Nectocaris
Nectocaris Temporal range:
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Specimen ROM 60079 | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Family: | †Nectocarididae |
Genus: | †Nectocaris Conway Morris, 1976 |
Species: | †N. pteryx
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Binomial name | |
†Nectocaris pteryx Conway Morris, 1976
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Nectocaris is a genus of squid-like animal of controversial affinities known from the
Nectocaris was a free-swimming, predatory or scavenging organism. This lifestyle is reflected in its binomial name: Nectocaris means "swimming shrimp" (from the Ancient Greek νηκτόν, nekton, meaning "swimmer" and καρίς, karis, "shrimp"; πτέρυξ, pteryx, means "wing"). Two morphs are known: a small morph, about an inch long, and a large morph, anatomically identical but around four times longer.[1]
Nectocaridids have controversial affinities. Some authors have suggested that they represent the earliest known cephalopods. However, their morphology is strongly dissimilar to confirmed early cephalopods, and thus their affinities to cephalopods and even to molluscs more broadly are rejected by most authors.[2][3] Their affinities to any animal group beyond Bilateria are uncertain, though they have been suggested to be members of Lophotrochozoa.[3]
The closely related Ordovician taxon Nectocotis is a second genus, closely resembling Nectocaris, but suggested to have had an internal skeletal element.[4]
Anatomy
Nectocaris had a flattened, kite-shaped body with a fleshy fin running along the length of each side.[6] The small head had two stalked eyes, a single pair of tentacles, and a flexible funnel-shaped structure opening out to the underside of the body.[6] The funnel often gets wider away from the head.[6] The funnel has been suggested to represent an eversible (able to be turned inside out) pharynx.[3] Internally, a long cavity runs along the body axis, which is suggested to represent the digestive tract.[3] The body contains a pair of gills; the gills comprise blades emerging from a zig-zag axis. Muscle blocks surrounded the axial cavity, and are now preserved as dark blocks in the lateral body.[1] The fins also show dark blocks, with fine striations superimposed over them. These striations often stand in high relief above the rock surface itself.[1]
Diversity
Although Nectocaris is known from Canada, China and Australia, in rocks spanning some 20 million years, there does not seem to be much diversity; size excepted, all specimens are anatomically very similar. Historically, three genera have been erected for nectocaridid taxa from different localities, but these 'species' – Petalilium latus and Vetustovermis planus – likely belong to the same genus or even the same species as N. pteryx. Within N. pteryx, there seem to be two discrete morphs, one large (~10 cm in length), one small (~3 cm long). These perhaps represent separate male and female forms.[1]
Ecology
The unusual shape of the nectocaridid funnel has led to its interpretation as an eversible
Affinity
The affinity of Nectocaris is controversial.[7][3] Martin R Smith and Jean-Bernard Caron have suggested that nectocaridids represent early cephalopods. In a 2010 publication in Nature, they suggested that the ancestor of modern cephalopods and nectocaridids probably lacked a mineralised shell,[6] while Smith in a later 2013 publication suggested that it may be more plausible that nectocaridids had instead lost a mineralised shell and developed a morphology convergent on modern coleoids.[1] However, other authors contend that the morphology of nectocaridids is contrary to what is known about cephalopod and mollusc evolution, and they cannot be accommodated within these groups,[2][3][7] and can only be confidently placed as members of Bilateria.[3]
History of study
Nectocaris has a long and convoluted history of study. 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.[8]
Because the genus was originally known from a single, incomplete specimen and with no
Working from photographs, the Italian palaeontologist Alberto Simonetta believed he could classify Nectocaris within the chordates.[11] He focussed mainly on the tail and fin morphology, interpreting Conway Morris's 'gut' as a notochord – a distinctive chordate feature.[11]
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 only 2 tentacles instead of the 8 or 10 limbs of modern cephalopods. The structure previous researchers had identified as an oval carapace or shield behind the eyes[12] 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.[6]
Later independent analyses questioned the cephalopod interpretation, stating that it did not square with the established theory of
Vetustovermis
Vetustovermis (from Latin: "very old worm")
The original description of Vetustovermis hedged its bets regarding classification, but tentatively highlighted some similarities with the
Early press reports misspelled the genus name as Vetustodermis.
Petalilium
Petalilium (sometimes misspelled Petalium)
Fossils of Petalilium[a] show a dorsoventrally flattened body, usually 5 to 6 centimetres, but ranging from 1.5 to 10 cm. It has an ovate trunk region and a large muscular foot, and a head with stalked eyes and a pair of long tentacles. The trunk region possesses about 50 soft, flexible, transverse bars, lateral serialised structures of unknown function. The upper part of the body, interpreted as a mantle, is covered with a random array of spines on the back, while gills project underneath. A complete, tubular gut runs the length of the body.
Whilst it was originally described as a
Some of the characters observed in Chen et al.'s (2005) study[17] suggested that Petalilium may be related to Nectocaris.[6]
See also
- Cambrian explosion
- Paleobiota of the Burgess Shale
- Chengjiang biota
Footnotes
References
- ^ S2CID 85744624.
- ^ PMID 35421982.
- ^ S2CID 2767810.
- S2CID 201208912.
- S2CID 85744624.
- ^ S2CID 4421029.
- ^ .
- ^ a b c Conway Morris, S. (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.
- ISBN 978-0-09-174271-3.
- JSTOR 2413615.
- ^ .
- S2CID 10491968.
- .
- ^ .
- ^ a b Luo, H.-L.; Hu, S.-X.; Chen, L.-Z. (1999). Early Cambrian Chengjiang fauna from Kunming region, China. Kunming, China: Yunnan Science & Technology Press.
- ^ "Strange fossil defies grouping". BBC News.
- ^ PMID 16191609.
- .
- S2CID 129162009.
- ^ Chen, L.Z.; Luo, H.L.; Hu, S.X.; Yin, J.Y.; Jiang, Z.W.; Wu, Z.L.; Li, F.; Chen, A.L. (2002). Early Cambrian Chengjiang Fauna in Eastern Yunnan, China (in Chinese and English). Kunming: Yunnan Science and Technology Press. p. 199.
- .
Further reading
- "Nectocaris pteryx". Burgess Shale Fossil Gallery. Virtual Museum of Canada. 2011. Archived from the original on 2020-11-12. – 3D animations are available and a more detailed consideration of Nectocaris
- Switek, Brian (5 July 2011). "Nectocaris: What the heck is this thing?". Laelaps. – Brian Switek discusses the taxonomy and history of Nectocaris in his blog
- Moskvitch, Katia (27 May 2010). "Mystery fossil is ancestor of squid". BBC News. – BBC News coverage of the Smith & Caron's (2010) re-description
- Taylor, Christopher (14 January 2011). "So nice when people agree with you". Catalogue of Organisms. – a blog article supporting Mazurek & Zatoń's (2011) view
- 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