fossil Record, 28(1), 45-56. https://doi.org/10.3897/fr.28.141743

Image Credits: AI Generated

DOI: 10.3897/fr.28.141743

Keywords: sea turtles, Eocene fossils, bioerosion, paleopathology, barnacles, marine ecology, Belgium, CT scanning, shell damage, ancient marine environments, Bioerosional, marks

The specimen, designated as IPS36361, was recovered from the Teso de la Flecha site in Salamanca, Spain. It represents an almost complete skull, although several bones from the posterior basicranium are missing. To overcome these preservation gaps, the team scanned the specimen at the Hospital Universitari Mútua de Terrassa using a standard X-ray CT system. The resulting 542 slices, with an inter-slice distance of 0.5 mm, allowed for the creation of a precise three-dimensional model. This digital reconstruction revealed the paranasal air sinuses, the dorsal region of the forebrain, the olfactory tracts, and the nasopharyngeal ducts, structures that are typically obscured by the dense bone of the skull in physical specimens.

The nasal cavity of Diplocynodon tormis displays a complex network of air passages that are characteristic of crocodylians. The nasal airway runs anteroposteriorly from the nares to the secondary choanae, divided into the nasal passage and the nasopharyngeal ducts. The olfactory region, one of the largest chambers in the skull, is bilobate and features a sagittal groove on its dorsal surface. This region is surrounded by the pterygoids, maxillae, and frontals, and it connects directly to the olfactory lobes of the brain. The nasopharyngeal ducts, which are two parallel tubes oriented posteroventrally, join in a common passage before opening into the secondary choanae, a feature that aligns with the anatomy of extant alligatoroids.

Comparative analysis of the paranasal sinus system further supports the phylogenetic position of Diplocynodon tormis as a basal alligatoroid. The sinuses are located in the snout, lateral and ventral to the nasal airway passage, and are composed of a complex of diverticula enclosed by the maxillae. The dorsal alveolar canal, which houses the maxillary branch of the trigeminal nerve, is oriented anteroposteriorly and connects with the nasal cavity via the medial subnarial anastomosis. This anatomical arrangement is similar to that found in other alligatoroids, such as Allodaposuchus and Arenysuchus, but distinct from the more derived crocodyloids. The preservation of these structures in the fossil record provides crucial evidence for the evolutionary history of the respiratory and sensory systems in crocodylians.

The study also estimated the neurosensorial capabilities of Diplocynodon tormis by analyzing the relative sizes of the olfactory bulbs and cerebral hemispheres. The olfactory ratio, a metric used to gauge olfactory acuity, was calculated for both the holotype and a paratype specimen, STUS-344. The paratype exhibited an olfactory ratio of 1.76, which falls within the expected range for alligatoroids, while the holotype had a slightly lower ratio of 1.64. These values are lower than those observed in crocodyloids, which typically range from 1.79 to 1.82, suggesting that Diplocynodon tormis possessed an acute but not as sharp olfactory sense as its more distant relatives. This finding reinforces the hypothesis that the relative size of the olfactory bulb has a strong phylogenetic signal, independent of the overall size of the animal.

Visual acuity was assessed by examining the relative volume of the optic lobe in the brain of the paratype specimen. The optic lobe accounted for 16% of the total brain volume in STUS-344, a value that is lower than that of other medium-sized crocodylians, such as Caiman crocodilus and Osteolaemus tetraspis, which have relative volumes between 19% and 22%. This suggests that Diplocynodon tormis may have had less developed visual capabilities compared to its contemporaries. The difference in optic lobe size could be attributed to variations in ecological niche or behavioral adaptations, although further studies are needed to confirm this interpretation. The absence of preserved ocular structures in the fossil record limits the precision of these estimates, but the relative volume of the optic lobe remains a reliable proxy for visual acuity in crocodylians.

Cognitive capabilities were evaluated using the Reptile Encephalization Quotient, a metric that adjusts brain volume for body mass to account for size-related differences. The REQ for the paratype of Diplocynodon tormis was calculated to be 1.12, a value that is within the general range for crocodylians but lower than that of other medium-sized specimens. This suggests that the cognitive abilities of Diplocynodon tormis were less developed than the average for its size class. The encephalization quotient in crocodylians is often correlated with ontogenetic state and body size rather than phylogenetic position, but the lower REQ of D. tormis indicates a potential difference in neural development. Additional specimens of this taxon are required to further evaluate the encephalization quotient and to determine whether this lower value is a consistent feature of the species.

The findings of this study contribute to a broader understanding of the evolutionary patterns of inner skull cavities in crocodylians. The similarity between the inner skull cavities of Diplocynodon tormis and those of other alligatoroids supports its position as a basal member of the Alligatoroidea clade. The mosaic of crocodylian plesiomorphies and alligatoroid synapomorphies observed in the brain shape of D. tormis further reinforces this phylogenetic placement. The use of CT scanning and 3D modeling has revolutionized the study of fossil neuroanatomy, allowing researchers to access and analyze structures that were previously inaccessible. As more fossil specimens are scanned and analyzed, the evolutionary history of the crocodylian sensory and cognitive systems will become increasingly clear, providing valuable insights into the adaptive strategies that have allowed this lineage to survive for millions of years.

