Xenusion

Xenusion auerswaldae is an early lobopodian known from two specimens found in glacial erratics on the Baltic coast of Germany.[1] They probably originated in the Kalmarsund Sandstone of Southern Sweden,[2] which was deposited in the Lower Cambrian (Upper Tommotian–Lower Atdabanian; Stages 2→3).[3] It is the oldest currently known lobopodian with soft body fossils.[4]

Xenusion auerswaldae
Temporal range:
Fossil specimen
Life restoration
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
(unranked): Panarthropoda
Phylum: †"Lobopodia"
Class: †Xenusia
Order: †Protonychophora
Family: †Xenusiidae
Genus: †Xenusion
Pompeckj, 1927
Species:
†X. auerswaldae
Binomial name
†Xenusion auerswaldae
Pompeckj, 1927

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.[1] 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.[5] There is presumably a spine on each body bump and faint transverse parallel striations on the annulations on the legs.[1][5] The legs of what is possibly the foremost segments are either absent or not preserved. The head is believed to be missing or is poorly preserved. Based on a new specimen that showing the anterior section, it possibly have a long narrow proboscis.[1] but this also suggested to be a preservational artefact.[6]

Xenusion has been reinterpreted as an Ediacaran frond animal by Tarlo, and a drawing of that interpretation has been presented by McMenamin.[7] 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.[1][5]

References
  1. Dzik, 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.
  2. Jaeger, Hermann; Martinsson, Anders (1967-01-31). "Remarks on the Problematic Fossil Xenusion Auerswaldae". Geologiska Föreningen i Stockholm Förhandlingar. 88 (4): 435–452. doi:10.1080/11035896709455501. ISSN 0016-786X.
  3. 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.
  4. Ou, Qiang; Mayer, Georg (2018-09-20). "A Cambrian unarmoured lobopodian, †Lenisambulatrix humboldti gen. et sp. nov., compared with new material of †Diania cactiformis". Scientific Reports. 8 (1): 13667. Bibcode:2018NatSR...813667O. doi:10.1038/s41598-018-31499-y. ISSN 2045-2322. PMC 6147921. PMID 30237414.
  5. Liu, Jianni; Dunlop, Jason A. (2014-03-15). "Cambrian lobopodians: A review of recent progress in our understanding of their morphology and evolution". Palaeogeography, Palaeoclimatology, Palaeoecology. Cambrian Bioradiation. 398: 4–15. Bibcode:2014PPP...398....4L. doi:10.1016/j.palaeo.2013.06.008. ISSN 0031-0182.
  6. 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.
  7. McMenamin, Mark A. S. (1986). "The Garden of Ediacara". PALAIOS. 1 (2): 178–182. doi:10.2307/3514512. ISSN 0883-1351. JSTOR 3514512.
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