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Odontogriphus (literally "toothed riddle") is a genus of relatively large animals from the middle Cambrian fossil deposits of the Burgess Shale in British Columbia. Growing as large as 12 centimetres long, 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 reasonable to assume part of his reasoning in believing it was free-swimming is the scarcity of specimens. Nearly all the Burgess genera represented by single specimens are clearly active swimmers, with fins and/or paddles. In July 2006, Nature reported that another 189 specimens of the same species, O. omalus, had been discovered, and some had been exceptionally well preserved. The new specimens show 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 points to Odontogriphus belonging to this phylum. Moreover, at around 510 million years old Odontogriphus is currently the second oldest known soft-bodied mollusc, after Kimberella. It is now believed that O. omalus crawled over bacterial mats, scraping food into its mouth with its radula, rather than swimmimg freely, although it is possible it could swim if necessary, to escape predation or find pastures new. The newly studied specimens of Odontogriphus, rooting as they do the molluscan line back so far with fair certainty, 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 indicates that the phylum Mollusca may have roots as far back as the late Precambrian.
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