Despite the detailed insights provided by this study, several limitations remain. The partial preservation of the holotype specimen, particularly the absence of the hindbrain and ventral brain regions, restricts the scope of the neuroanatomical analysis. The measurements of the cerebral hemispheres in the holotype may not be as precise as required due to the incomplete preservation of this region. Additionally, the lack of preserved inner ear structures in both specimens prevents any assessment of hearing capabilities in Diplocynodon tormis. Future studies incorporating more complete specimens and a wider range of fossil crocodylians will be essential to fully understand the evolutionary trajectories of the inner skull cavities and their associated sensory and cognitive functions. The data from this study, however, provides a robust foundation for these future investigations and highlights the importance of non-invasive imaging techniques in vertebrate paleontology.

Subject of Research: Neuroanatomy and sensory capabilities of the extinct alligatoroid Diplocynodon tormis

Article Title: New data on the inner skull cavities of Diplocynodon tormis ( Crocodylia , Diplocynodontinae ) from the Duero Basin (Iberian Peninsula, Spain)

Article References: Serrano-Martínez, A., Luján, À. H., García-Pérez, Á., & Fortuny, J. (2025). New data on the inner skull cavities of Diplocynodon tormis (Crocodylia, Diplocynodontinae) from the Duero Basin (Iberian Peninsula, Spain). Fossil Record, 28(1), 67-77. https://doi.org/10.3897/fr.28.133743

Image Credits: AI Generated

DOI: 10.3897/fr.28.133743

Keywords: Diplocynodon tormis, Crocodylia, Neuroanatomy, CT Scanning, Paleontology, Alligatoroidea, Olfactory Ratio, Encephalization Quotient, Iberian Peninsula, Middle Eocene, data, inner

Trachischium snakes, often called worm-eating snakes, are among the least studied members of the colubrid family. They inhabit mid- to high-elevation forests between roughly 800 and 2,500 metres across the eastern Himalayas, northeast India and the wider Indo-Burma region. Their burrowing lifestyle makes them extraordinarily difficult to detect, and even experienced herpetologists rarely encounter them. As a result, four of the ten species now assigned to the genus have been described only within the last seven years, almost entirely as a consequence of surveys pushing into previously unexplored terrain.

The path to the new species began when researchers noticed that the Murlen specimen resembled members of Trachischium but did not match either of the two species previously recorded from Mizoram, T. hmuifang and T. reticulata. A search through the herpetology collection of the California Academy of Sciences in San Francisco revealed a second, matching specimen: an adult male collected on 13 July 2003 at Chunchuone village in Haka Township, Chin State, Myanmar, at an elevation of 1,953 metres. The two localities lie approximately 90 kilometres apart in a straight line, yet they share strikingly similar habitats, forest types and elevational bands.

Morphology alone set the new snake apart. It possesses 13 dorsal scale rows throughout the body, a feature that distinguishes it from T. monticola and T. apteii, which carry 15 rows. It has two postocular scales, whereas T. fuscum, T. guentheri, T. reticulata and T. laeve each have one. It bears two prefrontal scales, in contrast to the single prefrontal of T. fuscum, T. guentheri and T. nyalamense. Its temporal formula of one anterior and two posterior temporals differs from the single anterior temporal of T. monticola and T. apteii, and its 28 to 29 paired subcaudal scales fall outside the ranges of its closest relatives. Even its colouration is diagnostic: in preservative, the underside is brown with sparse white speckles, unlike the bright orange-red venter of T. hmuifang or the black underside of T. reticulata.

The holotype, an adult male deposited at Mizoram University in Aizawl under catalogue number MZMU 3757, measures 409 millimetres in total length, with a snout-to-vent length of 351 millimetres and a tail comprising 14 percent of its total length. The paratype, CAS 233200, is larger at 506 millimetres total length. Both animals display smooth, iridescent dorsal scales arranged in 13 rows at the neck, mid-body and anterior to the vent, with 135 ventral scales and a tapering apical spine at the tail tip. In life, the dorsum carries a lustrous blue iridescence that becomes even more vivid than in the preserved specimens.

To probe the species’ evolutionary relationships, the team extracted genomic DNA from the holotype’s preserved liver tissue and amplified fragments of the mitochondrial 16S rRNA gene and the nuclear oocyte maturation factor mos (c-mos) gene. These new sequences were combined with downloaded data for cytochrome b and the nuclear recombination activating gene 1 (RAG-1), producing a dataset of 98 sequences covering 32 species, with three outgroup taxa. Maximum likelihood analysis performed with IQ-Tree, using 100,000 ultrafast bootstrap replicates, recovered a phylogeny in which the genus formerly known as Blythia is nested firmly within Trachischium, supporting the recent proposal to treat Blythia as a junior synonym.

