Metaspriggina
| Metaspriggina Temporal range: Burgess Shale | |
|---|---|
 | |
| An artist's concept of Metaspriggina based on Conway Morris, Caron.[1] | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Family: | Metaspriggiidae |
| Genus: | Metaspriggina |
| Species: | M. walcotti |
| Binomial name | |
| Metaspriggina walcotti | |
Metaspriggina is a genus of chordate initially known from two specimens in the Middle Cambrian Burgess Shale[2] and 44 specimens found in 2012 at the Marble Canyon bed in Kootenay National Park.[1]
Whilst named after the Ediacaran organism Spriggina, later work has shown the two to be unrelated.[2] Metaspriggina is considered to represent a primitive chordate, possibly transitional between cephalochordates and the earliest vertebrates, albeit this has been questioned because it seems to possess most of the characteristics attributed to craniates. It lacked fins and it had a weakly developed cranium, but it did possess two well-developed upward-facing eyes with nostrils 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 gnathostomatans". The largest specimens are 10 centimetres (3.9 in) in length. Originally believed to be free-swimming but occasionally found on the sea floor,[3][4] 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.[1] 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.[1]
The discovery of pharyngeal bars (gill bars) makes Metaspriggina the oldest known animal to have this feature.[1] The first pair of pharyngeal bars later evolved to form the upper and lower jaws of vertebrates.
References
- 1 2 3 4 5 Conway Morris, Simon; Caron, Jean-Bernard (June 11, 2014). "A primitive fish from the Cambrian of North America". Nature. London: Nature Publishing Group. 512: 419–422. ISSN 0028-0836. PMID 24919146. doi:10.1038/nature13414. Retrieved 2014-06-13.
- 1 2 3 Conway Morris, Simon (March 2008). "A Redescription of a Rare Chordate, Metaspriggina walcotti Simonetta and Insom, from the Burgess Shale (Middle Cambrian), British Columbia, Canada". Journal of Paleontology. Boulder, CO: The Paleontological Society. 82 (2): 424–430. ISSN 0022-3360. doi:10.1666/06-130.1. Retrieved 2014-06-13.
- 1 2 "Metaspriggina walcotti". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011.
- ↑ Smith, M. Paul; Sansom, Ivan J.; Cochrane, Karen D. (2001). "The Cambrian origin of vertebrates". In Ahlberg, Per Erik. Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny, Genetics and Development. London; New York: Taylor & Francis. pp. 67–84. ISBN 0-415-23370-4. LCCN 00062919. OCLC 51667292.
External links
- "Metaspriggina walcotti". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011.
- "New fossil find pinpoints the origin of jaws in vertebrates". Research at Cambridge: News. Cambridge, England: University of Cambridge. June 11, 2014. Retrieved 2014-06-13.