Extant and ancient cephalopods—including octopuses, squids, extinct ammonites, cuttlefish, and nautiluses—have all had to solve the problem of buoyancy, whether they have hard external shells or not.

Among ancient cephalopods, internal structures such as the siphuncle, chambers, septa, and septal necks were used to regulate buoyancy. The siphuncle—a tube running through the shell chambers—is central to this system since it can be filled with water or gas to control buoyancy. It is regarded as one of the key evolutionary innovations that distinguishes cephalopods from other mollusks. Unfortunately, due to the lack of a continuous fossil record, the detailed evolution of the siphuncle has been unclear.

Now, an international research team has discovered the earliest known siphuncle-bearing cephalopod from the early Cambrian of South China, providing new insights into the group’s early origin and evolutionary history.

Dr. PAN Bing of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, in collaboration with researchers from China, the United Kingdom, and the United States under the leadership of Prof. GUO Junfeng of Chang’an University, discovered a new fossil species, Eoceras shaanxiense, which was recovered from the approximately 520-million-year-old Shuijingtuo Formation in South China.

The findings were published in Nature on July 29.

The earliest accepted cephalopod, Plectronoceras cambria, dates to the late Cambrian period about 30 million of years younger than the divergence time of cephalopods estimated by molecular clocks during the Cambrian Explosion (early Cambrian). Thus, the researchers have been trying to find more earlier fossil records of cephalopods, especially in the early Cambrian. The abundant multi-phylum microfossils known as “small shelly fossils” including diverse mollusks and their close relative groups occurred and distributed worldwide in early Cambrian rocks, and may offer great potential for discovering the earliest cephalopods.

Targeting at the small shelly fossils of the early Cambrian Shuijingtuo Formation as a potential resource, the researchers identified 32 specimens of E. shaanxiense and concluded it is an early cephalopod.

Using scanning electron microscopy (SEM) and micro-computed tomography (micro-CT), the researchers examined the specimens—which were preserved through different types of phosphatization—to reconstruct the overall external morphology and internal anatomy of the new species.

Eoceras is millimeter in size, with an orthoconic shell, an oblique apertural margin, multiple septa, and a ventrally situated segmented tube that appears to bridge the septa via minute canals. After making a comprehensive comparison of its internal structures with those of typical siphuncle-bearing cephalopods, the researchers concluded that the segmented tube of Eoceras is indeed a siphuncle—making these fossils the earliest known examples of siphuncle-bearing cephalopods. The researchers argue that Eoceras represents an intermediate evolutionary stage between earlier species with chambered shells and later species with more developed buoyancy systems.

The researchers also outlined a general early evolutionary pathway for cephalopods: First, early cephalopods originated from a taxon characterized by orthoconic shells and multiple septa. Second, cephalopods evolved a sealed, segmented siphuncle within the orthoconic shell. Third, they evolved a true siphuncle with septal necks and connecting rings.

Due to its primitive and simple buoyancy regulation system, Eoceras likely had a mostly benthic lifestyle. However, the fossil lacks features observed in later cephalopods, and its soft-body anatomy is unclear. The researchers note that additional Cambrian fossil discoveries are essential to further resolve the earliest stages of cephalopod evolution and the origin of their distinctive shell architecture.

This study was supported by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Opening Foundation of the State Key Laboratory of Continental Evolution and Early Life.

Journal

Nature

DOI

10.1038/s41586-026-10868-y

The key breakthrough in this study was the employment of an advanced imaging analysis technique that digitally reconstructs entire fossil-bearing rock samples in three dimensions. By employing this non-destructive, high-resolution scanning methodology, the research team was able to virtually "mine" fossils embedded deep within geological matrices without damaging them. This digital fossil-mining approach unlocked a veritable treasure trove of cephalopod remains, notably one thousand fossilized beaks from cephalopods preserved within Late Cretaceous sedimentary deposits in Japan, a region hitherto considered challenging for fossil recovery due to the fragility of the specimens.

Unlike many other marine organisms with hard, calcified shells that fossilize readily, squids belong to a group characterized by soft, malleable bodies prone to rapid decay after death. This intrinsic biological limitation has made direct evidence of early squids extremely scarce in the fossil record. However, squids possess chitinous beaks—rigid mouthparts essential for capturing and consuming prey—that are significantly more resistant to fossilization. Recognizing this, the researchers focused their digitization efforts on isolating these beak fossils, which serve as precious anatomical markers capable of elucidating evolutionary developments.