The phylogeny revealed three major clades within Trachischium. Clade 1 contains species from north of the Brahmaputra River, while Clade 2, the T. reticulata group to which the new species belongs, represents lineages south of the river. Clade 3 comprises species from Arunachal Pradesh and Medog County in China. Clades 2 and 3 are sister lineages with strong support, at 96 percent ML clade support, while the placement of the Murlen sample near T. reticulata received weaker support of 69 percent, hinting at further complexity within the group. The new species shows 2 to 5 percent uncorrected p-distance divergence from its congeners at the 16S gene, a level consistent with species-level distinctness.

Perhaps the most technically striking element of the description is the use of computed tomography. The paratype’s skull, scanned and made available through MorphoSource, was volume-rendered and measured in MeshLab, revealing a complete colubrid skull of 13.39 millimetres from the tip of the premaxilla to the supraoccipital. The maxilla carries 20 to 21 functional teeth of subequal size, lacking the diastema and enlarged posterior teeth typical of most other natricine genera, a derived condition shared only with T. fuscum among its relatives. The pterygoid bones display asymmetry, with 14 functional teeth on the left and 15 on the right, and the dentary bears 13 teeth. The hemipenis of the holotype, everted and examined in detail, is short and stubby with a Hemipenis Proportion Index of 0.68, weakly bilobed and densely ornamented with subequal conical spines.

The new species was named in honour of Professor Hmar Tlawmte Lalremsanga of Mizoram University, recognizing his decades of contribution to herpetology in Northeast India and his mentorship of generations of students working across the Indo-Burma biodiversity hotspot. The holotype was found actively moving along a muddy road at 21:30 h on the outskirts of Murlen National Park, at 1,560 metres elevation, shortly after a brief rainfall. When handled, the snake remained calm and showed no defensive or aggressive behaviour. Murlen National Park, covering roughly 100 square kilometres between 800 and 1,919 metres, receives 2,500 to 3,000 millimetres of annual rainfall and harbours Khasi Sub-Tropical Wet Hill Forests and Assam Sub-Tropical Pine Forests, with a rich flora of oaks, rhododendrons, bamboos and orchids.

Based on matching habitat, elevation and forest type, the authors suggest the species may also occur in northeast Mizoram, adjoining Manipur and the similar elevational realms of the Chin Hills. Historical records complicate the picture: specimens reported from the Chin Hills over a century ago bear a single postocular scale, unlike the new species, and Burmese populations described in older literature may represent T. reticulata or yet another unnamed species. The Brahmaputra River appears to act as a significant biogeographic barrier for these fossorial high-elevation snakes, with clades reciprocally monophyletic on either side, even though the river does not seem to restrict low-elevation species such as certain pitvipers. With genetic divergence among unvouchered samples suggesting that within-genus diversity remains underrepresented, and with the Indo-Burma hotspot yielding new snake species steadily over the past decade, researchers argue that increased research effort and funding for the region is urgently needed before its hidden diversity disappears unnoticed.

Subject of Research: Taxonomic description of a new fossorial snake species from the Indo-Burma biodiversity hotspot

Article Title: A new species of fossorial snake of the genus Trachischium Günther, 1858, from the Indo–Burma biodiversity hotspot

Article References: Bhardwaj, V. K., Bal, A. K., Tluanga, C. L., & Mirza, Z. A. (2026). A new species of fossorial snake of the genus Trachischium Günther, 1858, from the Indo–Burma biodiversity hotspot. Herpetozoa, 39, 203-215. https://doi.org/10.3897/herpetozoa.39.e187919

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.39.e187919

Keywords: Trachischium, new species, fossorial snake, Indo-Burma biodiversity hotspot, Mizoram, Myanmar, herpetology, natricine, phylogenetics, CT scanning, taxonomy, Murlen National Park

The two specimens, catalogued as SC000900 and SC000908, are isolated right maxillary teeth collected from the lower member of the Yuliangzi Formation at Longgushan, Jiayin County. SC000900 is an almost complete tooth crown with the basalmost portion of its root preserved, suggesting it may represent a shed tooth. SC000908, previously designated DMJY V-815, is a broken crown lacking its apex. Both are remarkably small — SC000900 has a crown height of just 9 millimeters — and both were scanned at Yinghua NDT in Shanghai using Phoenix V|tome|x systems. The scans produced voxel sizes of roughly 3.5 and 3.3 micrometers, fine enough to resolve individual dental tissues and microstructures that optical microscopy had never revealed.

