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{{Short description|Cambrian fossil genus of chordate}}
{{italic title}}
{{Taxobox
| name = ''Metaspriggina''
| fossil_range = {{Fossil range|Middle Cambrian}}
| image = Metaspriggina_and_Maripolia.png
| image_caption = An artist's concept of '''''Metaspriggina''''' based on Conway Morris, Caron.<ref name="ConwayMorrisCaron2014">{{cite journal |last1=Conway Morris |first1=Simon |author-link1=Simon Conway Morris |last2=Caron |first2=Jean-Bernard |date=June 11, 2014 |title=A primitive fish from the Cambrian of North America |journal=[[Nature (journal)|Nature]] |location=London |publisher=[[Nature Publishing Group]] |doi=10.1038/nature13414 |issn=0028-0836 |volume=512 |issue=7515 |pages=419–422 |pmid=24919146|bibcode=2014Natur.512..419M |s2cid=2850050 }}</ref>
| regnum = [[Animalia]]
| phylum = [[Chordata]]
| infraphylum = [[Agnatha]]?
| familia = {{extinct}}'''Metaspriggiidae'''
| familia_authority = Simonetta & Insom 1993
| genus = {{extinct}}'''''Metaspriggina'''''
| genus_authority = Simonetta & Insom 1993
| binomial = {{extinct}}'''''Metaspriggina walcotti'''''
| binomial_authority = Simonetta & Insom 1993<ref>{{cite book| last = Van der Laan| first = Richard| title = Family-group names of fossil fishes| year = 2016| doi= 10.13140/RG.2.1.2130.1361| url= https://www.researchgate.net/publication/317888989}}</ref><ref>{{cite web | website=Collection of genus-group names in a systematic arrangement | title=Part 7- Vertebrates | url=http://mave.tweakdsl.nl/tn/genera7.html | display-authors=etal | access-date=30 June 2016 | archive-url=https://web.archive.org/web/20161005114629/http://mave.tweakdsl.nl/tn/genera7.html | archive-date=5 October 2016 | url-status=dead }}</ref>
}}

'''''Metaspriggina''''' is a [[genus]] of [[chordate]] initially known from two specimens in the [[Cambrian|Middle Cambrian]] [[Burgess Shale]]<ref name="ConwayMorris2008">{{cite journal |last=Conway Morris |first=Simon |date=March 2008 |title=A Redescription of a Rare Chordate, ''Metaspriggina walcotti'' Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada |journal=[[Journal of Paleontology]] |location=Boulder, CO |publisher=[[Paleontological Society|The Paleontological Society]] |volume=82 |issue=2 |pages=424–430 |doi=10.1666/06-130.1 |bibcode=2008JPal...82..424M |s2cid=85619898 |issn=0022-3360 }}</ref> and 44 specimens found in 2012 at the [[Marble Canyon (Canadian Rockies)|Marble Canyon]] bed in [[Kootenay National Park]].<ref name="ConwayMorrisCaron2014" />
[[File:Metaspriggina NT small.jpg|thumb|left|Life reconstruction of ''Metaspriggina walcotti'']]

[[File:Metaspriggina.png|thumbnail|left|Reconstruction of ''Metaspriggina'' based on the Burgess Shale specimens available in 2009.<ref name="ConwayMorris2008" /><ref name="royalonta">{{Cite web|date=2011|title=''Metaspriggina walcotti''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=81|archive-url=https://web.archive.org/20201112025257/http://burgess-shale.rom.on.ca/en/fossil-gallery/view-species.php?id=81|archive-date=2020-11-12|url-status=dead}}</ref>]]

[[File:Metaspriggina.jpg|thumb|The ''Metaspriggina'' fossil.]]

Whilst named after the [[Ediacara biota|Ediacaran organism]] ''[[Spriggina]]'', later work has shown the two to be unrelated.<ref name="ConwayMorris2008" /> ''Metaspriggina'' is considered to represent a primitive [[Cambrian chordate|chordate]], possibly transitional between [[cephalochordate]]s and the earliest [[vertebrate]]s, albeit this has been questioned because it seems to possess most of the characteristics attributed to [[craniate]]s. It lacked [[fin]]s and had a weakly developed [[Skull|cranium]], but it did possess two well-developed, upward-facing [[eye]]s with [[nostril]]s behind them.

''Metaspriggina'' also possessed a [[notochord]], along with seven pairs of pharyngeal bars, possibly made of [[cartilage]]. Surprisingly, they were not formed from a singular bone, but they were formed of multiple separate pairs of bones, along with first two of them that were enlarged compared to the others and that seemed to not support any gills, all of these characteristics suggesting a "distant link to [[gnathostomata]]ns". The largest specimens are {{convert|10|cm|in}} in length. Originally believed to be free-swimming but occasionally found on the [[Seabed|sea floor]],<ref name="royalonta"/><ref>{{cite book |last1=Smith |first1=M. Paul |last2=Sansom |first2=Ivan J. |last3=Cochrane |first3=Karen D. |year=2001 |chapter=The Cambrian origin of vertebrates |editor-last=Ahlberg |editor-first=Per Erik |editor-link=Per E. Ahlberg |title=Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny, Genetics and Development |url=https://archive.org/details/majoreventsearly00ahlb |url-access=limited |location=London; New York |publisher=[[Taylor & Francis]] |pages=[https://archive.org/details/majoreventsearly00ahlb/page/n81 67]–84 |isbn=0-415-23370-4 |lccn=00062919 |oclc=51667292}}</ref> the fossils from Marble Canyon showing the presence of eyes and their placement suggests it lived as a filter-feeder swimming above the sea floor.