The extensive fossil assemblage uncovered included 263 distinct squid specimens, representing approximately 40 previously unknown species. This unprecedented diversity underscores a vastly richer and more complex cephalopod fauna in ancient oceans than previously imagined. Moreover, the comparative abundance of squid fossils relative to those of ammonites—long considered emblematic successful swimmers of the Mesozoic seas—and bony fishes reveals that squids held a conspicuously dominant ecological status during this period. This stands in stark contrast to earlier assumptions that relegated squids to a lesser role in ancient marine food webs.

The research findings presented by Dr. Shin Ikegami and colleagues paint a vivid picture of Cretaceous seascapes where squids inhabited a range of ecological niches, showcasing substantial variation in body size and abundance. Remarkably, the body sizes of these ancient squids were as large as contemporary fish and often exceeded those of coexisting ammonites, illustrating their prowess as agile and formidable predators. This discovery challenges long-held perceptions and invites a fundamental reevaluation of marine ecosystem dynamics during a pivotal chapter in Earth’s biological history.

Adding further intrigue, the study identified fossil evidence for the presence of both main modern squid clades dating back 100 million years. These clades—Myopsida, typically coastal squids, and Oegopsida, open-ocean dwellers—have until now been presumed to have diverged and flourished only following the catastrophic Cretaceous-Paleogene extinction event approximately 65 million years ago. The revelation that these lineages were already established and diversified tens of millions of years prior upends traditional timelines of cephalopod evolution and suggests that squids were pioneers of complex marine predation much earlier than previously documented.

The application of high-resolution digital tomography and imaging analysis played a pivotal role in identifying and distinguishing these fossilized beaks with exceptional clarity and precision. This methodological advancement facilitates not only the identification of species but also the reconstruction of their morphological variation and evolutionary trends, offering a powerful tool for paleobiologists. Digital fossil-mining thus emerges as a transformative approach, opening new frontiers in the study of soft-bodied organisms historically underrepresented in the fossil record due to preservation biases.

Professor Yasuhiro Iba, who spearheaded this innovative investigation, emphasizes the broader implications for our understanding of marine evolutionary biology. The newfound abundance and diversity of ancient squids imply that they were among the earliest fast, intelligent swimmers exerting significant predatory pressure in their ecosystems. By dominating marine food chains, squids may have catalyzed co-evolutionary dynamics, influencing the evolutionary trajectories of prey species and shaping the structure of ancient oceanic communities.

This research, funded in part by the Japan Society for the Promotion of Science and the Japan Aerospace Exploration Agency, exemplifies the power of interdisciplinary collaboration. It integrates paleontology, computational imaging, and evolutionary biology to tackle longstanding scientific questions regarding early marine vertebrate and invertebrate relationships. Furthermore, it underscores the necessity of advanced technological applications in uncovering the hidden depths of the fossil record and reconstructing the history of life on Earth.

The study’s findings demand a recalibration of marine paleoenvironments, highlighting squids as crucial actors shaping ecosystem dynamics millions of years before the rise of modern marine fauna. By challenging previously established extinction-related diversification models, this research shifts the paradigm—portraying squids not as latecomers but as ancient pioneers that thrive long before the demise of the dinosaurs. Such insights provide a fresh lens through which to view cephalopod evolution and the broader narrative of marine biodiversity through deep time.

In addition to its scientific ramifications, the discovery intrigues the public imagination by illuminating the hidden history of one of the ocean’s most enigmatic creatures. The ability to digitally extract and visualize these fragile fossils sets a technological benchmark, inspiring future studies that may uncover even more surprising chapters of evolutionary history, hidden within rocks around the globe. As research progresses, we can anticipate further revelations about the origins, adaptations, and ecological roles of squids in prehistoric oceans.

The study also prompts reflection on the evolutionary mechanisms underlying cephalopods’ rapid radiation and ecological dominance. Squids’ sophisticated nervous systems, advanced locomotor capabilities, and behavioral complexity are hallmarks of their success in modern oceans, traits arguably honed over tens of millions of years. By unlocking deep evolutionary roots, this research may eventually shed light on the genetic and developmental underpinnings of these remarkable biological innovations.

Altogether, the discovery not only fills a significant gap in paleontological knowledge but also elevates squids to a central position in marine evolutionary narratives. It reveals a vibrant tableau of an ancient ocean teeming with these agile and intelligent invertebrates, flourishing long before their contemporaries. The fusion of digital fossil-mining with traditional paleontological frameworks represents a paradigm shift, demonstrating how technology can redefine our understanding of life’s profound history beneath the waves.

Subject of Research: Not applicable
Article Title: Origin and radiation of squids revealed by digital fossil-mining
News Publication Date: 26-Jun-2025
Web References: http://dx.doi.org/10.1126/science.adu6248
References: Ikegami et al., Science, June 26, 2025
Image Credits: Ikegami et al., Science, June 26, 2025
Keywords: Evolutionary biology, Imaging