Amiskwia
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''Amiskwia'' is a genus of soft-bodied marine
animal Animals are multicellular, eukaryotic organisms in the Biology, biological Kingdom (biology), kingdom Animalia (). With few exceptions, animals heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, ...
s known from
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s of the Middle
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
Lagerstätten both in the
Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...
in
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, Canada and the
Maotianshan shales The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...
of
Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...
Province, China. It is interpreted as a member of the clade Gnathifera ''sensu lato'' or as a basal cucullophoran.


Etymology

The scientific name ''Amiskwia sagittiformis'' derives from the Cree ''amiskwi'', "beavertail", a name of various objects in Yoho National Park, and from the Latin ''sagitta'' ("arrow") and ''formis'' ("shape"), in reference to the general appearance of the animal. "Sinica", of ''A. sinica'', refers to that species' origin from China.


Description

Known specimens of ''Amiskwia'' vary in length from and in width from . 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.


Phylogeny

The following
dendrogram A dendrogram is a diagram representing a Tree (graph theory), tree graph. This diagrammatic representation is frequently used in different contexts: * in hierarchical clustering, it illustrates the arrangement of the clusters produced by ...
shows the evolutionary relationships of ''Amiskwia'' as in Park et al. 2024. :A yet undescribed chaetognath, as of January 2024, from
Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...


Ecology

''Amiskwia'' was likely a freely swimming (nektonic) organism that was either a predator or a scavenger.


History of research

''Amiskwia'' was originally categorized by
paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...
Charles Walcott. Walcott thought he saw three buccal spines in the fossils, and therefore categorized ''Amiskwia'' as a
chaetognath The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic; however about 20% of the known species ...
worm (arrow worm). However, ''Amiskwia'' appears to lack the characteristic grasping spines and teeth of other Burgess fossil arrow worms. Later scientists suggested an affinity with the
nemertea Nemertea is a phylum of animals also known as ribbon worms or proboscis worms, consisting of about 1300 known species. Most ribbon worms are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. ...
ns (ribbon worms), but the evidence for this was somewhat inadequate. Conway Morris, on re-examining of the Burgess Shale fauna in the 1970s, described it as being the single known species in an otherwise unknown
phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
, 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). Butterfield implies from the appearance of the fossils that the organisms may have lacked a cuticle: while this is also true of the nemerteans, these organisms lack a
coelom The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, i ...
and are thus unlikely to fossilise. He goes on to argue that the absence of cuticle is characteristic of the
chaetognath The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, they are mostly pelagic; however about 20% of the known species ...
s; whilst teeth would be expected, a similar fossil, ''
Wiwaxia ''Wiwaxia'' is a genus of soft-bodied animals that were covered in carbonaceous scales and spines that protected it from predators. ''Wiwaxia'' fossils—mainly isolated scales, but sometimes complete, articulated fossils—are known from early C ...
'', shows such structures in only 10% of the expected instances, and
anomalocaridid Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a varie ...
s are 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 involved
paedomorphosis Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, physiological, or Somatic (biology), somatic, development of an organism, typically an animal. Neoteny i ...
.Kasatkina, A. P. 1982. Ŝetinkočelustnyje morej SSSR i sopredel'nyh vod. 136 pp. Nauka, Leningrad. :Cited in Two studies published in 2019 redescribed ''Amiskwia.'' Vinther and Parry (2019) argued that ''Amiskwia'' was a stem-group chaetognath, while Caron and Cheung (2019) suggested that the organism was a total group gnathiferan, 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 a
gnathostomulid Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956. ...
. A 2022 study supported a stem-chaetognath interpretation, suggesting that gnathiferan-like jaws were lost in the ancestor of chaetognaths. A 2024 study again supported a stem-chaetognath position.


See also

*
Paleobiota of the Burgess Shale This is a list of the Biota (ecology), biota of the Burgess Shale, a Cambrian lagerstätte located in Yoho National Park in Canada. The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is fa ...


References


External links

*
Graphic of Amiskwia in motion
{{Taxonbar, from1=Q15104428, from2=Q582764 Cambrian invertebrates Burgess Shale fossils Maotianshan shales fossils Chaetognatha Controversial taxa Cambrian genus extinctions