The Toarcian stage of the Early Jurassic is famous among palaeontologists for the spectacular fossils of the Posidonienschiefer Formation in south-western Germany, where thousands of articulated ichthyosaur skeletons have been unearthed from the laminated black shales around Holzmaden. Britain, by contrast, has long seemed like a poor cousin. Although ichthyosaurs have been documented from the Whitby coastline, Strawberry Bank in Somerset and Rutland, most British Toarcian specimens are historical, fragmentary or poorly prepared, making confident identification notoriously difficult. Three genera are known from the Yorkshire area during this interval, Temnodontosaurus, Eurhinosaurus and Stenopterygius, but assessing the taxonomic position of most specimens has been a persistent headache for researchers.

Part of the problem lies in the tangled taxonomic history of Stenopterygius itself. Around the beginning of the twenty-first century, eight species were recognised as valid, diagnosed using intracranial ratios, dentition, body size, limb proportions and vertebral counts. In 2008, a major revision reduced the number to three, S. quadriscissus, S. triscissus and S. uniter, while re-assigning some material to the new genus Hauffiopteryx. In 2012, new bivariate and multivariate metrics allowed species determination across all ontogenetic stages, but the method depended on the pelvic girdle, hind-limb, articulated limbs and complete undamaged jaws, characters that are simply missing from most specimens. Small individuals lacking a hind-limb, like the Ravenscar ichthyosaur, remained impossible to refer to species with any confidence.

The new study tackled this gap by exploring postcranial metrics that work even when the skull or hind-limb is damaged or absent. The researchers measured the caudal skeletons of 40 specimens of Stenopterygius from the Posidonienschiefer Formation, assigned to species using independent criteria, and the proximal fore-limbs of 46 specimens in total. Two measurements proved especially powerful. The first is the ratio of postflexural length to total caudal length, essentially how much of the tail lies behind the tailbend. The second is the ratio of the ulnar facet to the radial facet of the intermedium, a small wrist bone whose articular surfaces for the radius and ulna differ measurably between species.

The results are strikingly clean. Stenopterygius quadriscissus has a postflexural length to total caudal length ratio of 0.39 on average, while S. triscissus averages 0.34, and the tailstock vertebral count differs as well, with a mean of 35.6 vertebrae in S. quadriscissus against 39.8 in S. triscissus. The intermedium ratio is even more decisive, with no overlap at all between S. quadriscissus, where the ulnar to radial facet ratio averages 0.84, and S. triscissus, where it averages 1.36. The third species, now called S. longipes, falls between the two with a ratio of 1.09. These metrics allowed the team to refer SMNS 55110 to S. quadriscissus, whose postflexural ratio of 0.42 and intermedium ratio of 1.01 sit squarely within the range of that species and outside the ranges of the others.

The comparative work also triggered two significant synonymies. Stenopterygius longipes, first named in 1876, had been declared a nomen dubium in 1998 on the grounds that its type skeleton, a large mounted specimen at the Palaeontological Collection of Tübingen University, might be a composite with fore-limbs that do not belong to the rest of the animal. Re-examination showed that the humeri are exposed in anterior view consistent with specimen taphonomy, that the pathological fusion and exostoses seen in the hind-limbs also appear in the fore-limbs, and that what was interpreted as a duplicated ulna is likely a fragment of the badly fractured right humerus. The team concluded the skeleton belongs to a single individual and that S. longipes is the senior synonym of S. uniter.

The second synonymy is even more dramatic. Magnipterygius huenei, erected in 2022 as a new genus of Early Jurassic ichthyosaur based on a small specimen from the Posidonienschiefer, was diagnosed by its small size, low vertebral counts and caudal proportions. The new study found that the holotype is actually an osteologically immature individual at postnatal stage 1, with a flat humeral articular surface, open sutures between fore-limb elements and a parietal bearing a dorsal triangular platform, all characters of very young Stenopterygius. Its low presacral count can be explained taphonomically, as headfirst seafloor arrival can displace cervical centra inside the skull, and counting presacral ribs instead yields 45 vertebrae, well within the range of S. quadriscissus. Its caudal proportions and intermedium ratio of 0.79 are likewise consistent only with S. quadriscissus, so Magnipterygius huenei is now considered a junior synonym of that species.