Troodontids are a clade of small, bird-like theropod dinosaurs whose teeth are instantly recognizable to specialists: proportionally large denticles with an apically hooked morphology, and a distinct constriction between the crown and the root. Despite more than 170 years of documentation of troodontid fossils, stretching back to Leidy’s 1856 descriptions, the internal anatomy of their teeth has remained largely unexplored. The new CT data change that. For the first time, researchers have segmented the enamel, dentin, and pulp cavity of troodontid teeth in three dimensions, revealing a suite of previously unrecognized features that could reshape how paleontologists interpret this clade.

The pulp cavity is the star of the show. In both specimens it exhibits a blade-like shape, compressed in the labiolingual dimension, tapering sharply toward the apex, and curving distally. Its apex sits significantly lower than that of the crown. Most strikingly, the basal half of the distal margin of the pulp cavity displays nine distinct finger-like projections, spaced at approximately 0.5 millimeters, each extending toward the corresponding interdenticular diaphysis. The mesial margin is markedly convex, while the distal margin is concave. The consistency of these projections between the two teeth suggests they are genuine anatomical characters of this Yuliangzi troodontid population rather than intraspecific variation — potentially informative traits that had been hidden inside the teeth all along.

The enamel tells an equally unexpected story. In SC000900, enamel thickness measures 31, 29, and 17 micrometers at the apical, middle, and basal regions of the crown respectively, thinning progressively toward the base. The ratio of enamel thickness at the crown base to crown height is just 0.19 percent — comparable to the early bird Jeholornis prima and far lower than most other sampled early birds, such as Sapeornis chaoyangensis at 1.3 percent or Longipteryx chaoyangensis at 4.0 percent. This confirms that enamel reduction is a hallmark of troodontids. But the real surprise lies in the denticles: in both specimens, the enamel on the labial side of each mesial and distal denticle is systematically thicker than on the lingual side. This labiolingual enamel asymmetry, localized to the denticles rather than the entire crown, has never been documented in any theropod subgroup before.

Asymmetrical enamel has long been known in sauropod and ornithischian dinosaurs, where it affects the entire crown. Finding it in theropods — but confined to the denticle margins — raises intriguing functional questions. The researchers suggest this localized thickening may represent a biomechanical adaptation associated with stress distribution during feeding, or enhanced resistance to wear along the denticle margins. Testing these hypotheses will require three-dimensional finite element analysis, but the consistency of the pattern across both specimens indicates it is a real structural feature of these teeth, not a scanning artifact or a quirk of preservation.

External anatomy reinforces the troodontid identity of the teeth. SC000900 shows labiolingual compression, distal recurvature, and denticulation along both carinae — features that confidently assign it to Theropoda. The pronounced crown-root constriction and exceptionally large, hook-like denticles place it within Troodontidae. Among troodontids, the presence of large apically hooked denticles with a density of 2.2 per millimeter distally distinguishes it from genera like Byronosaurus, Mei, and Urbacodon, which lack denticles entirely. Its morphology is particularly comparable to the maxillary teeth of Troodon itself, given the denticles along the entire length of both carinae and a similar crown base length. Because the specimen is represented solely by a tooth, the authors conservatively classify it as a Troodon-morphotype tooth rather than assigning it to a named species.

That classification carries real biogeographic weight. The Troodon dental morphotype is prevalent in the Late Cretaceous of North America, and Troodon-like teeth have been recovered from Maastrichtian deposits at Kakanaut in Chukotka, in the Russian Far East. The identification of a relatively complete Troodon-morphotype tooth from the Yuliangzi Formation adds further evidence for faunal exchange between East Asia and western North America via the Cretaceous Beringia land bridge. Comparable assemblages showing strong Asian–North American affinities have been documented from the Udurchikan Formation along the Heilongjiang (Amur) River, the Kakanaut Formation, and the Hell Creek Formation of western North America — a network of records that underscores how connected these terminal Cretaceous ecosystems really were.

Within China, Maastrichtian dinosaur assemblages are distributed across Heilongjiang, Jiangxi, and Guangdong provinces, from the Yuliangzi Formation in the north to the Nanxiong Group and the Dalangshan Formation in the south. Notably, tyrannosaurids are present in all of these formations, suggesting faunal exchange among them, while differences in composition — oviraptorids and sauropods in the Ganzhou Basin, therizinosaurids and nodosaurids in the Nanxiong Basin, only tyrannosaurids in the Dalangshan Formation — may reflect paleoenvironmental factors, sampling biases, or both. In the Yuliangzi Formation itself, the only theropods definitively identified to date are tyrannosaurids and troodontids; earlier reports of dromaeosaurids, carcharodontosaurids, and other taxa may be exaggerated, as some researchers have argued that all of those teeth could be attributable to tyrannosaurids based on similar measurements.

