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Abstract
AbstractThe classification of Radiodonta is primarily based on the morphology of their frontal appendages, a main feeding structure of this iconic group of mostly Cambrian stem‐group euarthropods. However, recent progress in the description and revision of radiodont taxa, particularly drawing on their frontal appendages, has exposed morphological variation that challenges reliable identification of higher‐level groupings. Here we describe a new taxon of Radiodonta, Laminacaris chimera gen. et sp. nov., from the Cambrian Series 2, Stage 3, Chengjiang biota of China, based on its unique frontal appendage morphology. Laminacaris is distinctive for its combination of characters shared by hurdiids and other early Cambrian radiodont families. Elongated, possibly unpaired endites on two proximal podomeres that bear small distally‐directed auxiliary spines oriented perpendicular to the long axis of the endite, are comparable with the elongated endites and their auxiliary spines of all known Cambrian members of Hurdiidae. In contrast, endites on more distal podomeres are similar to some species of Anomalocaris, and the dorsal spines at the distal end resemble those of Amplectobelua. The mosaic characters in the frontal appendage of Laminacaris chimera may capture morphology close to the divergence between the major radiodont groups.
Highlights
Radiodonta Collins 1996, putative stem-group Euarthropoda, is represented worldwide by over 25 species reported from Cambrian Series 2 to at least the Ordovician and likely the Early Devonian
We describe a new taxon from the Chengjiang biota showing a unique mix of frontal appendage characters, of which the elongated endites bearing auxiliary spines confined to one side are shared with Hurdiidae
The major difference between these two taxa is that Ramskoeldia has gnathobase-like structures similar to those seen in Amplectobelua and mouthparts made up of smooth and tuberculate plates (Cong et al 2018) whereas Anomalocaris canadensis has a triradial oral cone and no gnathobase-like structures have been recognized (Daley & Bergström 2012; Daley & Edgecombe 2014)
Summary
Radiodonta Collins 1996, putative stem-group Euarthropoda, is represented worldwide by over 25 species reported from Cambrian Series 2 to at least the Ordovician and likely the Early Devonian. As the earliest active large predators in the animal fossil record, most radiodonts used paired frontal appendages to capture and subdue prey. These frontal appendages are segmented structures bearing numerous spines, attached to the ventral surface of the head, anterolateral to the mouth and associated oral structures. Frontal appendages are important structures for understanding radiodont taxonomy, because many species are known only from isolated frontal appendages, such as Amplectobelua stephenensis Daley & Budd, 2010, Anomalocaris pennsylvanica Resser, 1929, Caryosyntrips serratus Daley & Budd, 2010, C. camurus Pates & Daley, 2017, C. durus Pates & Daley, 2017, Peytoia infercambriensis (Lendzion, 1975), Stanleycaris hirpex Pates et al, 2018a, and Tamisiocaris borealis Daley & Peel, 2010. Phylogenetic analyses of radiodont interrelationships have focused primarily on frontal appendage characters (Vinther et al 2014), with four putative clades recovered, namely Anomalocarididae Raymond, 1935, Amplectobeluidae Vinther et al, 2014, Hurdiidae Vinther et al, 2014, and ‘Cetiocaridae’, each of which has a distinctive frontal appendage morphology (e.g. Cong et al 2018)
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