Nectocaris

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Nectocaris
Temporal range: Cambrian Stage 3–Wuliuan
Nectocaris pteryx (ROM 60079).jpg
Specimen ROM 60079
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Family:† Nectocarididae
Genus:† Nectocaris
Conway Morris, 1976
Species:
†N. pteryx
Binomial name
†Nectocaris pteryx

Nectocaris is a genus of squid-like animal of controversial affinities known from the Cambrian period. The initial fossils were described from the Burgess Shale of Canada. Other similar remains possibly referrable to the genus are known from the Emu Bay Shale of Australia and Chengjiang Biota of China.

Contents

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 59660.jpg
Nectocaris pteryx from the Burgess Shale; funnel is visible folded to left of specimen. Image from Smith (2013). [5]

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

Life restoration Nectocaris pteryx.jpg
Life restoration

The unusual shape of the nectocaridid funnel has led to its interpretation as an eversible proboscis. Martin R Smith and Jean-Bernard Caron have suggested that it was used for jet propulsion, [6] [1] though this has been questioned by other authors. [7] The eyes of Nectocaris would have had a similar visual acuity to modern Nautilus (if they lacked a lens) or squid (if they did not). [1] They are thought to have been freely-swimming nektonic organisms, [3] that were either scavengers or predators on soft-bodied animals, using their tentacles to manipulate food items. [6]

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

Original (and obsolete) 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. Nectocaris.jpg
Original (and obsolete) 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.

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 counterpart, [9] Conway Morris was unable to deduce its affinity. It had some features which were reminiscent of arthropods, but these could well have been convergently derived. [8] [10] Its fins were very unlike those of arthropods. [8]

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 cephalopod evolution, and that nectocaridids should be considered incertae sedis among Bilateria. [13] [7] [3] [2]

Vetustovermis

Vetustovermis (from Latin: "very old worm") [14] is a soft-bodied middle Cambrian animal, known from a single reported fossil specimen from the South Australian Emu Bay shale. It is probably a junior synonym of Nectocaris pteryx. [1]

The original description of Vetustovermis hedged its bets regarding classification, but tentatively highlighted some similarities with the annelid worms. [14] It was later considered an arthropod, [15] [16] and in 2010 Smith and Caron, agreeing that Petalilium was at least a close relative of Vetustovermis (but that treating it as a synonym was premature, given the poor preservation of the Vetustovermis type), placed it with Nectocaris in the clade Nectocarididae. [6]

Early press reports misspelled the genus name as Vetustodermis.

Petalilium

Petalilium (sometimes misspelled Petalium) [17] is an enigmatic genus of Cambrian organism known from the Haikou area, [18] from the Maotianshan mudstone member of the Chengjiang biota. [19] The taxon is a junior synonym of Nectocaris pteryx. [1]

Fossils of Petalilium [lower-alpha 1] 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 phyllocarid, [15] and a ctenophore affinity has been suggested, [20] neither interpretation is supported by any compelling evidence. [21]

Some of the characters observed in Chen et al.'s (2005) study [17] suggested that Petalilium may be related to Nectocaris. [6]

See also

Footnotes

  1. ↑ Petalilium was originally described as Vetustovermis by Chen et al. (2005), [17] but recognised as Petalilium by Smith & Caron (2010). [6]

Related Research Articles

<span class="mw-page-title-main">Burgess Shale</span> Fossil-bearing rock formation in the Canadian Rockies

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 508 million years old, it is one of the earliest fossil beds containing soft-part imprints.

<i>Hallucigenia</i> Genus of Cambrian animals

Hallucigenia is a genus of lobopodian, known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.

<span class="mw-page-title-main">Maotianshan Shales</span> Series of Early Cambrian deposits in the Chiungchussu Formation

The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation, famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill in Chengjiang County, Yunnan Province, China.

