New anatomical features of radiodont oral cones from the Fezouata Biota (Early Ordovician, Morocco)

Radiodont mouthparts (oral cones) are rare in the fossil record compared to the frontal appendages and cephalic carapaces of these iconic early Palaeozoic animals. Therefore, the study of oral cones has primarily been based on their associations with other body parts, from both taxonomic and ecological perspectives. In the Fezouata Biota (Early Ordovician, Morocco), the oral cones are extremely rare; only one fragmented piece has been figured to date, with four plates. Here, we describe two new isolated oral cones with unique morphologies. Based on comparative anatomy with other taxa from the Cambrian, we propose a method using morphometrical data to identify the family and feeding strategy of these two cones and, more broadly, all isolated ones. This approach allows us to place an unidentified oral cone into a family and identify the feeding strategy as either raptorial and benthivores, because no suspension-feeding radiodont oral cone has been found so far. In the Fezouata Biota, the two oral cones probably belong to the Hurdiidae family and they might be benthivores, which is consistent with the frontal appendages known from this locality. Elemental characterisation of both specimens suggests a possible reinforcement of the region around the central opening of the oral cones, which may increase the efficiency of food processing.