Fossil Shark Vomit Reveals Ancient Basking Shark Was Eaten by Bigger Predator

A small lump of fossilized material from Slovenia has turned out to be one of the rarest kinds of evidence in paleontology: the regurgitated remains of a meal, preserved for roughly 17 million years. Described in the Swiss Journal of Palaeontology, the specimen contains fragments of gill rakers from an extinct basking shark of the genus Keasius, mingled with the broken shells and spines of sea urchins. The find marks the first confirmed occurrence of Keasius in Slovenia and pushes the known range of these plankton-feeding sharks into the southeastern reaches of the Central Paratethys, the vast shallow sea that once covered much of Central and Eastern Europe.

The specimen was recovered from yellowish marls at Meljski Hrib, a fossil-rich hillside near Maribor in northeastern Slovenia. Calcareous nannoplankton in the surrounding matrix place the deposits in Zone NN4, corresponding to the upper Burdigalian stage of the Early Miocene. During this interval, synrift subsidence within the Pannonian Basin System produced deep marine basins across the Paratethys region, and the Meljski Hrib beds accumulated in an outer-shelf to upper-slope setting at water depths of roughly 150 to 250 meters. The locality is already famous for its Miocene invertebrates, including deep-water crustaceans and mass mortality assemblages of brittle stars, but the new bromalite adds a vertebrate dimension to the site’s ecological picture.

Bromalites are fossilized digestive products, a category that includes coprolites, regurgitalites, and cololites. Distinguishing among them relies on subtle taphonomic clues. In this case, the deciding evidence is the condition of the gill rakers themselves: their surfaces show no sign of acid etching, the pitting and corrosion that stomach acids would leave behind if the material had passed through the full digestive tract. The absence of such damage, combined with the intimate association of shark remains and echinoid debris, led the researchers to interpret the concentration as a regurgitalite, the fossil record of an animal vomiting up indigestible parts of its meal.

The shark material itself comprises at least 25 fragmentary gill rakers, the bristle-like filtering structures that modern basking sharks use to strain plankton from seawater. Six of the rakers retain their basal portions, and the longest incomplete specimen measures more than 35 millimeters. The filaments are gently curved, laterally compressed, and oval in cross section, with a median longitudinal trough and surfaces that become densely and finely striated toward the apex. Alongside the rakers, micro-computed tomography revealed small polygonal plates of calcified cartilage, known as tesserae, which correspond to the branchial basket of a basking shark and support the interpretation that the material came from a decaying carcass.

Identifying the shark to genus and species required a combination of comparative morphology and quantitative shape analysis. The team conducted a two-dimensional geometric morphometric study of gill-raker bases, comparing three well-preserved Slovenian specimens against samples of the living basking shark Cetorhinus maximus and four species of the extinct genus Keasius, including type and type-series material. Principal component and canonical variates analyses showed that the Slovenian rakers fall closest to Keasius septemtrionalis, a species known from the Late Oligocene to Early Miocene of Germany. Procrustes and Mahalanobis distance measures supported this affinity, and the stratigraphic age of the deposits aligns squarely with the known temporal range of that species. Because only three intact rakers were available and they likely came from a single individual, the authors adopted the cautious designation Keasius cf. K. septemtrionalis rather than a definitive species assignment.

The genus Keasius has a remarkable history. Ranging from the Middle Eocene to the Lower Miocene, it documents an early chapter in the evolution of filter feeding among lamniform sharks, a lineage that today includes the great white and its relatives. Four species are recognized, with fossils found across Europe, North America, Antarctica, and Asia. The diversification of Keasius during the Oligocene parallels the radiation of baleen whales, reflecting a broader restructuring of plankton-based marine ecosystems during a period of rising oceanic productivity. Cetorhinids were not, in fact, the first lamniforms to evolve suspension feeding; Cretaceous forms such as Pseudomegachasma and Aquilolamna show earlier adaptations toward planktivory, but the cetorhinid record provides a nearly continuous thread from the Middle Eocene to the present day.

What makes the Slovenian specimen scientifically valuable, however, is not just the shark identification but the company the rakers keep. Embedded within the bromalite itself, rather than in the surrounding sediment, are disarticulated fragments of irregular spatangoid echinoid tests and hundreds of complete and partial spines, representing the breakdown of several sea urchin individuals. Foraminifera, including the genus Strictocostella, round out the assemblage. Because the echinoid material was ingested along with the shark remains, it demonstrates that the predator was feeding near the seafloor. This single observation eliminates several candidate producers: crocodiles could not have accessed such depths, and pelagic mammals regurgitating at the surface would have dispersed the fragile skeletal debris before it could be buried.

The most plausible culprits, the researchers conclude, are benthopelagic sharks, particularly other lamniforms or members of the family Hexanchidae, the sixgill and sevengill sharks. These taxa are known opportunistic feeders, capable of ingesting both cetorhinid carcass material and benthic invertebrates in deep-water settings. The Miocene seas of Slovenia hosted formidable candidates: the extinct broad-toothed mackerel shark Carcharodon hastalis, whose smooth-edged teeth were adapted for grasping and slicing soft tissue, and the legendary Otodus megalodon, equipped to dismember large prey or carcasses. Hexanchid sharks, as demersal dwellers, remain equally viable, since they could have swallowed cetorhinid remains together with echinoids in the same deep-water environment.

The taphonomic scenario that emerges is one of opportunistic scavenging rather than active predation. In the Early Miocene Central Paratethys, a basking shark carcass would have represented a substantial, energy-rich resource. While buoyant, it would have attracted pelagic scavengers; once it settled on the seafloor, benthic invertebrates and demersal fishes would have taken over, with benthopelagic sharks exploiting what remained. Direct predation on basking sharks cannot be entirely excluded, but the fragile preservation of the gill rakers and the absence of acid etching favor ingestion during scavenging followed by regurgitation. Documented cases of lamniform teeth embedded in marine mammal bones elsewhere in the fossil record confirm that such opportunistic feeding behavior existed among these sharks.

Beyond its forensic appeal, the specimen offers rare indirect evidence that basking sharks patrolled the Central Paratethys during the Early Miocene and that their carcasses sustained a community of deep-water scavengers. It captures, in a single fossilized moment, a trophic interaction between a planktivorous giant and the macrophagous vertebrates that fed upon its remains, illustrating the ecological complexity of Miocene marine food webs and the quiet but essential role that scavenging played in deep-sea ecosystems long before the modern ocean took shape.

Subject of Research: A fossil regurgitalite from the Early Miocene of Slovenia containing basking shark gill rakers and echinoid remains, revealing cetorhinid paleoecology and scavenging interactions in the Central Paratethys.

Article Title: An Early Miocene regurgitalite containing basking shark remains from Slovenia: insight into cetorhinid paleoecology of the Central Paratethys

Article References: Gašparič, R., Kovalchuk, O., Mazuch, M., Košťák, M., Hitij, T., Kočová Veselská, M., Kočí, T., & Barkaszi, Z. (2026). An Early Miocene regurgitalite containing basking shark remains from Slovenia: insight into cetorhinid paleoecology of the Central Paratethys. Swiss Journal of Palaeontology, 145, 839-849. https://doi.org/10.3897/sjp.145.203557

Image Credits: AI Generated

DOI: 10.3897/sjp.145.203557

Keywords: basking shark, Keasius, regurgitalite, Central Paratethys, Early Miocene, Slovenia, paleoecology, gill rakers, lamniform sharks, scavenging, bromalite, geometric morphometrics