The description of SMNS 55110 itself reveals a remarkably informative skeleton. The specimen is 145.8 centimetres long, exposed on its right lateral side for most of its body length, with a complete articulated vertebral column of 134 vertebrae, 46 presacral, 80 preflexural and 54 postflexural. The skull is exposed ventro-laterally, revealing the mandible and palate in unusual detail, and at least 12 teeth are preserved near the jaws, with smooth crowns about 4 millimetres high and deep apicobasal grooves on the roots indicating plicidentine. Both fore-limbs are complete and fully articulated, showing the humerus, radius, ulna, carpals, metacarpals and phalanges in exquisite detail, though the hind-limbs and pelvic girdle are missing. Four dorsal ribs show callus formation at mid-shaft, evidence of traumatic injury sustained during the animal’s life, a common finding in juvenile Stenopterygius.

The taphonomic story behind the specimen is equally compelling. The unusually curled axial skeleton prompted the researchers to consider whether it might be a regurgitalite of a large predator, but no vertebral torsion, breakage, perimortem fractures or bite traces support that interpretation. Instead, a complex scenario emerges: the carcass arrived at the seafloor in a roughly dorsal orientation, the skull penetrated the soft sediment first and anchored the rostrum, the specimen rolled onto its left side, and current activity pushed the partially lifted postcranium while the skull stayed embedded, creating the curve in the vertebral column. The orientation of small bivalves called Meleagrinella clustered above the vertebral column, with their umbos directed down-current, supports this reconstruction, and their presence indicates deposition during a relatively short oxic to dysoxic period at the sediment-water interface.

The broader implications reshape the palaeobiogeography of Toarcian ichthyosaurs across Europe. The new metrics allowed the team to re-evaluate specimens from Luxembourg, Switzerland, France, Germany and Britain, confirming that S. quadriscissus ranged from south-western Germany to the Cleveland Basin of Yorkshire, including Luxembourg and the Wessex Basin at Strawberry Bank, while S. triscissus is confirmed only in the south-west German Basin and Switzerland and is absent from Strawberry Bank. The stratigraphic range of S. quadriscissus extends from the Tenuicostatum to Bifrons Zones, an estimated 3.3 million years. Differences in caudal morphology between the two species may even reflect differences in locomotor specialisation and habitat use, with the higher tailstock vertebral count of S. triscissus potentially indicating faster, more efficient swimming in more pelagic environments, while S. quadriscissus may have preferred nearshore habitats. The Ravenscar specimen also reinforces the presence of S. quadrisscus during the Bifrons Zone, making it one of the youngest stratigraphic occurrences of the species and demonstrating that these dolphin-like reptiles thrived in the northernmost reaches of the European epicontinental sea long after the hyperthermal Toarcian Oceanic Anoxic Event had reshaped marine ecosystems.

Subject of Research: Species delineation and palaeobiogeography of the Early Jurassic ichthyosaur genus Stenopterygius based on a new specimen from Yorkshire

Article Title: A well-preserved specimen of Stenopterygius quadriscissus ( Reptilia , Ichthyosauria ) from the Early Jurassic (Toarcian) of Yorkshire, UK and new insights into species delineation in the genus

Article References: Biot, T., Lomax, D. R., Miedema, F., & Maxwell, E. E. (2026). A well-preserved specimen of Stenopterygius quadriscissus (Reptilia, Ichthyosauria) from the Early Jurassic (Toarcian) of Yorkshire, UK and new insights into species delineation in the genus. Fossil Record, 29(1), 185-210. https://doi.org/10.3897/fr.29.185733

Image Credits: AI Generated

DOI: 10.3897/fr.29.185733

Keywords: Stenopterygius, ichthyosaur, Toarcian, Early Jurassic, Yorkshire, Whitby Mudstone Formation, SMNS 55110, taxonomy, palaeobiogeography, Magnipterygius, Posidonienschiefer, marine reptiles

