Amiskwiais a genus of soft-bodiedanimalsknown fromfossilsof the MiddleCambrianLagerstätten both in theBurgess ShaleinBritish Columbia,Canada and theMaotianshan shalesofYunnanProvince, China. It is interpreted as a member of the cladeGnathiferasensu lato[1]or as a basalcucullophoran.[2][3][4]
| Amiskwia Temporal range:
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| Fossil ofAmiskwia sagittiformisfrom theBurgess Shale | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Clade: | Cucullophora |
| Genus: | †Amiskwia Walcott, 1911 |
| Type species | |
| Amiskwia sagittiformis Walcott, 1911
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| Species | |
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Etymology
editThe scientific nameAmiskwia sagittiformisderives from the Creeamiskwi,"beavertail", a name of various objects in Yoho National Park, and from the Latinsagitta( "arrow" ) andformis( "shape" ), in reference to the general appearance of the animal. "Sinica", ofA. sinica,refers to that species' origin from China.
Description
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Known specimens ofAmiskwiavary in length from 7.4 to 31.3 millimetres (0.29 to 1.23 in) and in width from 0.5 to 5.5 millimetres (0.020 to 0.217 in). The body was somewhat flattened. The head had a pair of tentacles that emerged from the midline of the head. The tentacles had a relatively thick base and tapered to a point. Along the sides of the trunk were a pair of lateral fins, which were around one third of the total body length. The trunk terminated with a flat, rounded caudal fin. The gut was straight, and ran from the mouth to the anus, which was located on the underside of the body near the caudal fin. Within the mouth is a pair of semi-circular structures, described as "jaws" each bearing 8-10 conical spikes, which increased in size away from the midline of the structure. Two other structures, dubbed the "dorsal plate" and "ventral plate", are also present in the mouth.[1]
Phylogeny
editThe followingdendrogramshows the evolutionary relationships ofAmiskwiaas in Park et al. 2024.[4]
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- aA yet undescribed chaetognath, as of January 2024, fromSirius Passet
Ecology
editAmiskwiawas likely a freely swimming (nektonic) organism that was either a predator or a scavenger.[1]
History of research
editAmiskwiawas originally categorized bypaleontologistCharles Walcott.Walcott thought he saw three buccal spines in the fossils, and therefore categorizedAmiskwiaas achaetognathworm (arrow worm). However,Amiskwiaappears to lack the characteristic grasping spines and teeth of other Burgess fossil arrow worms. Later scientists suggested an affinity with thenemerteans(ribbon worms), but the evidence for this was somewhat inadequate.[5]Conway Morris,on re-examining of the Burgess Shale fauna in the 1970s, described it as being the single known species in an otherwise unknownphylum,given that it has two tentacles near its mouth, rather than the characteristic single tentacle of true nemerteans. (Nemerteans do not have a single tentacle. However, a pair of antero-lateral tentacles is present in two of the many genera of pelagic nemerteans. Nemerteans do have a single eversible—normally internal—proboscis, which when everted could resemble an anterior median tentacle if fossilized. Whether retracted or everted, the proboscis is the only structure in pelagic nemerteans likely to fossilize, as it is the only structure with substantial connective tissue and muscle. The body wall has almost no muscle or connective tissue and is exceedingly unlikely to fossilize; hence, a pelagic nemertean fossil would be only the proboscis).[5]Butterfieldimplies from the appearance of the fossils that the organisms may have lacked a cuticle:[6]while this is also true of the nemerteans, these organisms lack acoelomand are thus unlikely to fossilise. He goes on to argue that the absence of cuticle is characteristic of thechaetognaths;whilst teeth would be expected, a similar fossil,Wiwaxia,shows such structures in only 10% of the expected instances, andanomalocarididsare often found detached from their mouthparts, so the absence may be taphonomic rather than genuine. The absence of spines could simply mean that the fossils represent young organisms — or that later chaetognath evolution involvedpaedomorphosis.[7]
Two studies published in 2019 redescribedAmiskwia.Vinther and Parry (2019) argued thatAmiskwiawas a stem-group chaetognath,[2]while Caron and Cheung (2019) suggested that the organism was a total groupgnathiferan,based on the presence of gnathiferan-like jaws and ventral plates within the mouth. Its precise affinity within this group is difficult to resolve, they suggested that if it fell in the stem lineage of any extant phylum then it would be agnathostomulid.[1]A 2022 study supported a stem-chaetognath interpretation, suggesting that gnathiferan-like jaws were lost in the ancestor of chaetognaths.[3]A 2024 study again supported a stem-chaetognath position.[4]
See also
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References
edit- ^abcdCaron, Jean-Bernard; Cheung, Brittany (2019)."Amiskwia is a large Cambrian gnathiferan with complex gnathostomulid-like jaws".Communications Biology.2:164.doi:10.1038/s42003-019-0388-4.PMC6499802.PMID31069273.
