A Burgess Shale mandibulate arthropod with a pygidium: a case of convergent evolution

• DOI: 10.1002/spp2.1366
• Publication Date: 2021-06-15T09:27:52Z
• Authors: Alejandro Izquier...; Jean‐Bernard Caron
• Keywords: Rostrum; Arthropod; Trilobite; Appendage; Convergent evolution

Abstract Cambrian bivalved arthropods are a polyphyletic group of carapace‐bearing that includes stem euarthropods, mandibulates and crustaceans. Here, we describe Pakucaris apatis gen. et sp. nov., new mandibulate arthropod from the middle (Wuliuan Stage) Burgess Shale (Marble Canyon, Kootenay National Park, British Columbia, Canada). Two morphotypes this small (11.6–26.6 mm long) recognized, which differ mainly in their size number segments, possibly reflecting sexual dimorphism or different anamorphic stages. The carapace presents dorsal crest extending anteriorly into recurved rostrum two anterolateral processes. Around 20% posteriormost body segments limbs covered by large spine‐bearing shield. head bears pair eyes, possible unsegmented appendicular projections pairs segmented appendages. thorax is multisegmented, homonomous, with weakly sclerotized bearing biramous limbs, composed stenopodous endopod c . 20 podomeres paddle‐shaped exopod. interpreted as nektobenthic suspension feeder. Bayesian phylogenetic analysis implies position within Hymenocarina mandibulates. posterior shield regarded pygidium, represents case morphofunctional convergent evolution between mandibulates, artiopodans mollisoniids. Furthermore, adds to growing pygidium‐bearing arthropods, potentially hinting at common developmental pattern across early evolution. This study not only increases our understanding but also illustrates unique evolutionary convergence during Explosion.