Xenusion auerswaldae is an early lobopodian known from three[1] specimens found in glacial erratics on the Baltic coast of Germany.[2] 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,[3] which was deposited in the Lower Cambrian (Upper Tommotian–Lower Atdabanian; Stages 2→3).[4] It is the oldest currently known lobopodian with soft body fossils.[5]
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.[2] 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.[6] There is presumably a spine on each body bump and faint transverse parallel striations on the annulations on the legs.[2][6] 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,[2] but this also suggested to be a preservational artefact.[7]
Xenusion has been reinterpreted as an Ediacaran frond animal by Tarlo, and a drawing of that interpretation has been presented by McMenamin.[8] In a photograph presented in The Treatise on Invertebrate Paleontology Volume O, the organism's appearance seems to support the original interpretation more. Further studies of Xenusiid close the possibility of a Rangeomorphy affinity.[2][6]
^ abcdeDzik, J.; Krumbiegel, G. N. (1989). "The oldest 'onychophoran' Xenusion: A link connecting phyla?". Lethaia. 22 (2): 169. doi:10.1111/j.1502-3931.1989.tb01679.x.
^Han, J.; Zhang, Z. -F.; Liu, J. -N. (2008). "A preliminary note on the dispersal of the Cambrian Burgess Shale-type faunas". Gondwana Research. 14 (1–2): 269–276. doi:10.1016/j.gr.2007.09.001.
^RAMSKÖLD, L. and CHEN, J.-Y. 1998. Cambrian lobopodians: morphology and phylogeny. In EDGECOMBE, G. D. (ed.) Arthropod Fossils and Phylogeny, Columbia University Press, New York, 107–150 pp.