The study, led by Chang Huang, Zhiyuan Ren, and Nengshui Ding of Jiangxi Agricultural University together with colleagues at Aonong Group and Jiangxi Science and Technology Normal University, focused on runs of homozygosity, or ROH. These are continuous segments of the genome in which an animal carries two identical copies of the same ancestral DNA sequence, one from each parent. When two parents share recent common ancestors, their offspring are likely to inherit matching segments on both sides, producing these long homozygous tracts. Because their length reflects how far back in the pedigree the shared ancestor lived, ROH provide a genome-wide, DNA-level measure of inbreeding that is often more accurate and more informative than traditional pedigree-based estimates, which depend on complete and accurate record keeping that commercial herds rarely have.

To capture this signal, the team analyzed genotypes from 5,859 pigs after stringent quality control, drawn from the three American breed populations. They defined ROH as segments of at least one megabase, one million DNA letters, and restricted their search to autosomes 1 through 18, excluding the sex chromosomes to keep the analysis comparable across males and females. Across all animals they detected a remarkable 416,225 individual ROH segments. That sheer number illustrates how pervasive autozygosity is in commercial breeding populations, where decades of selection for lean growth, litter size, and carcass quality have reshaped the genome through both deliberate selection and the unavoidable relatedness that accumulates in closed breeding lines.

One of the clearest findings was that the three breeds differ in their overall ROH burden. American Duroc pigs showed the highest individual-level ROH of the three populations. This pattern is consistent with the breeding structure of terminal sire lines, which are often maintained in relatively small nucleus herds under intense selection for growth and meat quality, conditions that tend to concentrate ancestral haplotypes. Landrace and Yorkshire, maternal breeds selected primarily for reproductive performance, showed different ROH architectures. The differences among breeds matter because they suggest that the historical sources of inbreeding, whether from small effective population sizes, founder effects, or selection sweeps, have acted with different intensities in each genetic line.

The heart of the study, however, lay in asking whether this autozygosity has consequences that can be measured in the barn. The researchers computed for each animal a genomic inbreeding coefficient, FROH, defined as the proportion of the autosomal genome covered by ROH. They then tested whether FROH was associated with a panel of production-related traits, using mixed statistical models that included a genomic relationship matrix. This matrix accounts for the ordinary kinship among all animals in the dataset, a crucial control, because relatives resemble each other both genetically and phenotypically for reasons that have nothing to do with inbreeding per se. Without this correction, any association between FROH and a trait could simply reflect family structure rather than the specific effect of homozygous segments.

Across 51 population-by-trait tests, the team identified 19 nominally significant associations between FROH and production traits at a probability threshold of 0.05. Thirteen of these survived correction for the false discovery rate using the Benjamini-Hochberg procedure, a statistical safeguard that limits the expected proportion of false positives among the declared findings. The pattern of surviving associations was strikingly uneven. American Landrace showed the broadest set of FDR-supported associations, Duroc had fewer, and in Yorkshire the nominal associations were restricted to body length and body height, with only the body height association holding up after correction. This breed-by-breed heterogeneity is the study’s central message: the genomic consequences of inbreeding are not a universal constant but depend on which population is being examined and which trait is being measured.

Why should different breeds show different inbreeding effects? The likely explanation lies in the concept of inbreeding load. Recessive deleterious variants are scattered across every genome, but their identity and genomic location differ among populations, shaped by each breed’s unique history of selection and drift. When autozygous segments arise, they expose whatever recessive variants happen to lie within them. If a breed’s deleterious burden happens to overlap regions influencing, say, body length or backfat, inbreeding will depress those particular traits. If the burden lies elsewhere, different traits will suffer. The population-specific associations observed here are exactly what this model predicts, and they argue strongly against a one-size-fits-all approach to managing inbreeding in multi-breed breeding programs.

