Dinomischus

Dinomischus is a rare fossil animal from the Cambrian period. It reached 20 mm in height,[1] was attached to the sea floor by a stalk, and looked loosely like a flower. The cup-shaped body at the top of the stalk probably fed by filtering the surrounding seawater, and may have created a current to facilitate this.[2] Its mouth and anus sat next to one another.

Dinomischus
Temporal range: Chengjiang–Burgess Shale
Reconstruction of two Dinomischus in their environment.
Scientific classification
Kingdom:
Animalia
Genus:
Dinomischus
Type species
Dinomischus isolatus
Species
  • D. isolatus
  • D. venustus

In his pioneering excavations of the Burgess Shale, Charles Doolittle Walcott excavated the first, and at the time only, specimen. It had evidently caught his eye, for he had taken the trouble to carefully photograph it—but he never found the time to describe the organism, and it was not until 1977 that Simon Conway Morris described the animal. He tracked down two further specimens, collected by further expeditions by teams from Harvard and the Royal Ontario Museum, allowing him to produce a reconstruction.[3]

He was not able to say much about the organism. It consisted of a calyx (or body) on a long, thin stalk, surrounded by a whorl of 18 short "petals", which enclosed both openings of its U-shaped gut.[1] The presence of this gut identified it as a metazoan, and the stem implied that it lived permanently attached to the sea floor by a small holdfast.[3] The twenty or so "petals" borne by each organism were solid, plate-like structures, about two thirds the length of the calyx. It is speculated that they may have been covered with cilia—fine hairs—which would have wafted food down towards the organism's mouth.[3] A number of affinities were considered, but on the basis of available evidence it didn't quite seem to fit into any extant phylum.[3] The most similar organisms were the much smaller entoprocts, but even these modern organisms are difficult to classify.[4]

Further specimens have since been produced by similarly spectacular fossil sites in China. 13 have been found in the Chengjiang, then in 2006 one specimen was identified within the Kaili Formation.[5] These organisms merited the erection of a new species, D. venustus, as their corrugated "petals" possessed radial rays.[6] However, these new data have added little to the debate; while a suggestion of echinoderm affinity has been floated,[7] no phyla are compellingly similar to the organism.[8] Other modern ideas, even if a little tenuous, include a suggestion that the organism may have been parasitic, dwelling on the carapaces of larger organisms.[9] 13 specimens of Dinomischus are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.[10]

Dinomischus is not the only sessile, stalked organism from the Cambrian, but it has no obvious relatives in other genera. Siphusauctum gregarium (known as the "tulip animal") has been recovered from the Burgess Shale, but has a clearly different basic anatomy, with multiple openings at the base of the calyx, an anus at the top, and a large six-petaled internal organ interpreted as a filter-feeding device.[11] Dinomischus has also been likened to Eldonia and Velumbrella, although unlike Dinomischus these medusoid organisms have tentacles.[12]

References
  1. Hou, X.-G. (2004). The Cambrian Fossils of Chengjiang, China : The Flowering of Early Animal Life. Blackwell Publishing. ISBN 978-1-4051-0673-3.
  2. "Dinomischus isolatus". Hooper Virtual Paleontological Museum.
  3. Morris, S.C. (1977). "A new entoproct-like organism from the Burgess Shale of British Columbia" (PDF). Palaeontology. 20 (4): 833–845.
  4. Lieberman, B.S. (2008). "The Cambrian radiation of bilaterians: Evolutionary origins and palaeontological emergence; earth history change and biotic factors". Palaeogeography, Palaeoclimatology, Palaeoecology. 258 (3): 180–188. doi:10.1016/j.palaeo.2007.05.021.
  5. Peng, J.; Zhao, Y.; Lin, J.-P. (2006). "Dinomischus from the Middle Cambrian Kaili Biota, Guizhou, China". Acta Geologica Sinica. 80 (4): 498–501.
  6. Hagadorn, J.W. (2002). "Chengjiang: Early Record of the Cambrian Explosion". In Bottjer, D.J.; Etter, W.; Hagadorn, J.W.; Tang, C.M. (eds.). Exceptional Fossil Preservation: a unique view on the evolution of marine life. Columbia University Press. ISBN 978-0-231-10255-1.
  7. Chen, J.Y.; Zhou, G.Q. (1997). "Biology of the Chengjiang fauna". Bull. Natl. Mus. Nat. Sci. 10: 11–105.
  8. Morris, S.C. (1987). "Cambrian enigmas". Geology Today. 3 (3–4): 88–92. doi:10.1111/j.1365-2451.1987.tb00495.x.
  9. Bassett, M.G.; Popov, L.E.; Holmer, L.E. (2004). "The Oldest-Known Metazoan Parasite?" (PDF). Journal of Paleontology. 78 (6): 1214–1216. doi:10.1666/0022-3360(2004)078<1214:TOMP>2.0.CO;2. ISSN 0022-3360.
  10. Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. doi:10.2110/palo.2003.P05-070R. JSTOR 20173022.
  11. O'Brien, Lorna J.; Caron, Jean-Bernard (2012-01-18). "A New Stalked Filter-Feeder from the Middle Cambrian Burgess Shale, British Columbia, Canada". PLoS ONE. 7 (1): e29233. doi:10.1371/journal.pone.0029233. ISSN 1932-6203. PMC 3261148. PMID 22279532.
  12. Dzik, J. (1991). "Is fossil evidence consistent with traditional views of the early metazoan phylogeny?" (PDF): 47–56. Cite journal requires |journal= (help)

Further reading
  • Briggs, Erwin & Coller (1995). Fossils of the Burgess Shale. Smithsonian Institution Press. ISBN 978-1-56098-659-1. OCLC 231793738.
  • Hou, X.-G. (2004). The Cambrian Fossils of Chengjiang, China : The Flowering of Early Animal Life. Blackwell Publishing. ISBN 978-1-4051-0673-3.
  • Knoll, A.H. (1996). "Daughter of time". Paleobiology.
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