The exceptional preservation at Marble Canyon also preserved muscle detail, showing that the animal moved with a side-to-side swimming motion.<ref name="ConwayMorrisCaron2014" /> In ''Metaspriggina'', the myomeral configuration has an additional ventral chevron, and a clear dorsal bend which defines a W-shaped arrangement that is directly comparable to fish.<ref name="ConwayMorrisCaron2014" />

The discovery of [[pharyngeal slit|pharyngeal bars]] (gill bars) makes ''Metaspriggina'' the oldest known animal to have this feature.<ref name="ConwayMorrisCaron2014" /> The first pair of pharyngeal bars later evolved to form the upper and lower [[jaw]]s of vertebrates. The second pair evolved to form the [[hyoid arch]]. In vertebrates this supports the jaws and the [[hyoid bone]] anchors the base of the tongue.

The discovery of ''Metaspriggina'' makes the origins of gnathostomatans a little more confusing, as it was roughly contemporary with ''[[Pikaia]]''. As ''Pikaia'' did not have gill bars, unlike ''[[Branchiostoma]]'',<ref name=":0">{{Cite web|url=https://www.geol.umd.edu/~tholtz/G331/lectures/331chordata.html|title=GEOL 331 Principles of Paleontology|website=www.geol.umd.edu|access-date=2018-01-06}}</ref> there are two possible explanations for this. One is that the [[Chordate]] phylum split in four before ''Metaspriggina'' lived, with ''Metaspriggina'' and the other craniates (both gnathostomatans and [[Agnatha]]) grouped with ''Branchiostoma'' and the cephalochordates, and ''Pikaia'' out on a side branch. ''Metaspriggina'' is here a direct ancestor of all gnathostomatans, with the Agnatha the most closely related group. In this explanation, ''Pikaia'' is not a close relative of [[Craniate]]s at all, nor of cephalochordates, but something even more primitive, and the defining feature of the craniate-cephalochordate group is their gill bars.

The other explanation is that ''Metaspriggina'' was the ancestor of all gnathostomatans, again closely related to the Agnatha to form the Chordata. However, instead of being a very primitive relative, ''Pikaia'' was the ancestor of all cephalochordates, and the gill bars evolved convergently in them somewhere between ''Pikaia'' and ''Branchiostoma.'' This might explain why ''Branchiostoma'' has such a different number of gill bars to chordates (or at least their embryos).<ref name=":0" />
Considering that [[Conodont|conodonts]], the teeth elements of a type of extinct fish belonging to the Agnatha, are already found in Cambrian stage 2 (521-529 MA BP), some 20 million years before the Burgess shale, this latter explanation does not stand. The split between Agnatha and other chordates must therefore have happened earlier, during Cambrian stage 1 or even Ediacaran times.

Phylogenetic analysis suggests that ''Metaspriggiidae'' are "stem-vertebrates" along with ''[[Haikouella]]'' and the [[Myllokunmingiidae|Myllokunmingiids]] leading to the [[Crown group|crown]] [[vertebrates]], who divided themselves into two main directions: jawless fishes like [[conodonts]] leading to the [[extant cyclostomes|Cyclostomi]], and jawless fishes like the [[Cephalaspidomorph]] who developed armors and jaws to become the [[gnathostomes]].<ref>{{cite journal |first1=Tetsuto |last1=Miyashita |first2=Michael I. |last2=Coates |first3=Robert |last3=Farrar |first4=Peter |last4=Larson |first5=Phillip L. |last5=Manning |first6=Roy A. |last6=Wogelius |first7=Nicholas P. |last7=Edwards |first8=Jennifer |last8=Anné |first9=Uwe |last9=Bergmann |first10=A. Richard |last10=Palmer |first11=Philip J. |last11=Currie |display-authors=6 |year=2019 |title=Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=116 |issue=6 |pages=2146–2151 |doi=10.1073/pnas.1814794116 |pmid=30670644 |pmc=6369785|bibcode=2019PNAS..116.2146M |doi-access=free }}</ref>

== See also ==
*[[Paleobiota of the Burgess Shale]]
==References==
{{Reflist}}

== External links ==
*{{Cite web|date=2011|title=''Metaspriggina walcotti''|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=https://burgess-shale.rom.on.ca/fossils/metaspriggina-walcotti/}}
*{{cite web |url=http://www.cam.ac.uk/research/news/new-fossil-find-pinpoints-the-origin-of-jaws-in-vertebrates |title=New fossil find pinpoints the origin of jaws in vertebrates |author= |date=June 11, 2014 |website=Research at Cambridge: News |publisher=[[University of Cambridge]] |location=Cambridge, England |access-date=2014-06-13}}

{{Taxonbar|from=Q140492}}

[[Category:Cambrian chordates]]
[[Category:Burgess Shale fossils]]
[[Category:Prehistoric jawless fish genera]]
[[Category:Cambrian genus extinctions]]

Metaspriggina - Revision history

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