The study also probed two more subtle questions. First, the researchers asked whether the effect of FROH differed between males and females, testing FROH-by-sex interactions. They found 45 estimable interaction tests, with some nominally significant results in Duroc, but none of these survived false discovery rate correction, meaning the evidence for sex-specific inbreeding effects remains tentative at best. Second, they used segmented regression models to look for thresholds, points beyond which additional autozygosity might cause a disproportionate decline in performance. Here they detected 25 nominally significant threshold responses, but again none survived FDR correction, with the smallest corrected value reaching 0.118. Importantly, the candidate breakpoints suggested by these exploratory analyses differed by population, trait, and ROH length class, hinting that if true thresholds exist, they are not universal values but properties of each population’s genome.

The distinction between ROH length classes deserves attention because it carries biological meaning. Short ROH reflect ancient shared ancestors, often reaching back many generations or even to the founding of the breed, while long ROH flag recent inbreeding, typically within the last few generations. Long ROH are therefore the ones most responsive to current mating decisions. The observation that associations and candidate thresholds varied across length classes suggests that old and new inbreeding may contribute differently to trait variation, a finding that could eventually help breeders distinguish the inbreeding they can control through mating plans from the legacy burden embedded in the breed’s history.

For the pork industry, the practical implications are concrete. Genomic inbreeding coefficients computed from routine SNP chip data could be incorporated into selection indices and mate allocation algorithms, allowing breeding companies to balance genetic gain against the accumulation of autozygosity on a population-specific basis. Rather than imposing a generic inbreeding ceiling, programs could weight the traits that are demonstrably sensitive to FROH in each line. The authors note that their findings provide a basis for population-specific evaluation of inbreeding load and for improving genomic management strategies in commercial pig breeding. As genomic selection accelerates the rate of genetic change, it also accelerates the loss of genetic diversity, making tools that measure and manage autozygosity directly from DNA increasingly essential. This study demonstrates both the promise of that approach and the statistical caution needed to interpret it: the strongest signals are real and breed-specific, while the more tantalizing patterns of sex effects and inbreeding thresholds remain, for now, hypotheses for larger datasets to test.

Subject of Research: Associations between runs of homozygosity-based genomic inbreeding and production traits in three commercial pig populations

Article Title: Runs of homozygosity reveal associations between autozygosity and production traits in three commercial pig populations

Article References: Huang, C., Ren, Z., Yang, W., Meng, Q., Wu, G., Chen, H., & Ding, N. (2026). Runs of homozygosity reveal associations between autozygosity and production traits in three commercial pig populations. BMC Genomics. https://doi.org/10.1186/s12864-026-13326-1

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13326-1

Keywords: runs of homozygosity, autozygosity, genomic inbreeding, pigs, Duroc, Landrace, Yorkshire, production traits, FROH, genomic selection, animal breeding, quantitative genetics

The study, led by researchers at the University of York together with geochemists at Curtin University in Australia, applied high-resolution isotopic fingerprinting to microscopic minerals locked inside the megaliths. The Devil’s Arrows are carved from Pennine Basin Millstone Grit, a coarse-grained sandstone deposited during the Namurian period more than 300 million years ago, while the monument itself stands on Triassic Sherwood Sandstone. Crucially, the nearest gritstone outcrops lie only about five kilometres west of Boroughbridge, and other long-suspected sources such as Plumpton Rocks sit around 13 kilometres away. If the stones had simply been glacial erratics dropped by ice, their chemistry should match one of these closer sources.

By mapping the unique mineral age profiles of zircon and apatite crystals extracted from the stones, the team traced the monoliths’ exact geological birthplace to Brimham Rocks, a dramatic gritstone landscape 18 kilometres to the west in North Yorkshire. The isotopic signatures ruled out every local and intermediate candidate, settling a debate that has run for decades over whether human effort or glaciers were responsible for positioning the giants. The answer is unambiguous: Neolithic builders knowingly bypassed convenient stone in favour of a specific, distant and presumably sacred source.

