The original identification of Pohlsepia mazonensis as an octopus was based on external morphology and surface characteristics observable in the fossilized remains. These included apparent arm-like structures and body shapes reminiscent of octopuses, leading scientists in 2000 to postulate that this specimen represented a major pushback in the timeline of octopus evolution by roughly 150 million years. However, this interpretation always faced scrutiny, primarily because the fossil did not exhibit the complete defining features of true octopuses, such as the absence of external shells.

Recent advances in synchrotron imaging, which involves the use of extremely bright and focused beams of X-rays, permitted researchers to peer within the fossil matrix in unprecedented detail. This non-destructive technique allowed the team to detect minute internal structures hidden beneath the fossil’s surface. The new analyses revealed the presence of radular teeth, a specialized molluscan feeding apparatus comprised of rows of small teeth arranged in a ribbon-like configuration. This radical anatomical insight undermined the previous octopus attribution.

Crucially, the tooth count and morphology in the radula differed significantly from what is observed in octopuses. Octopuses typically exhibit radulae with seven to nine teeth per row, whereas the newly discovered fossil bore at least eleven teeth per row. Such characteristics are consistent with nautiloids—a group that includes the modern Nautilus—known for having up to thirteen teeth per radular row. This pattern closely matched that of another fossil species, Paleocadmus pohli, previously discovered in the same Mazon Creek deposits in Illinois.

The fossilization process had long obscured the true identity of Pohlsepia mazonensis, with post-mortem decay contributing to its octopus-like appearance. Detailed forensic examination using synchrotron light effectively conducted a “cold case” investigation of this ancient specimen, revealing that decomposition prior to fossilization altered the external morphology. These findings definitively place Pohlsepia within the nautiloid lineage, highlighting the challenges of interpreting soft-bodied fossil preservation.

This reassignment substantially impacts our understanding of cephalopod evolution and biogeographic timelines. As nautiloids are considered “living fossils” due to their conserved morphology over hundreds of millions of years, the discovery of the oldest known soft tissue of a nautiloid challenges assumptions about when soft-bodied cephalopods diversified. Pohlsepia now represents the earliest known example of soft tissue preservation in nautiloids—surpassing previous records by approximately 220 million years.

With Pohlsepia’s reevaluation, the timeline for the emergence of octopuses, scientifically known as octobrachians, shifts forward dramatically. The data now support the hypothesis that modern octopuses did not appear until the Jurassic Period, some 150 million years later than Pohlsepia’s age. Furthermore, the divergence between octopuses and their ten-armed cephalopod relatives, such as squids, likely occurred during the Mesozoic Era, overturning the idea of a Palaeozoic origin for these groups.

This discovery underscores the importance of integrating novel imaging technologies in paleontological research, particularly when evaluating enigmatic and controversial fossils. By uncovering tiny but critical anatomical features, researchers can challenge and refine long-held scientific narratives. The Pohlsepia case exemplifies how modern scientific tools can redefine evolutionary milestones and reshape textbook depictions of life’s history.

Dr. Thomas Clements, the study’s lead author and a lecturer specializing in invertebrate zoology at the University of Reading, articulated the revolutionary nature of this finding. He emphasized that this was more than just a taxonomic correction; the tiny radular teeth, preserved for 300 million years, allowed scientists to peel back the layers of history and understand cephalopod evolution with newfound clarity. Such breakthroughs demonstrate that fossil reinterpretations, driven by modern methodologies, can yield transformative insights.

The research was published on April 8, 2026, in the journal Proceedings of the Royal Society B Biological Sciences. The article, titled “Synchrotron data reveal nautiloid-characters in Pohlsepia mazonensis, refuting a Palaeozoic origin for octobrachians,” presents detailed synchrotron imaging analyses combined with comparative anatomical studies. These data collectively affirm the fossil’s placement within the Nautiloidea rather than the Octobrachia clade.

Pohlsepia’s discovery site, Mazon Creek in Illinois, is known for its exceptional fossil preservation, where soft tissues are often fossilized alongside hard parts. This makes it a crucial window into Cambrian and later faunas, shedding light on the ecology and morphology of soft-bodied and lightly sclerotized organisms. The identification of nautiloid features in this specimen enhances the paleontological significance of the Mazon Creek Lagerstätte and encourages renewed examination of existing collections under modern imaging technologies.

In summary, redefining Pohlsepia mazonensis as a nautiloid relative realigns evolutionary timelines and alters interpretations of early cephalopod diversity. It dispels the myth of the “oldest octopus” and highlights the nuanced processes by which fossils can be misinterpreted due to taphonomic effects. This milestone discovery not only reconfigures scientific understanding but also demonstrates the power of advanced imaging techniques in unlocking Earth’s deepest biological mysteries.

