Odontogriphus
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| Odontogriphus Fossil range: Middle Cambrian |
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 Artist's impression of Odontogriphus
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Odontogriphus (literally "toothed riddle") is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as 12 centimetres in length, Odontogriphus is a dorsoventrally flattened bilaterian, oval in shape, with a ventral U-shaped mouth surrounded by small protrusions.
Initially collected by Charles Doolittle Walcott, Odontogriphus was rediscovered and named by Simon Conway-Morris in the re-evaluation of the Burgess Shale fossils in the 1970s. Represented by only a single specimen, Conway-Morris proposed the protrusions around the mouth were probably lophophores, and reconstructed the animal as a free-swimming creature either in or related to the Lophophorata. It is easy to understand his reasoning in believing it was free-swimming, merely because of the scarcity of specimens of this particular fossil. Nearly all the Burgess genera represented by single specimens are clearly active swimmers, with fins and/or paddles.
Dzik (1995) later speculated that it may be an early chordate.
Caron et al. (2006) reported upon another 189 specimens of the same species, O. omalus, some of which had been exceptionally well preserved. The new specimens show tentative evidence of gill-like structures, arranged around the "foot", and evidence of a radula, a structure made up of rows of small tooth-like protrusions. This is a characteristic feature of molluscs and suggests that Odontogriphus belongs to this phylum. This would make 510 million year old Odontogriphus the second oldest known soft-bodied mollusc, after Kimberella.
Caron's team believed that O. omalus crawled over bacterial mats, scraping food into its mouth with its radula, rather than swimming freely, although it is possible it could swim if necessary, to escape predation or find new bacterial mats.
The newly studied specimens of Odontogriphus have caused speculation that Odontogriphus and another Burgess "proto-mollusc", Wiwaxia, may be closely related, having similar radula structures, and that they both may be descended from even older organisms, such as Kimberella. This would indicate that the phylum Mollusca may have roots as far back as the late Precambrian.
Four months later, Butterfield (2006) had published a response to Caron's assertions, suggesting that a thorough and detailed analysis of the structures identified as radulæ did not uphold such an interpretation, and that Odontogriphus is in fact a jawed segmented worm - though still belonging to the superphylum Lophotrochozoa.
This debate is ongoing (e.g. Caron et al. 2007; Butterfield 2007), and it seems that despite the increase in our knowledge of the creature, it will remain a "toothed riddle" for the foreseeable future.
[edit] External links
- Royal Ontario Museum article on O. omalus
- http://www.cbc.ca/health/story/2006/07/12/mollusc-fossil.html
[edit] References
- Bengtson, S. (2006-07-13). "A ghost with a bite". Nature(London) 442 (7099): 146–147. doi:.
- Butterfield, N.J. (2006). "Hooking some stem-group ‘‘worms’’: fossil lophotrochozoans in the Burgess Shale". Bioessays 28 (12): 1161–6. doi:.
- Butterfield, N.J. (2007). "Lophotrochozoan roots and stems" in Palaeontological Association Annual Meeting. Budd, G.E.; Streng, M.; Daley, A.C.; Willman, S. Programme with Abstracts 51: 26.
- Caron, J-B.; Scheltema, A.; Schander, C.; Rudkin, D. (2006-07-13). "A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale". Nature 442 (7099): 159–163. doi:.
- Caron, J-B. (2007-02-01). "Reply to Butterfield on stem-group "worms": fossil lophotrochozoans in the Burgess Shale". Bioessays 29 (2): 200–202. doi:. ISSN 0265-9247.
- Dzik, J. (1995). "Yunnanozoon and the ancestry of chordates" ([dead link]). Acta Palaeont Polonica 40: 341–360.