The wear facet on SC000900 adds a final layer of detail. Situated on the lingual surface, it is elliptical in shape with smooth margins, measuring 4.3 millimeters along its longest axis and 1.0 millimeter along its shortest. Fine parallel scratches on the polished surface — slightly offset from the longest axis, positioned more apically on the mesial side and more basally on the distal side — strongly suggest a genuine wear facet rather than a fossilization artifact. Together with the internal structures revealed by CT scanning, these features establish a baseline dataset for future comparative analyses within Troodontidae. The researchers also note that the reported diversity of theropods from the Yuliangzi Formation might be exaggerated owing to the absence of comprehensive studies, and that the presence of these troodontid teeth implies the formation may yet yield theropod body fossils in addition to isolated teeth — a tantalizing prospect for future paleontological discoveries in this already storied corner of China.

Subject of Research: Paleontology

Article Title: The anatomy of two troodontid teeth from the Upper Cretaceous of Jiayin, Heilongjiang Province, China

Article References: Yin, Y.-L., Wu, B.-Y., Pei, R., Zhang, H.-G., Zhang, X., Shen, F.-B., & Xing, X. (2026). The anatomy of two troodontid teeth from the Upper Cretaceous of Jiayin, Heilongjiang Province, China. Swiss Journal of Palaeontology, 145, 823-837. https://doi.org/10.3897/sjp.145.195625

Image Credits: AI Generated

DOI: 10.3897/sjp.145.195625

Keywords: troodontids, paleontology, CT scanning, Cretaceous, Beringia, theropod teeth, Jiayin, Yuliangzi Formation, enamel, dinosaur biogeography, anatomy, troodontid

Oviraptorosaurs are among the most intriguing of all non-avian theropod dinosaurs. Fossils from this group, known chiefly from the Cretaceous of Asia and North America, display a startling array of bird-like features: pennaceous feathers, a pygostyle-like tail structure, and even evidence of brooding behavior atop their nests. These similarities make oviraptorosaurs pivotal to understanding the dinosaur-bird transition. Yet the earliest chapters of their evolutionary story are known almost exclusively from the celebrated Jehol Biota of western Liaoning, where seven species across six genera of early-diverging oviraptorosaurs have been unearthed. Four of these, Caudipteryx zoui, Caudipteryx dongi, Similicaudipteryx yixianensis and Xingtianosaurus ganqi, belong to the family Caudipteridae.

The problem has always been preservation. Most Jehol oviraptorosaur fossils are flattened in slabs, a mode of burial that obscures or distorts precisely the features paleontologists most want to study, such as the three-dimensional arrangement of the metatarsals in the foot. Compounding this gap, bone histology research on oviraptorosaurs has focused overwhelmingly on their more derived relatives, the caenagnathids and oviraptorids, leaving early-diverging taxa nearly unexamined. Before this study, histological data for Jehol oviraptorosaurs came only from limited descriptions of a Caudipteryx zoui femur and a Similicaudipteryx fibula. The new specimen directly addresses both shortcomings at once.

To reveal what the compressed fossil concealed, the team scanned PMOL-AD00126 with a GE Phoenix v|tome|x micro-CT scanner at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, operating at 180 kV and 130 microamperes and achieving a resolution of roughly 58.5 micrometers per pixel. Individual bones were then segmented slice by slice in commercial software and rendered as three-dimensional models, with data deposited openly in ScienceDB. The terminal phalanges of digits two through four were missing, but their impressions survived in the matrix, and epoxy-resin casts prepared by earlier preparators allowed the team to reconstruct the phalangeal formula as 2-3-4-5, the standard count for the group.

The three-dimensional reconstruction exposed a suite of features never before documented in a caudipterid. Most striking is the metatarsus itself: metatarsal III is strongly pinched along its shaft, yet its proximal end remains fully exposed on the front of the foot, producing what paleontologists call a subarctometatarsalian condition. This is the first unambiguous evidence of such an arrangement anywhere in Oviraptorosauria. The arctometatarsus, in which the central metatarsal is tightly clamped between its neighbors, is interpreted as a mechanically reinforced structure adapted for fast, terrestrial running, so the discovery hints that some early oviraptorosaurs were evolving toward enhanced cursorial ability, while later members of the group took locomotor evolution in more complex directions.

Other novelties abound. Metatarsal I carries pronounced dorsal and plantar prominences on its mid-shaft, structures comparable to those seen in the caenagnathids Chirostenotes and Anzu but absent in dromaeosaurids and troodontids. Metatarsals II and III bear distinct longitudinal ridges on their plantar surfaces, a feature previously recorded only in caenagnathids among coelurosaurs with an arctometatarsus. Metatarsal III also shows an elongated depression running from its dorsal mid-shaft toward the distal end, likely the insertion site of the muscle that extends the third digit, and every preserved distal phalanx displays well-developed extensor ligament pits. Together these characters paint a far richer picture of the caudipterid foot than flattened slabs ever allowed.

