Cambrian Lobopods: Comparisons and Evolutionary Significance  

Knowledge of Cambrian lobopods has increased dramatically since the description of Aysheaia pedunculata from the Burgess Shale in the last century, and sixteen genera (twenty-one species) of lobopods displaying diverse morphologies are currently recognized from Early and Middle Cambrian lagerstätte deposits.  Lobopods are now considered to be possible ancestors to the arthropods.  Intermediate forms, such as Miraluolishania, possess a mosaic of both lobopod and arthropod characters, lending support to this hyposthesis.  The lobopod features of Miraluolishania are its worm-like body design, dorsal spines, and non-segmented limbs or lobe-like legs; arthropod features include primary cephalization with paired eyes, paired antennae, and incipient tagmosis.  Jianshanopodia, a large form with complex branched appendages, may throw new light on the origin of biramous limbs.  Megadictyon cf.  haikouensis had a head bearing caecae-like structures resembling those of the arthropod Naraoia and some chelicerates, and bore ‘Peytoia’-like mouthparts and frontal appendages.  The latter features are similar to those of the AOPK (Anomalocaris-Opabinia-Pambdelurion-Kerygmachela) group.  Thus, Cambrian lobopods exhibit a much wider morphological diversity than extant onychophorans, and present evidence suggests that frontal appendages are homologous features that appear deep in the lobopod-arthropod phylogeny. 

As members of the Ecdysozoa, lobopods are also regarded as having affinities with priapulids.  Dzik and Krumbiegel hypothesize an origin from priapulid-palaeoscolecid-like worms through the development of segments and limbs.  In lobopod evolution, whatever the origin, the mode of life changed from priapulid burrowing to lobopod-style crawling.  Complete specimens of Facivermis yunnanicus, showing both priapulid and arthropod characters, provide strong support for this proposed affinity.