Two nearly complete fossil mouthparts, described for the first time from the Fezouata Shale of Morocco, are offering a rare glimpse into how some of the earliest animal ecosystems’ strangest predators processed their food. The specimens, dated to the Tremadocian stage of the Early Ordovician, are oral cones — the radial, plate-ringed mouth structures of radiodonts, an order of arthropods emblematic of the Cambrian explosion. Because oral cones are extraordinarily rare in the fossil record compared with the frontal appendages and head carapaces of these animals, the new finds from the Fezouata Biota represent only the second and third oral cone material ever reported from this celebrated Konservat-Lagerstätte, and the first nearly complete ones.
Radiodonts were among the dominant predators of early Palaeozoic seas. Forty-four species have so far been discovered in sites of exceptional preservation, ranging from Cambrian Stage 3 deposits in Poland to the Lower Ordovician Fezouata Shale of Morocco, with a possible survivor into the Lower Devonian. Yet their abundances vary dramatically between localities: a single unidentified specimen is known from the Ordovician Dol-cyn Afon Gam Formation in the United Kingdom, while thousands of specimens and more than ten species have been described from the Cambrian Burgess Shale in Canada. Of the 44 described radiodont species, only 16 preserve oral cones, which is why each new specimen carries outsized scientific weight.
The name Radiodonta itself honours the mouth: the oral cone consists of a central opening surrounded by plates arranged radially, a structure so unusual that when isolated oral cones were first found at the Burgess Shale, they were described as jellyfish for almost a century before complete radiodont specimens revealed their true identity. In the Fezouata Biota, oral cones are extremely rare — only one fragmented piece, bearing four plates, had been figured to date. The two new specimens, catalogued as MGL 108045 and YPM IP 517066, change that picture considerably.
MGL 108045, housed in the Cantonal Museum of Geology in Lausanne, is the larger of the two, measuring 35.2 millimetres along its anteroposterior axis and 31.5 millimetres across its width. It preserves 24 plates in total, arranged in a tetraradial symmetry with four large plates overlapping smaller ones around a subrectangular central opening. Each of its lateral large plates carries a massive plate node roughly five millimetres in diameter, while the anteroposterior large plates are smooth. Uniquely among known radiodont oral cones, its central opening bears extensions or embayments at the corners, preserved as four depressions that create an X-shaped outline. Its inner spines are bulbous, several of them rounded rather than pointed.
YPM IP 517066, held at the Yale Peabody Museum of Natural History, is far smaller — around 3.2 millimetres in diameter — and incomplete, but its tetraradial symmetry is still recognisable through three preserved large plates. Its estimated total plate count is 32, a configuration more commonly seen in taxa such as Cambroraster, Cordaticaris, Hurdia and Peytoia. The preserved anterior large plate carries three aligned nodes, and the lateral plate bears two. Within its central opening, possible inner spines or extra inner teeth are present but poorly preserved. The 24-plate count of MGL 108045, by contrast, is unique amongst radiodont oral cones with concentric plates.
To place these isolated mouthparts into a family and infer feeding strategy, the researchers built a database of 19 anatomical characters from 17 previously published taxa and applied a suite of statistical tools: chi-squared tests, one-way PERMANOVA with a Jaccard similarity index, hierarchical clustering, principal coordinate analysis and a K-nearest-neighbours classification. The tests showed no significant global morphological variation across all radiodont families, but a significant difference emerged between Hurdiidae and Anomalocarididae, and significant overall variation distinguished feeding strategies. Individual characters — symmetry, plate number, differentiation between small and medium plates, furrowed folds and the shape of the central opening — were significantly associated with both family and feeding strategy.
The classification results place both Fezouata oral cones within the Hurdiidae family and identify them as benthivores, meaning bottom-feeding animals, rather than active raptorial predators. This assignment is consistent with the frontal appendages already known from the locality, where only hurdiid radiodonts have been described so far. The classification accuracy was estimated at 70 percent for family and 81.82 percent for feeding strategy. Notably, no suspension-feeding radiodont oral cone has ever been found, even though more than 90 percent of the 121 frontal appendages recovered from the Fezouata Shale belong to suspension-feeding radiodonts such as the gigantic Aegirocassisinae. The researchers suggest that filter feeders might not have possessed oral cones at all, instead presenting a completely different mouth structure.
The analyses also shed light on a long-standing puzzle beyond Morocco. The isolated oral cone long attributed to Guanshancaris kunmingensis, an Amplectobeluidae from the Cambrian Guanshan Biota of China, was classified by the same methods as a benthivorous hurdiid. Because there is no direct evidence linking that oral cone to Guanshancaris — the association rests on the abundance of frontal appendages at the site — the authors argue the specimen probably belongs to an undescribed hurdiid instead, a cautionary example of how classifications based on co-occurrence of other body parts can mislead.
Synchrotron micro X-ray fluorescence mapping at the PUMA beamline of the SOLEIL synchrotron in France revealed that both cones are primarily composed of iron oxides, consistent with the preservation of most Fezouata fossils, whose metal signatures originate from late taphonomic weathering of carbonaceous or pyritised remains. Crucially, the elemental distribution is not homogeneous: in both specimens, the region around the central opening is enriched in iron and arsenic relative to the outer margin, with copper enrichment also observed in YPM IP 517066. Because trace-element incorporation into iron oxides has been shown to differ between tissue types in Fezouata fossils — with enrichment occurring in sclerotised tissues — this pattern suggests the region around the central opening was more heavily sclerotised, or reinforced, than the outer plates, plausibly to withstand the mechanical demands of feeding and to increase food-processing efficiency. The authors ruled out alternative explanations: calculations based on the attenuation properties of goethite and haematite show that differences in fossil thickness or porosity alone cannot account for the observed contrasts, and differential weathering is unlikely for a largely planar fossil lying along the bedding surface.
Comparable preservation patterns, with better survival of the plates around the central opening, appear in oral cones from the Wheeler Formation and Spence Shale of North America, and similar colour differences extend to the gnathobase-like structures of Amplectobeluidae radiodonts, hinting that reinforcement of feeding structures may have been widespread in the group. The authors caution that chemical characterisation of a broader range of oral cones, gnathobase-like structures and frontal appendages is still needed to confirm the nature and extent of this reinforcement. Even so, the two Moroccan mouthparts demonstrate that isolated oral cones, long neglected in favour of frontal appendages, can now be assigned to a family and a feeding strategy through morphometric analysis — opening a new window onto the ecology and evolution of some of the most iconic animals of the early Palaeozoic oceans.
Subject of Research: Radiodont oral cone fossils from the Early Ordovician Fezouata Biota of Morocco and their taxonomy, feeding ecology and elemental preservation
Article Title: New anatomical features of radiodont oral cones from the Fezouata Biota (Early Ordovician, Morocco)
Article References: Potin, G. J. M., Gueriau, P., Schöder, S., Saleh, F., & Daley, A. C. (2026). New anatomical features of radiodont oral cones from the Fezouata Biota (Early Ordovician, Morocco). Swiss Journal of Palaeontology, 145, 1061-1079. https://doi.org/10.3897/sjp.145.198852
Image Credits: AI Generated
Keywords: radiodonts, oral cones, Fezouata Biota, Ordovician, Morocco, Hurdiidae, paleontology, feeding strategy, synchrotron X-ray fluorescence, taphonomy, benthivores, Cambrian explosion
News Source: Drew Townsend. (October 28, 2026). Rare Fossil Mouthparts Reveal Feeding Secrets of Ordovician Sea Predators. Scienmag.
