Opabinia Fossil range: Middle Cambrian
Conservation status
Extinct (fossil)
Scientific classification
Kingdom: Animalia Phylum: Problematica Class: Dinocarida Order: Radiodonta Genus: Opabinia Species: O. regalis
Binomial name
Opabinia regalis Walcott

Opabinia is a fossil animal found in Cambrian fossil deposits. Its sole species, Opabinia regalis, is known from the Middle Cambrian Burgess Shale of British Columbia. Myoscolex, from the Lower Cambrian Emu Bay shale of South Australia, is a possible relative. The discoverer of Opabinia, Charles Doolittle Walcott, named it after a local mountain, Opabin Peak in the Canadian Rockies. It is known from fewer than twenty good specimens. The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... Image File history File linksMetadata No higher resolution available. ... The conservation status of a species is an indicator of the likelihood of that species continuing to survive either in the present day or the future. ... For other uses, see Fossil (disambiguation). ... Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. ... For other uses, see Animal (disambiguation). ... Problematica can be:- A pseudo-phylum used for animals or plants whose classification cannot be decided. ... A group of creatures regarded as the sister phylum to arthropods. ... This article does not cite any references or sources. ... Charles Doolittle Walcott (March 31, 1850 _ February 9, 1927) was an eminent American invertebrate paleontologist. ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... For other uses, see Fossil (disambiguation). ... Hallucigenia sparsa, one of the organisms unique to the Burgess Shale. ... Motto: Splendor Sine Occasu (Latin: Splendour Without Sunset (diminishment)) Capital Victoria Largest city Vancouver Official languages English Government - Lieutenant-Governor Iona Campagnolo - Premier Gordon Campbell (BC Liberal) Federal representation in Canadian Parliament - House seats 36 - Senate seats 6 Confederation July 20, 1871 (6th province) Area  Ranked 5th - Total 944,735... North Coast of Kangaroo Island, Emu Bay © David Simpson The Emu Bay shale formation is one of two major Konservat-Lagerstätten (fossil beds with soft tissue preservation) in the world containing fossilised Redlichiida, an order of trilobite. ... Capital Adelaide Government Constitutional monarchy Governor Marjorie Jackson-Nelson Premier Mike Rann (ALP) Federal representation  - House seats 11  - Senate seats 12 Gross State Product (2004-05)  - Product ($m)  $59,819 (5th)  - Product per capita  $38,838/person (7th) Population (End of September 2006)  - Population  1,558,200 (5th)  - Density  1. ... Charles Doolittle Walcott (March 31, 1850 - February 9, 1927) was an eminent American invertebrate paleontologist. ... Ringrose Peak, Lake OHara, British Columbia, Canada The Canadian Rockies comprise the Canadian segment of the North American Rocky Mountains range. ...

The animal was segmented and had an unmineralized exoskeleton. Total body length ranged from 40 to 70 millimeters. The head carried five stalked eyes that would have given their owner a range of vision of almost 360°, and a long, flexible, hose-like proboscis. At the end of the proboscis were grasping spines; these are theorised to have served as a grab to catch prey, which would then be brought to the mouth, which was located underneath the head, behind the base of the proboscis. In general, a proboscis (from Greek pro before and boskein to feed) is an elongated appendage from the head of an animal. ... This page is a candidate to be moved to Wiktionary. ...

The body segments each featured a set of gills and a pair of flap-like appendages that are also dissimilar to other known animals of the time, save Anomalocaris. The three rearmost flaps formed the tail. Unlike known arthropods, the head does not appear to be formed from fused segments. For other uses, see Gill (disambiguation). ... This article does not cite any references or sources. ... Subphyla and Classes Subphylum Trilobitomorpha Trilobita - trilobites (extinct) Subphylum Chelicerata Arachnida - spiders,scorpions, etc. ...

Opabinia is thought to have lived on top of the soft sediment on the seabed, although it presumably could have swum after prey using its side flaps. On the bottom, the proboscis could have plunged into burrows after worms. It could also have been used to rapidly stir up sea floor sediment in search of food. If this were the case, Opabinia would then have folded back the proboscis to bring the food to its mouth on the underside of its head.

History of classification

The unusual morphology of Opabinia led to several attempts at classification in the last 100 years. For example, Walcott, the original describer, considered it to be an anostracan crustacean, whilst Leif Størmer, following earlier work by Percy Raymond, thought that it belonged to the so-called "trilobitoids". However, modern studies of Opabinia were initiated by the comprehensive redescription by Harry Blackmore Whittington in 1975, who showed that the frontal structure was a flexible, probably fluid-filled nozzle. Whittington could find no evidence for arthropodan jointed limbs, despite dissecting through the body of the animal to where they would be expected to be found. Harry Blackmore Whittington (born March 24, 1916) is a noted British paleontologist. ...