Taxonomically, no single feature stamps the specimen as a caudipterid, but the overall combination fits the family closely. The length ratio of metatarsal I to metatarsal II is 0.19, near Similicaudipteryx at 0.17 and well below derived oviraptorids such as Khaan at 0.26 and Ganzhousaurus at 0.29. The ratio of phalanx III-1 to metatarsal III length falls at 0.25, squarely within the caudipterid range of 0.21 to 0.30, and the proximal end of metatarsal I attaches near the distal third of metatarsal II, echoing Similicaudipteryx. The metatarsals and distal tarsals are unfused, ruling out affinities with Avimimus, Yuanyanglong and some caenagnathids, in which these elements fuse in adults. The authors therefore refer the specimen provisionally to Caudipteridae while stopping short of naming a new species.

The histological half of the study is equally revealing. Because metatarsal II alone retains an intact diaphyseal wall through its mid-distal portion, the researchers sectioned it transversely, embedding the sample in resin and grinding it to optical quality for examination under normal and polarized light. The cortex reaches a maximum thickness of about 1.6 millimeters dorsally and is lined by a thin layer of endosteal bone, indicating that expansion of the medullary cavity was largely complete. The vascular canals run predominantly lengthwise along the bone, secondary osteons are scarce, and the matrix组织 more closely resembles crossed parallel-fibered bone than either fibrolamellar or typical parallel-fibered tissue.

Crucially, the section records two single lines of arrested growth, annual pauses in bone deposition, with a double line between them. Spacing between these lines narrows toward the outer surface and vascular density declines, both signs of slowing growth. Yet the outermost cortex lacks an external fundamental system, the dense bony signal of full skeletal maturity, and retains abundant vascularity. The individual, in other words, was still growing when it died. This matters because the foot, at 216.4 millimeters in total length, exceeds that of most known caudipterid specimens yet falls far short of Similicaudipteryx, and the authors explicitly caution against assigning the specimen to any named species on size alone while the maturity of comparative fossils remains unknown.

The implications reach well beyond one fossil. Many diagnostic traits of Jehol oviraptorosaur species rest on skeletal proportions that may shift with growth, so pairing fine-grained anatomy with osteohistology offers a way to test whether named species truly differ or simply represent different life stages. The subarctometatarsalian foot, meanwhile, slots into a broader evolutionary spectrum stretching from the plesiomorphic metatarsus of Protarchaeopteryx and most oviraptorids to the fully arctometatarsalian condition of Avimimus and most caenagnathids, suggesting that running adaptations evolved repeatedly and unevenly across the group. As open CT data and thin sections circulate, this single 120-million-year-old foot promises to keep informing studies of gait, digit extension, foot stabilization and postural control in some of the most bird-like dinosaurs that ever walked the Earth.

Subject of Research: Pedal anatomy and bone histology of an early Cretaceous caudipterid oviraptorosaur from the Jehol Biota

Article Title: A near-complete caudipterid pes from the Early Cretaceous Jehol Biota reveals insights into pedal anatomy and osteohistology of early oviraptorosaurs

Article References: Han, M., Duan, M., Song, J., Hao, M., Liu, Y., Shao, S., Kubo, K., Li, Y., Wu, Q., Rummy, P., & Wang, S. (2026). A near-complete caudipterid pes from the Early Cretaceous Jehol Biota reveals insights into pedal anatomy and osteohistology of early oviraptorosaurs. Swiss Journal of Palaeontology, 145, 943-956. https://doi.org/10.3897/sjp.145.207461

Image Credits: AI Generated

DOI: 10.3897/sjp.145.207461

Keywords: oviraptorosaur, Caudipteridae, Jehol Biota, Early Cretaceous, paleontology, osteohistology, arctometatarsus, metatarsal, Liaoning, dinosaur evolution, CT scanning, growth lines

The fossil belongs to Choerosaurus dejageri, an enigmatic therocephalian therapsid that lived roughly 259 million years ago during the late Permian period. Therocephalians are close relatives of cynodonts, the group that gave rise to mammals, and baurioid therocephalians in particular evolved strikingly mammal-like features. Yet while their Triassic descendants have been studied extensively, the Permian members of the clade remain poorly known, and Choerosaurus has not received a detailed anatomical description since it was first briefly characterized in 1929.

A team led by Alessandro Gigliotti of Humboldt-Universität zu Berlin and the Museum für Naturkunde Berlin, working with colleagues from Princeton University, the North Carolina Museum of Natural Sciences, and the University of the Witwatersrand, has now changed that. The researchers CT-scanned the holotype specimen, SAM-PK-8797, housed at the Iziko South African Museum in Cape Town, using a Phoenix VTomeX L240 system with an isotropic voxel size of just 0.050 millimeters. That resolution allowed them to digitally segment and reconstruct bones that had previously been obscured by matrix or crushed beyond recognition, including the previously obscure palatal region at the roof of the mouth.

