A Morphological Study of Radiodont Fossils from the Ordovician Fezouata Formation in the Anti-Atlas Mountains, Southeastern Morocco

The lower Ordovician Fezouata Konservat-Lagerstätte in the Anti-Atlas Mountains of southeastern Morocco provides an evolutionally window of Ordovician marine biota. Because the Fezouata Konservat-Lagerstätte includes not only Ordovician-type fauna, but also several Cambrian-type taxa, making it an important for understanding the transition of organisms between these two periods. Three genera and four species of radiodonts have been reported from this Fezouata Formation, of which two genera and three species are considered to be filter feeders. In this study, we conducted morphological and taxonomic analyses of three newly discovered filter-feeding radiodont specimens from the Zagora region of Morocco (hereafter referred to as specimens A, B, and C). Specimen A preserves part of the head carapace (H-element) and frontal appendages. The carapace is relatively small, with a length of approximately 40 cm compared with Aegirocassis benmoulai, and the frontal appendages show similarities to those of the genus Aegirocassis, suggesting that it may represent a closely related species or a juvenile individual of the genus Aegirocassis. Specimen B represents a part of the head carapace (P-element) and is considered to have been recovered together with specimen A; however, it is unclear whether it belongs to the same individual. Specimen C shows a nearly complete frontal appendage, which exhibits a distinctive spine-like structure on the dorsal side of each podomere. Although other features, such as, number of podomere of the frontal appendage, comb-like ventral spine of each podomere, have been reported in Hurdiid radiodonts (Aegirocassis, Cambroraster), combination of characters haves not been previously recorded from the radiodonts, suggesting the possibility that this specimen represents a new species.