Subject of Research: Reassessment of Pohlsepia mazonensis fossil identity using synchrotron imaging, implications for cephalopod evolution

Article Title: Synchrotron data reveal nautiloid-characters in Pohlsepia mazonensis, refuting a Palaeozoic origin for octobrachians

News Publication Date: 8 April 2026

Image Credits: Dr Thomas Clements, University of Reading

Keywords: Pohlsepia mazonensis, cephalopod evolution, nautiloid, octopus, fossil misidentification, synchrotron imaging, radula, soft tissue preservation, Mazon Creek, Jurassic cephalopods, Paleocadmus, taphonomy

Coelacanths have long captured scientific fascination, particularly since their unexpected rediscovery in the 20th century, defying the previous belief that they were extinct. With modern representatives limited to two species within the genus Latimeria, these fish occupy a unique evolutionary niche, being more closely related to terrestrial vertebrates than to most other fish. These extant coelacanths inhabit deep marine environments, relying exclusively on gill respiration. Yet, their ancient Triassic ancestors exhibited remarkable morphological diversity, inhabiting various ecosystems and, crucially, possessing well-developed lungs encased in distinctive bony plates arranged akin to roof tiles. Until now, these lungs were primarily interpreted as air-breathing organs, but the new study ventures beyond this notion, hinting at a dual sensory and respiratory role.

Pioneering this exploration, Lionel Cavin, curator at MHNG and adjunct professor at UNIGE’s Department of Genetics and Evolution, spearheaded the examination of Triassic coelacanth fossils unearthed in Lorraine, France. Employing the European Synchrotron Radiation Facility (ESRF) in Grenoble, Cavin’s team harnessed the facility’s particle accelerator capabilities to visualize the fossils’ internal anatomy with unprecedented clarity. This non-destructive imaging unveiled remarkably preserved ossified lungs, adorned with wing-like bony extensions at their tips—structures evocative of auditory apparatus.

Supplementing fossil analysis, comparative embryological studies on modern coelacanths revealed the presence of a canal connecting the inner ear’s hearing and balance organs within the skull, a feature critical for sound transduction. Synthesizing these observations, researchers propose that in these Triassic coelacanths, the ossified lung’s bony wings operated as sound collectors, channeling vibrations through the connecting canal directly to the inner ear, effectively serving as an underwater auditory system. This hypothesis draws inspiration from known vertebrate analogs, notably the Weberian apparatus in freshwater fish like carp and catfish, where swim bladders communicate with inner ears via specialized ossicles to detect sound waves.

The Weberian apparatus exemplifies an evolutionary testament to auditory specialization, wherein an air-filled organ amplifies mechanical pressure waves, enabling fish to perceive acoustic signals underwater effectively. Translating this principle to coelacanths, the ossified lung’s structural modifications represent a parallel solution, wherein the lung, filled with air or gas, functioned as a resonating body to intercept sound vibrations otherwise imperceptible due to the aquatic environment’s density. Thus, the coelacanth’s unique lung anatomy signifies an elegant sensory adaptation enhancing environmental perception.

Intriguingly, the auditory function of the lung appears to have been lost during coelacanth evolution, correlating with their shift to deeper marine habitats. As evolutionary pressures mounted, the lungs regressed, rendering this sound detection system obsolete for modern species inhabiting oxygen-depleted abyssal zones. Nonetheless, vestigial anatomical remnants in extant coelacanth skulls retain echoes of this ancient sensory complexity, offering a portal into the evolutionary narrative of vertebrate sensory systems.

This research illuminates the multifaceted roles organs may assume across evolutionary timescales, challenging traditional, singular-function interpretations. The lung’s dual respiratory and auditory capacity in ancient coelacanths underscores the dynamic interplay of structure and function in vertebrate adaptation. Furthermore, these insights enrich our comprehension of vertebrate ancestral sensory modalities, drawing fascinating parallels with human evolutionary history and suggesting that early aquatic ancestors may have possessed similarly intricate sensory apparatuses.

The applications of advanced synchrotron imaging techniques, as demonstrated here, represent a new frontier in paleobiology, allowing scientists to decode fossilized anatomy with remarkable precision without destructive sampling. This heralds a transformative era for evolutionary biology, enabling the reconstruction of sensory systems and behaviors of extinct species with unparalleled detail.

Ultimately, the findings compel a reconsideration of how prehistoric aquatic vertebrates interacted with their environments, blending respiratory and sensory functionalities in innovative ways. By uncovering an auditory mechanism lost to deep-ocean dwelling descendants, the study enriches the mosaic of evolutionary adaptations and highlights the nuanced complexities underlying vertebrate acoustic perception.

This discovery not only unravels the hidden capabilities of coelacanth lungs but also redefines expectations of organ multifunctionality in extinct species. It invites further investigation into other fossil groups, potentially revealing additional examples where sensory and physiological systems converged uniquely in evolutionary history.

As research progresses, deciphering the evolutionary pathways that led to the coelacanth’s sensory adaptations may shed light on the early diversification of vertebrate hearing mechanisms. This could have broader implications for understanding the evolution of terrestrial hearing in vertebrates, considering coelacanths’ pivotal phylogenetic position adjacent to land-adapted species.

In sum, the revelation of a dual respiratory and auditory function in the coelacanth lung exemplifies the interplay of evolutionary innovation and environmental adaptation. This discovery, with its profound implications for sensory biology and vertebrate evolution, captures the imagination of scientists and enthusiasts alike, promising to fuel ongoing scientific inquiry and reshaping our understanding of life’s ancient underwater realms.

Subject of Research: Not applicable

Article Title: A dual respiratory and auditory function for the coelacanth lung

News Publication Date: 19-Mar-2026

Web References: http://dx.doi.org/10.1038/s42003-026-09708-6

Image Credits: © L. Manuelli–MHNG

Keywords: coelacanth, auditory system, ossified lung, synchrotron imaging, vertebrate evolution, prehistoric fish, Triassic period, inner ear, sensory biology, Weberian apparatus, underwater hearing, evolutionary biology