Biology:Xenusion

Xenusion auerswaldae is an early lobopodian known from three specimens found in glacial erratics on the Baltic coast of Germany. Another specimen, discovered shortly after the holotype, was briefly observed but soon went missing. Except for this lost specimen, the fossils probably originated in the Kalmarsund Sandstone of Southern Sweden, which was deposited in the Lower Cambrian (Upper Tommotian–Lower Atdabanian; Stages 2→3). It is the oldest currently known lobopodian with soft body fossils.

Description

The specimens are not especially well preserved. The older specimen is 10 cm or so in length with a narrow, weakly segmented body. Assuming it was the posterior section, the specimen was estimated to be part of an animal about 20 cm in length. A depression runs up the bottom on all but the rearmost segments. There is a slightly bulbous termination, and each segment before that seems to have a single pair of tapering annulated legs similar to the modern onychophoran, but without specialized feet and claws. More than 10 body segments were present. There is presumably a spine on each body bump and faint transverse parallel striations on the annulations on the legs. The legs of what is possibly the foremost segments are either absent or not preserved. The head is believed to be missing or poorly preserved. Based on a new specimen that shows the anterior section, it possibly had a long narrow proboscis, but this also suggested to be a preservational artefact.

Classification

While Xenusion has also been reinterpreted as an Ediacaran frond animal by Tarlo, as illustrated by McMenamin, this has not been accepted in subsequent works such as The Treatise on Invertebrate Paleontology and other publications. 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

External links

• Onychophora: Fossil Record

Template:Lobopodia Wikidata ☰ Q136421 entry