Biology:Onychodictyon

Onychodictyon is a genus of extinct lobopodian known from the Lower Cambrian Chengjiang Maotianshan Shales in the Yunnan Province in China. It was characterized by a stout body covered by fleshy papillae and pairs of sclerotized plates with spines, representing part of the diverse "armoured lobopodians" alongside similar forms such as Microdictyon and Hallucigenia.

Discovery and naming

Onychodictyon is represented by two species: O. ferox from the Chengjiang Biota, and possibly O. spiniferum from Siberia (similar fossils known from Greenland are left in open taxonomy as Onychodictyon sp.), though some consider these synonymous. The species O. gracilis was erected in 2008 based on 3 specimens, which were later confirmed to belong to O. ferox.

Description

The maximum length of Onychodictyon is 70 mm (2.8 in). It has a resemblance to Microdictyon (net-like sclerite ornament) but also Aysheaia and tardigrades (basally-fused terminal leg pairs). Each leg has a pair of curved claws that are thought to have aided Onychodictyon in climbing onto other organisms. By having a unique anterior end structure, Onychodictyon may have been a deposit feeder which means that they would scavenge for organic material from the seafloor. Onychodictyon sclerites appear to have molted with some specimens exhibiting perfectly conjoined plates from successive molts.

Classification

The slightly simplified cladogram below is from a paper by Knecht et al. redescribing the lobopodian Palaeocampa anthrax.

†Diania 80px       †Lenisambulatrix 80px         †Paucipodia 80px       †Thanahita 80px     †Eoconchariidae   †Microdictyon 80px     †Fusuchoncharium     †Quadratapora           †Xenusion 70px     †Onychodictyon 80px         †Strictocorniculum     †Rhombocorniculum     †Orstenotubulus90px     †Carbotubulus     †Hallucigenia fortis     †Hallucigenia sparsa 60px       †"Hallucigenia" hongmeia       †Cardiodictyon 80px       Tardigrada (tardigrades) 60px   †Luolishaniida     †Ovatiovermis 60px     †Facivermis 70px         †Luolishania 80px   †Collinsovermidae   †EBS Collinsovermid (SAM P14848)       †Acinocricus       †Collinsovermis 80px       †Collinsium 90px     †Entothyreos 60px                                 †Aysheaiidae   †Aysheaia 80px       Soom Shale lobopodian (C1947)       †Hadranax 80px     †Palaeocampa 80px         Antennopoda     †Antennacanthopodia 80px   Onychophora   †Antennipatus     †Cretoperipatus 80px     †Helenodora 90px     Living onychophorans 80px   (velvet worms)     †Siberiidae   †Siberion 80px     †Megadictyon 80px     †Jianshanopodia 80px           †Pambdelurion 80px     †Kerygmachelidae 80px         †Opabiniidae 80px       †Radiodonta (e.g. Anomalocaris) 80px     Deuteropoda (modern arthropods) 70px

References

Template:Lobopodia Wikidata ☰ Q3882788 entry