The lack of limbs, the annulated but not articulated body, and the unusual lateral lobes with gills led Whittington to conclude that Opabinia was no arthropod. Although he left its classification above the family level open, he considered that it may have been a representative of the ancestral stock from which both the annelids and arthropods arose. The demonsration that Opabinia, and other taxa such as Marrella and Yohoia, cannot be accommodated in modern groups was one of the primary reasons that Stephen J. Gould in his book on the Burgess Shale Wonderful Life, considered that Cambrian life was much more diverse and "experimental" than the extant fauna. Binomial name Marrella splendens Walcott, 1912 Marrella splendens is an unusual arthropod known from fossils found in only a single stratum of the Middle Cambrian Burgess Shale of British Columbia. ... Yohoia is a tiny, extinct animal from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. ... Stephen Jay Gould Stephen Jay Gould (September 10, 1941 – May 20, 2002) was a New York-born American paleontologist, evolutionary biologist, and historian of science. ... Hallucigenia sparsa, one of the organisms unique to the Burgess Shale. ... Wonderful Life (1989) is a book on evolution by Stephen Jay Gould. ...

At the time that Whittington's redescription of Opabinia was published, the animal appeared unique. However, a decade later in 1985, Derek Briggs and Whittington published a description of Anomalocaris, also from the Burgess Shale. The Swedish palaeontologist Jan Bergström soon suggested that the two animals were related, based on their shared lateral flaps with gills, stalked eyes and other features. In 1996, Graham Budd suggested that Opabinia was in fact a lobopod, and that it fell within the stem group of the Euarthropoda, along with the anomalocaridids. The details of Budd's reconstruction have recently been criticised by Zhang and Briggs, although they retain Budd's original placement of Opabinia and Anomalocaris in the euarthopod stem group. The morphology of Opabinia thus remains controversial in several details. Derek Briggs is an Irish paleontologist based at Yale University, USA. Whilst at Cambridge University, he worked on the fossils of the Cambrian Burgess Shale of British Columbia, along with Harry Blackmore Whittington and Simon Conway Morris. ... This article does not cite any references or sources. ... Graham Edward Budd (born September 7, 1968, Colchester) is a British-Swedish palaeontologist, associate professor of paleobiology at Uppsala University. ... In palaeontology, a stem group is a systematic grouping that is required to accommodate fossils in the classification of organisms. ... Euarthropod, or formally the Euarthropoda is a term that is often used to refer to the well-sclerotised arthropod clades, i. ...

The resemblance of Opabinia to some of the so-called "great appendage" arthropods such as Yohoia has led some workers either to place these arthropods at the top of the euarthropod stem group, or to return Opabinia to the euarthropod crown group, in the stem group of the chelicerates. Thus, despite general agreement that Opabinia belongs within the total group of the arthropods, its exact placement remains disputed. Yohoia is a tiny, extinct animal from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. ... A crown group is a living monophyletic group or clade, consisting of the last common ancestor of all living examples, plus all of its descendants. ... Classes Arachnida Merostomata Pycnogonida †Eurypterida The Subphylum Chelicerata constitutes one of the major subdivisions of the Phylum Arthropoda, including the arachnids, horseshoe crabs, and related forms. ...

See also

• Body plan

This article or section is in need of attention from an expert on the subject. ...

References

• Bergström, J. (1986). Opabinia and Anomalocaris, unique Cambrian arthropods. Lethaia 19, 241-246.
• Bergström, J. (1987). The Cambrian Opabinia and Anomalocaris. Lethaia 20, 187-188.
• Briggs, D. E. G. & Whittington, H. B. (1987). The affinities of the Cambrian animals Anomalocaris and Opabinia. Lethaia 20, 185-186.
• Budd, G. E. (1996). The morphology of Opabinia regalis and the reconstruction of the arthropod stem-group. Lethaia 29, 1-14.
• Whittington, H. B. (1975). The enigmatic animal Opabinia regalis, Middle Cambrian Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London B 271, 1-43.
• Zhang, X. & Briggs, D. E. G. (2007). The nature and significance of the appendages of Opabinia from the Middle Cambrian Burgess Shale. Lethaia 40, 161-173.

Further reading

• Stephen Jay Gould, Wonderful Life: The Burgess Shale and the Nature of History. (Norton: 1989)
• Xian-Guang Hou, The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life. (Blackwell, 2004)

External links

• Smithsonian page on Opabinia, with photo of Burgess Shale fossil