Choerosaurus is a strange animal even by therocephalian standards. Uniquely among its kind, it sports exaggerated hemispheric bosses on its cranium and lower jaw, structures that earlier CT-assisted work suggested were used in display behavior or low-energy combat, possibly covered by a cornified sheath and deployed in intimidation or ritualized sexual behavior. The new reconstruction confirms these bosses consist of two distinct types of spongy bone, a cancellous hollowed core and a denser outer layer traversed by radially oriented canals, and that their surfaces are perforated by numerous foramina likely associated with branches of the infraorbital nerve, supporting a tactile role in display.

But the real headline concerns the palate. The secondary palate, the bony shelf that separates the nasal passage from the oral cavity, is a hallmark of mammals, allowing simultaneous mastication and respiration. Within synapsids, the broader group that includes mammals and their extinct relatives, a closed secondary palate evolved independently multiple times: once in anomodonts, several times in therocephalians, and again early in cynodont history. The new study shows that Choerosaurus captures a crucial transitional stage in the therocephalian version of this story.

In Choerosaurus, the vomer, a midline bone of the snout, plays the role of an important bracing element in the palate. It forms a long sutural connection with the medially projecting shelves of the maxilla, a structure the researchers call the maxillo-vomerine bridge, which extends from the level of the upper canine to around the level of the third upper postcanine. This differs markedly from the early cynodont condition, where the palate is built instead from the medial projections of the maxillae and palatines, with the vomer excluded from the external palatal surface. The contrast highlights that therocephalian and cynodont secondary palates have different evolutionary origins despite their similar function.

The team also found that the palatal morphology of Choerosaurus closely resembles that of Lycideops longiceps, another lycideopid baurioid, supporting the hypothesis of a close relationship between the two taxa. Lycideopidae currently includes just four species, and the family is of particular importance because it exemplifies the evolutionary trajectory of non-cynodont therapsids across the Permo-Triassic boundary, showing a trend toward smaller body sizes and more delicate skulls, an instance of the so-called Lilliput Effect following the end-Permian mass extinction.

The functional significance of the palate may explain why it kept evolving independently. The researchers argue that similar selective pressures likely underpinned its origin in different lineages: strengthening the snout, providing an enhanced surface for food processing, and maintaining respiratory function during food intake. In predatory forms, trends toward palatal closure may have been tied to increasing bite force or prey handling techniques like lateral head shaking. In herbivorous forms, such as the bauriid therocephalians that were the only successful Triassic radiation of the group, a more resistant palatal surface may have helped process high-fiber forage. Notably, in cynodonts the secondary palate is also considered a prerequisite for innovations such as higher metabolic rates, endothermy, and suckling behavior, but this level of physiological integration did not occur in therocephalians or anomodonts, which went extinct during the Triassic.

The description of the Choerosaurus palate is a contribution to understanding the initial evolutionary history of synapsid secondary palate development, building on recent comprehensive sampling of the earliest cynodonts. The authors note that future CT-assisted descriptive research targeting other early baurioids and non-dicynodont anomodonts, along with more functional and paleoecological studies, will be needed to understand the selective pressures underlying these changes. For now, a single crushed skull from the Karoo has shown that the road to the mammalian palate was paved more than once, and by different bones each time.

Subject of Research: Paleontology

Article Title: Cranial anatomy of the baurioid therocephalian Choerosaurus dejageri with comments on secondary palate convergence in therocephalians and cynodonts

Article References: Gigliotti, A., Pusch, L. C., Kammerer, C. F., Benoit, J., & Fröbisch, J. (2026). Cranial anatomy of the baurioid therocephalian Choerosaurus dejageri with comments on secondary palate convergence in therocephalians and cynodonts. Frontiers in Mammal Science, 5, Article 1869886. https://doi.org/10.3389/fmamm.2026.1869886

Image Credits: AI Generated

DOI: 10.3389/fmamm.2026.1869886

Keywords: therocephalian, Choerosaurus dejageri, secondary palate, convergent evolution, CT scanning, Permian, therapsids, Lycideopidae, paleontology, Karoo, Cranial, anatomy

Megaraptorans were agile, two-legged carnivores closely related to tyrannosaurs, the lineage that includes the famous Tyrannosaurus rex. Despite that kinship, they evolved a strikingly different hunting apparatus. Rather than relying on massive jaws, megaraptorans possessed slender skulls and attacked their prey with powerfully muscled arms tipped by enormous curved claws. Some members of the group eventually grew to gigantic proportions and rose to the top of the food chain in the southern continents, but the newly described British species is among the smallest and earliest known, dating to the Early Cretaceous period roughly 120 million years ago. Its discovery in the United Kingdom places the early evolution of the group squarely on European soil.

Based on comparisons with its closest relatives, the research team estimates that Invictibellatrix amberina would have measured three to four metres in length and stood just over a metre and a half tall, roughly the height of an adult human. Lead author Dr Cassius Morrison of UCL Earth Sciences has suggested the animal likely bore feathers and that its claws may have reached lengths of around 10 to 20 centimetres. Its diet would have consisted of small dinosaurs, lizards and mammals, placing it in an ecological role comparable to that of a modern hyena: an active, capable predator and scavenger of mid-sized prey rather than the dominant carnivore of its landscape.