- ^abVinther, Jakob; Parry, Luke A. (March 2019)."Bilateral Jaw Elements in Amiskwia sagittiformis Bridge the Morphological Gap between Gnathiferans and Chaetognaths".Current Biology.29(5): 881–888.e1.Bibcode:2019CBio...29E.881V.doi:10.1016/j.cub.2019.01.052.hdl:1983/51b1b6c1-0220-4469-977f-480e847a9101.PMID30799238.S2CID72332845.
- ^abBekkouche, Nicolas; Gąsiorowski, Ludwik (2022-12-31)."Careful amendment of morphological data sets improves phylogenetic frameworks: re-evaluating placement of the fossil Amiskwia sagittiformis".Journal of Systematic Palaeontology.20(1): 2109217.doi:10.1080/14772019.2022.2109217.ISSN1477-2019.S2CID252747552.
- ^abcPark, Tae-Yoon S.; Nielsen, Morten Lunde; Parry, Luke A.; Sørensen, Martin Vinther; Lee, Mirinae; Kihm, Ji-Hoon; Ahn, Inhye; Park, Changkun; De Vivo, Giacinto; Smith, M. Paul; Harper, David A. T.; Nielsen, Arne T.; Vinther, Jakob (2024)."A giant stem-group chaetognath".Science Advances.10(1): eadi6678.Bibcode:2024SciA...10I6678P.doi:10.1126/sciadv.adi6678.PMC10796117.PMID38170772.
- ^abConway Morris, S. (1977). "A redescription of the Middle Cambrian wormAmiskwia sagittiformisWalcott from the Burgess Shale of British Columbia ".Paläontologische Zeitschrift.51(3–4):271–287.Bibcode:1977PalZ...51..271M.doi:10.1007/BF02986576.ISSN0031-0220.S2CID84554285.
- ^Butterfield, N. J. (1 July 1990). "Organic Preservation of Non-Mineralizing Organisms and the Taphonomy of the Burgess Shale".Paleobiology.16(3):247–399.Bibcode:1990Pbio...16..272B.doi:10.1017/s0094837300009994.ISSN0094-8373.JSTOR2400788.S2CID133486523.
- ^Kasatkina, A. P. 1982. Ŝetinkočelustnyje morej SSSR i sopredel'nyh vod.
136 pp. Nauka, Leningrad.
- Cited inDoguzhaeva, L. A.; Mutvei, H.; Mapes, R. H. (2002)."Chaetognath grasping spines from the Upper Mississippian of Arkansas (USA)"(PDF).Acta Palaeontologica Polonica.47(3):421–430.Retrieved2007-08-19.
External links
edit- "Amiskwia sagittiformis".Burgess Shale Fossil Gallery.Virtual Museum of Canada. 2011. Archived fromthe originalon 2020-11-12.Retrieved2023-01-21.
- Graphic of Amiskwia in motion