Dr Jim Leary of the University of York’s Department of Archaeology noted that megalithic architecture ranks among the most visually striking features of the Neolithic landscape across Britain and Ireland, from vast ceremonial complexes such as Avebury and Stonehenge to solitary standing stones. Yet while sites in southern England and Scotland attract considerable scholarly attention, monuments like the Devil’s Arrows have remained comparatively understudied despite their obvious significance. The new results, he said, prove that Neolithic communities moved several 25-tonne stones across Yorkshire, turning a familiar site into an epic quest to create a sacred landscape.

The scale of the monument alone justifies that description. At almost seven metres tall, the three surviving pillars form the tallest standing stone row in Britain, dwarfing the sarsens of Stonehenge. The southern stone is the second-tallest megalith in the country after the Rudston Monolith, and the central stone ranks third. The three unevenly spaced monoliths stretch across 174 metres on gently sloping ground aligned toward a possible prehistoric ford on the River Ure, and historical records indicate the row once contained at least five stones and probably more.

The study also solved a centuries-old local mystery by confirming that one of the lost Arrows is hiding in plain sight. The Tudor antiquarian John Leland recorded a fourth standing stone in the mid-16th century, but decades later it had vanished. In 1687 it was reported that locals broke up a fallen stone, using part of it to build Peg Bridge over the River Tutt and carrying the top segment to Aldborough manor. In the 19th century, antiquarian J.R. Walbran proposed that another fallen monolith had been recycled into the Battle Cross, a 5.5-metre monument created in the 15th century to commemorate the 1322 Battle of Boroughbridge. The mineral fingerprinting has now proved Walbran right: the medieval cross still standing in Aldborough is a carved segment of a long-lost Arrow.

The find also reframes the monument’s place in the wider prehistoric landscape. Extensive Neolithic remains lie west of the stones, suggesting they formed the southern gateway to a vast sacred region between the Rivers Swale and Ure. That corridor contains seven late-Neolithic henges, the densest concentration in Britain, and the Arrows appear to have anchored its southern entrance. Choosing stone from Brimham Rocks, another striking natural landmark within that ritual geography, may have been as much a symbolic act as a practical one, physically connecting two extraordinary places in a single ceremonial network.

For the National Trust, which cares for Brimham Rocks, the research draws a direct and unexpected line between two of Yorkshire’s most celebrated landscapes. Justin Scully, general manager for Fountains Abbey and Studley Royal and Brimham Rocks, observed that the stones have inspired stories and curiosity for generations, including the much-loved legend of the Devil standing on How Hill and hurling giant stone arrows toward Boroughbridge, only for them to fall short where they stand today. The science, he noted, shows the real journey behind the folklore is every bit as extraordinary.

Heritage bodies hope the findings will support the monument’s long-term protection. Jess Tipper, Historic England’s North Region Inspector of Ancient Monuments, described the Arrows as a much-loved part of Boroughbridge’s rich heritage and welcomed the scientific discoveries that deepen understanding of their history, adding that further research will help safeguard them for everyone to enjoy.

Beyond Yorkshire, the study carries broader implications for how archaeologists read megalithic monuments everywhere. Isotopic fingerprinting of zircon and apatite now offers a powerful, non-invasive route to provenance for stones that have resisted conventional geological sourcing for centuries, and it can distinguish human transport from glacial redistribution with unprecedented confidence. As the technique is applied to other stone rows, circles and monoliths, more of Neolithic Britain’s engineered sacred landscapes are likely to emerge from under assumptions of glacial convenience. The research is published in the journal Proceedings of the Royal Society A.

Subject of Research: Provenance analysis of the Neolithic Devil's Arrows standing stones in Yorkshire

Article Title: Neolithic ‘Devil’s Arrow’ stones travelled 11 miles across Yorkshire, study reveals

Article References: Neolithic ‘Devil’s Arrow’ stones travelled 11 miles across Yorkshire, study reveals. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Devil's Arrows, Neolithic, megaliths, Yorkshire, Brimham Rocks, isotopic fingerprinting, standing stones, Boroughbridge, millstone grit, glacial erratics, archaeology, Proceedings of the Royal Society A