<i>Amiskwia</i> Genus of extinct, gnathiferan worms

Amiskwia is a genus of soft-bodied animals known from fossils of the Middle Cambrian Lagerstätten both in the Burgess Shale in British Columbia, Canada and the Maotianshan shales of Yunnan Province, China. It is interpreted as a member of the clade Gnathifera sensu lato.

<span class="mw-page-title-main">Coleoidea</span> Subclass of cephalopods

Coleoidea or Dibranchiata, is one of the two subclasses of cephalopods, containing all the various taxa popularly thought of as "soft-bodied" or "shell-less". Unlike its extant sister group Nautiloidea, whose members have a rigid outer shell for protection, the coleoids have at most an internal shell called cuttlebone or gladius that is used for buoyancy or as muscle anchorage. Some species, notably incirrate octopuses, have lost their cuttlebone altogether, while in some it has been replaced by a chitinous support structure. A unique trait of the group is the ability to edit their own RNA.

<i>Pikaia</i> Extinct genus of primitive chordates

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<i>Wiwaxia</i> Genus of Cambrian animals

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 Cambrian and middle Cambrian fossil deposits across the globe. The living animal would have measured up to 5 cm (2 inch) when fully grown, although a range of juvenile specimens are known, the smallest being 2 millimetres (0.079 in) long.

<i>Anomalocaris</i> Extinct genus of anomalocaridid (also extinct)

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<i>Waptia</i> Cambrian arthropod

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<i>Dinomischus</i>

Dinomischusis an extinct genus of stalked filter-feeding animals with the Cambrian period, with specimens known from the Burgess Shale and the Maotianshan Shales. While long of uncertain affintiies, recent studies have suggested it to be a stem-group ctenophore.

A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale. While many are also preserved in a similar fashion to the Burgess Shale, the term "Burgess Shale-type fauna" covers assemblages based on taxonomic criteria only.

The fossils of the Burgess Shale, like the Burgess Shale itself, are fossils that formed around 505 million years ago in the mid-Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 65,000 specimens in a series of field trips up to the alpine site from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection continue to reveal new species, and statistical analysis suggests that additional discoveries will continue for the foreseeable future. Stephen Jay Gould's 1989 book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.

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<i>Herpetogaster</i> Extinct genus of Cambrian animals

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The Cambrian chordates are an extinct group of animals belonging to the phylum Chordata that lived during the Cambrian, between 485 and 538 million years ago. The first Cambrian chordate known is Pikaia gracilens, a lancelet-like animal from the Burgess Shale in British Columbia, Canada. The discoverer, Charles Doolittle Walcott, described it as a kind of worm (annelid) in 1911, but it was later identified as a chordate. Subsequent discoveries of other Cambrian fossils from the Burgess Shale in 1991, and from the Chengjiang biota of China in 1991, which were later found to be of chordates, several Cambrian chordates are known, with some fossils considered as putative chordates.