That ecological position is part of what makes the animal so intriguing from a human perspective. As Dr Morrison noted, although Invictibellatrix was not the apex predator of its time, a person encountering one would have faced a far more immediate danger than a T. rex. A human would represent roughly a third of the dinosaur’s body weight, making people perfectly sized prey that such an animal would very likely have pursued, whereas the much larger T. rex would have had little interest in prey so small relative to its own bulk. The comparison underscores how predator-prey dynamics in the Cretaceous differed sharply from the popular image shaped by the largest tyrannosaurs.

The identification of the new species depended on modern imaging applied to old material. The researchers subjected the fossil to computed tomography scanning, producing a three-dimensional model of the rear portion of the skull as well as a reconstruction of its internal cavity, effectively revealing the shape of the brain. Such braincase anatomy is highly informative in theropod dinosaurs, because the bones enclosing the brain carry features that vary consistently between major lineages and can therefore be used to test where a fragmentary specimen belongs on the dinosaur family tree.

The comparisons extended across a broad comparative sample of skulls and braincases from tyrannosaurs, spinosaurs, raptors and other bipedal carnivorous dinosaurs. A distinctive combination of anatomical traits emerged, including an oval opening where the spinal cord entered the brain and an hour-glass-shaped crest on the bones of the braincase. Neither feature alone would settle the question, but together they distinguished the specimen from every known species. When computer algorithms were used to analyse how the traits of the skull fit with those of other species, the results consistently placed the specimen within the megaraptoran family, confirming both its identity and its status as something previously unknown to science.

The geographic significance of the find is considerable. Megaraptorans are thought to have originated in Asia before migrating through Europe and eventually becoming apex predators across Gondwana, the southern supercontinent that comprised present-day Africa, South America and Antarctica. Until now, that hypothesis lacked a crucial piece of supporting evidence, because no megaraptoran fossils had ever been recovered from Europe. Co-author Charlie Scherer, a PhD student at UCL Earth Sciences, described the new species as the first proof that megaraptorans were present in Europe and that they reached Gondwana by that route rather than by island-hopping along more southern pathways. In effect, the Isle of Wight specimen anchors the middle leg of a dispersal story that had previously been inferred only from its endpoints.

To explore that story in more detail, the team used mathematical modelling to reconstruct how the global distribution of megaraptorans may have shifted through time. The models drew on the fossils discovered so far, the evolutionary relationships among the species, and reconstructions of ancient geography and climate. The results indicate that megaraptorans were globally widespread during the Early Cretaceous, the very interval in which Invictibellatrix lived. By the Late Cretaceous, tens of millions of years later, they had likely disappeared from Laurasia, the giant northern landmass that included modern-day Europe, while in the south they flourished as apex predators throughout Gondwana, attaining enormous sizes with claws reaching up to 35 centimetres in length.

The study did not determine why megaraptorans apparently died out in the north, but the authors point to plausible explanations that include shifts in climate or environment, or competition from other predators such as the tyrannosaurs that came to dominate northern landmasses in the Late Cretaceous. The southern record illustrates just how successful the lineage became where it survived. Maip macrothorax, recovered from rocks in what is now Argentina, is estimated to have been nine to ten metres long and to have weighed as much as an elephant, a stark contrast to the tiger-sized British pioneer described in this study.

The fossil itself carries a human history as rich as its scientific one. It was originally found at the foot of a cliff on the south-west coast of the Isle of Wight by the amateur palaeontologist Reginald Walter Tooley, and it was one of more than 1,000 specimens he discovered that were acquired by the Natural History Museum after his death. Senior author Professor Paul Barrett of the Natural History Museum emphasised that, despite more than 200 years of collecting on the island, new dinosaur species continue to emerge, and that carnivorous dinosaurs in particular have been elusive finds. Work of this kind, he noted, demonstrates the exceptional value of historical museum collections, in which many discoveries still await. The choice of name carries meaning as well: Invictibellatrix, meaning unconquered female warrior, was intended by the researchers to give hope and strength to those who are bullied, discriminated, victimised and oppressed, while amberina refers both to the amber found in the rocks where the fossil was discovered and to a female name. The research was funded by the Palaeontographical Society, the Royal Society and UKRI.

Subject of Research: Identification of a new Early Cretaceous megaraptoran theropod dinosaur species from an Isle of Wight fossil

Article Title: UK dinosaur fossil identified as new long-clawed predator

Article References: UK dinosaur fossil identified as new long-clawed predator. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Invictibellatrix amberina, megaraptoran, Isle of Wight, Early Cretaceous, theropod dinosaur, Natural History Museum, paleontology, Gondwana, Laurasia, tyrannosaurs, CT scanning, Royal Society Open Science