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| Falciscaris mumakiana Potin, Claisse, Trébaol, Gueriau, Wu, Pates & Daley, 2025 Artwork by Alexis Trébaol |
The Fezouata Shale Formation is an Early Ordovician Lagerstätte that preserved exceptionally detailed records of complex marine ecosystems, making it crucial for understanding the early evolution of animal life. It has yielded the youngest known community of radiodonts to date. This group is particularly well known from the Cambrian, with iconic representatives such as Anomalocaris, which are emblematic of the Cambrian explosion. Here we describe a new radiodont from the Fezouata Biota, Falciscaris mumakiana gen. et sp. nov. based on seven specimens of isolated frontal appendages. These appendages bear long endites with large and robust auxiliary spines, suggesting they were adapted for foraging through sediment in search of prey. The appendages of F. mumakiana gen. et sp. nov. can be relatively large compared to the majority of radiodont appendages, with endites reaching up to 11.4 cm in length, suggesting a total body size exceeding one meter for this Ordovician radiodont. In contrast, smaller specimens can be up to 10 times smaller, indicating ontogenetic stages during which the frontal appendage morphology changes little. Following the “Ordovician Plankton Revolution”, the proliferation of planktonic resources and enhanced pelagic-benthic coupling during this period likely allowed for the rise of giant suspension-feeding radiodonts, such as the Aegirocassisinae and F. mumakiana gen. et sp. nov., the new giant benthivore. In term of taxonomic diversity, benthivores radiodonts remain a minor component of radiodont diversity in the Fezouata Biota compared to the more dominant suspension feeders.
Key words: Panarthropoda, Radiodonta, Hurdiidae, gigantism, benthivores, feeding evolution, Fezouata Shale, Early Ordovician.
Superphylum Panarthropoda Nielsen, 1995
Order Radiodonta Collins, 1996
Family Hurdiidae Lerosey-Aubril & Pates, 2018
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| Hurdiid radiodont Falciscaris mumakiana gen. et sp. nov. frontal appendage, from the Fezouata Shale Formation, Lower Ordovician, Morocco. YPM IP 516782a/b, holotype and paratypes |
Genus Falciscaris nov.
Etymology: From Latin falx (genitive falcis), scythe, in recognition of the strongly curved shape of the endites tips; and Latinised Greek caris, crab, commonly used in arthropod taxonomy.
Falciscaris mumakiana sp. nov.
Etymology: Mûmak (plural mûmakil) is a fantasy elephant-like animal from the Tolkien universe Lord of the Rings. They are described as giant animals and are depicted in the third part of the movie trilogy as having 4 long curved tusks equipped with spines, looking like the curved and spiny endite of Falciscaris mumakiana gen. et sp. nov.
Diagnosis.—Hurdiidae frontal appendage with at least seven podomeres: one proximal, five intermediate and one distal. Proximal podomeres rectangular, taller than long. At least six laminiform endites are present, long ones on five intermediate podomeres and a shorter one distally. Intermediate endites over twice the height of podomeres, all ending in a strongly curved, hook-like tip. Each endite bears dorsally curved auxiliary spines in at least three sizes, alternating such that spines of the same size are never adjacent.
Gaëtan J.-M. Potin, Pénélope Claisse, Alexis Trébaol, Pierre Gueriau, Yu Wu, Stephen Pates, and Allison C. Daley. 2025. A New giant nektobenthic radiodont benthivore from the Early Ordovician Fezouata Biota in Morocco. Acta Palaeontologica Polonica. 70(4). 709-722. DOI: doi.org/10.4202/app.01278.2025



