References

  1. 1 2 3 4 5 6 7 8 9 Smith, M.R. (2013). "Nectocaridid ecology, diversity and affinity: Early origin of a cephalopod-like body plan". Paleobiology. 39 (2): 291–321. Bibcode:2013Pbio...39..297S. doi:10.1666/12029. S2CID   85744624.
  2. 1 2 3 Pohle, Alexander; Kröger, Björn; Warnock, Rachel C. M.; King, Andy H.; Evans, David H.; Aubrechtová, Martina; Cichowolski, Marcela; Fang, Xiang; Klug, Christian (December 2022). "Early cephalopod evolution clarified through Bayesian phylogenetic inference". BMC Biology. 20 (1): 88. doi: 10.1186/s12915-022-01284-5 . ISSN   1741-7007. PMC   9008929 . PMID   35421982.
  3. 1 2 3 4 5 6 7 8 9 Kröger, Björn; Vinther, Jakob; Fuchs, Dirk (August 2011). "Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules". BioEssays. 33 (8): 602–613. doi:10.1002/bies.201100001. PMID   21681989. S2CID   2767810.
  4. ↑ Smith, Martin R. (2019). "An Ordovician nectocaridid hints at an endocochleate origin of Cephalopoda" (PDF). Journal of Paleontology. 94: 64–69. doi:10.1017/jpa.2019.57. S2CID   201208912.
  5. ↑ Smith, Martin R. (2013). "Nectocaridid ecology, diversity, and affinity: Early origin of a cephalopod-like body plan". Paleobiology. 39 (2): 297–321. Bibcode:2013Pbio...39..297S. doi:10.1666/12029. S2CID   85744624.
  6. 1 2 3 4 5 6 7 8 9 10 Smith, M.R.; Caron, J.B. (2010). "Primitive soft-bodied cephalopods from the Cambrian". Nature. 465 (7297): 469–472. Bibcode:2010Natur.465..469S. doi:10.1038/nature09068. hdl: 1807/32368 . PMID   20505727. S2CID   4421029.
  7. 1 2 3 4 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.
  8. 1 2 3 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.
  9. ↑ Gould, S.J. (1989). Wonderful Life: The Burgess Shale and the Nature of History. Hutchison Radius. Bibcode:1989wlbs.book.....G. ISBN   978-0-09-174271-3.
  10. ↑ 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.
  11. 1 2 Simonetta, A.M. (1988). "Is Nectocaris pteryx a chordate?". Bollettino di Zoologia. 55 (1–2): 63–68. doi: 10.1080/11250008809386601 .
  12. ↑ Conway Morris, Simon (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. S2CID   10491968.
  13. ↑ Mazurek, D.; Zatoń, M. (2011). "Is Nectocaris pteryx a cephalopod?". Lethaia. 44: 2–4. doi:10.1111/j.1502-3931.2010.00253.x.
  14. 1 2 Glaessner, M.F. (1979). "Lower Cambrian Crustacea and annelid worms from Kangaroo Island, South Australia". Alcheringa: An Australasian Journal of Palaeontology. 3 (1): 21–29. Bibcode:1979Alch....3...21G. doi:10.1080/03115517908565437.
  15. 1 2 Luo, H.-L.; Hu, S.-X.; Chen, L.-Z. (1999). Early Cambrian Chengjiang fauna from Kunming region, China. Kunming, China: Yunnan Science & Technology Press.
  16. ↑ "Strange fossil defies grouping". BBC News.
  17. 1 2 3 Chen, J.Y.; Huang, D.Y.; Bottjer, D.J. (2005). "An Early Cambrian problematic fossil: Vetustovermis and its possible affinities". Proceedings of the Royal Society B. 272 (1576): 2003–2007. doi:10.1098/rspb.2005.3159. PMC   1559895 . PMID   16191609.
  18. ↑ Steiner, M.; Zhu, M.; Zhao, Y.; Erdtmann, B. (2005). "Lower Cambrian Burgess Shale-type fossil associations of South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 220 (1–2): 129–152. Bibcode:2005PPP...220..129S. doi:10.1016/j.palaeo.2003.06.001.
  19. ↑ Han, J.; Shu, D.; Zhang, Z.; Liu, J.; Zhang, X.; Yao, Y. (2006). "Preliminary notes on soft-bodied fossil concentrations from the Early Cambrian Chengjiang deposits". Chinese Science Bulletin. 51 (20): 2482. Bibcode:2006ChSBu..51.2482H. doi:10.1007/s11434-005-2151-0. S2CID   129162009.
  20. ↑ 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.
  21. ↑ Hu, S.; Steiner, M.; Zhu, M.; Erdtmann, B.D.; Luo, H.; Chen, L.; Weber, B. (2007). "Diverse pelagic predators from the Chengjiang Lagerstätte and the establishment of modern-style pelagic ecosystems in the early Cambrian". Palaeogeography, Palaeoclimatology, Palaeoecology. 254 (1–2): 307–316. Bibcode:2007PPP...254..307H. doi:10.1016/j.palaeo.2007.03.044.

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