Nectocaris

Nectocaris pteryx Temporal range: Middle Cambrian, 505 Ma PreЄ Є O S D C P T J K Pg N ↓
Current reconstruction of Nectocaris, based on 92 specimens. Dorso-ventrally preserved specimens demonstrated that the fins were lateral, and the additional material indicated that the feature originally interpreted as an arthropod head-shield was in fact a nozzle-like appendage, which has been interpreted as a funnel.
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca (?)
Stem-group:	Cephalopoda (?)
Family:	†Nectocarididae
Genus:	†Nectocaris Conway Morris, 1976
Species:	†N. pteryx
Binomial name
Nectocaris pteryx Conway Morris, 1976

Nectocaris pteryx is a species of possible cephalopod^[1] or arthropod^[2] affinity, known from the Middle Cambrian Burgess Shale.

Nectocaris was a free-swimming, predatory or scavenging organism, possibly occupying a niche similar to the arrow worms.^[3] This lifestyle is honoured in its binomial name: Nectocaris means "swimming shrimp" (from the Ancient Greek νηκτόν, nekton, meaning "swimmer" and καρίς, karis, "shrimp"; πτέρυξ, pteryx, means "wing").

History of study

Original reconstruction based on a single, incompletely preserved, lateral specimen. The author of this reconstruction, based on the material then available, considered Nectocaris to bear arthropod and chordate-like features.

Charles Doolittle Walcott, the discoverer of the Burgess Shale, had photographed the one specimen he had collected in the 1910s, but never had time to investigate it further. As such, it was not until 1976 that Nectocaris was formally described, by Simon Conway Morris.^[4]

The head had two stalked eyes,^[4] one pair of tentacles, and a flexible siphon underneath its body.^[1] Fleshy fins supported by internal spines ran along the sides of the flattened, kite-shaped body.^[1] Because the genus was only known from a single specimen with no counterpart,^[5] Conway Morris was unable to deduce its affinity. It had some features which were reminiscent of the arthropods, but these could well have been convergently derived.^[4][6] Its fins were very unlike the arthropods.^[4]

Working from photographs, the Italian palaeontologist Alberto Simonetta believed he could classify Nectocaris within the chordates.^[7] He focussed mainly on the tail and fin morphology, interpreting Conway Morris's 'gut' as a notochord – a distinctive chordate feature.^[7]

The classification of Nectocaris was revisited in 2010, when Martin Smith and Jean-Bernard Caron described 91 additional specimens, many of them better preserved than the type. These allowed them to reinterpret Nectocaris as a primitive cephalopod, with two tentacles instead of the 8 or 10 of modern cephalopods. The structure previous researchers had identified as an oval carapace or shield behind the eyes^[3] was suggested to be a soft funnel, similar to the ones used for propulsion by modern cephalopods. The interpretation would push back the origin of cephalopods by at least 30 million years, much closer to the first appearance of complex animals, in the Cambrian explosion, and implied that – against the widespread expectation – cephalopods evolved from non-mineralized ancestors.^[1]

A later analysis claimed to undermine the cephalopod interpretation, stating that it did not square with the established theory of cephalopod evolution.^[2] According to these authors, Nectocaris is best treated as a member incertae sedis of the arthropod group Dinocaridida (which includes the anomalocaridids), but they stopped short of formally changing the classification.^[2] However, it is straightforward to demonstrate that an anomalocaridid affinity is not supported.^[8][9] Other studies have yet to put forwards a more plausible affinity.^[10][9]

References

1. ^ ^{a b c d} Martin R. Smith & Jean-Bernard Caron (2010). "Primitive soft-bodied cephalopods from the Cambrian". Nature 465 (7297): 469–472. Bibcode 2010Natur.465..469S. doi:10.1038/nature09068. PMID 20505727. http://individual.utoronto.ca/martinsmith/nectocaris.html. 
2. ^ ^{a b c} Dawid Mazurek & Michał Zatoń (2011). "Is Nectocaris pteryx a cephalopod?". Lethaia 44 (1): 2–4. doi:10.1111/j.1502-3931.2010.00253.x. 
3. ^ ^{a b} Simon Conway Morris (1989). "Burgess Shale faunas and the Cambrian Explosion". Science 246 (4928): 339–346. Bibcode 1989Sci...246..339C. doi:10.1126/science.246.4928.339. PMID 17747916. http://www.sciencemag.org/cgi/content/abstract/246/4928/339. 
4. ^ ^{a b c d} Simon Conway Morris (1976). " Nectocaris pteryx, a new organism from the Middle Cambrian Burgess Shale of British Columbia". Neues Jahrbuch für Geologie und Paläontologie, Monatshefte 12: 703–713. 
5. ^ Stephen Jay Gould (1989). Wonderful Life: The Burgess Shale and the Nature of History. Hutchison Radius. ISBN 0091742714. 
6. ^ Waggoner, B. M. (1996). "Phylogenetic Hypotheses of the Relationships of Arthropods to Precambrian and Cambrian Problematic Fossil Taxa". Systematic Biology 45 (2): 190–222. doi:10.2307/2413615. JSTOR 2413615.  edit
7. ^ ^{a b} Alberto M. Simonetta (1988). "Is Nectocaris pteryx a chordate?". Bollettino di Zoologia 55 (1–2): 63–68. doi:10.1080/11250008809386601. 
8. ^ Smith, M. R.; Caron, J.-B. (2011). "Nectocaris and early cephalopod evolution: Reply to Mazurek & Zatoń". Lethaia: no-no. doi:10.1111/j.1502-3931.2011.00295.x.  edit
9. ^ ^{a b} Runnegar, B. (2011). "Once again: Is Nectocaris pteryx a stem-group cephalopod?". Lethaia 44 (4): 373. doi:10.1111/j.1502-3931.2011.00296.x.  edit
10. ^ B. Kröger, J. Vinther & D. Fuchs (2011). "Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules". BioEssays 33 (8): 602–613. doi:10.1002/bies.201100001. 

Further reading

Paleontology portal

• The taxonomy and history of Nectocaris are discussed by Brian Switek on his blog entry: Brian Switek (July 5, 2011). "Nectocaris: What the heck is this thing?". Laelaps. http://www.wired.com/wiredscience/2011/07/nectocaris-what-the-heck-is-this-thing/. 
• BBC News coverage of the Smith & Caron's original redescription is presented here: Katia Moskvitch (May 27, 2010). "Mystery fossil is ancestor of squid". BBC News. http://news.bbc.co.uk/1/hi/science_and_environment/10173293.stm. 
• A blog article supporting Mazurek & Zatoń's view is presented here: Christopher Taylor (January 14, 2011). "So nice when people agree with you". Catalogue of Organisms. http://coo.fieldofscience.com/2011/01/so-nice-when-people-agree-with-you.html. 
• Conway Morris, S. (1997). The Crucible of Creation: the Burgess Shale and the rise of animals. Oxford University Press. ISBN 0–19–286202–2. 

External links

• Media related to Nectocaris at Wikimedia Commons