Odontogriphus (from Greek: ὀδούς odoús, 'tooth' and Greek: γρῖφος grîphos, 'riddle') is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as 12.5 centimetres (4.9 in) in length, Odontogriphus is a flat, oval bilaterian which apparently had a single muscular foot and a "shell" on its back that was moderately rigid but of a material unsuited to fossilization.
Originally it was known from only one specimen, but 189 new finds in the years immediately preceding 2006 made a detailed description possible. (221 specimens of Odontogriphus are known from the Greater Phyllopod bed, where they comprise 0.42% of the community.[3]) As a result, Odontogriphus has become prominent in the debate that has gone on since 1990 about the evolutionary origins of molluscs, annelid worms and brachiopods. It is thought that Odontogriphus's feeding apparatus, which is "nearly identical" to Wiwaxia's, is an early version of the molluscan radula, a chitinous "tongue" that bears multiple rows of rasping teeth. Hence Odontogriphus and Wiwaxia are often classified as closely related to true molluscs.
Charles Doolittle Walcott found one specimen during one of his field trips to the Burgess Shale between 1910 and 1917. In the 1970s Simon Conway Morris re-examined the specimen and tentatively concluded that it was a swimming lophophorate, in other words related to the ancestors of molluscs, annelid worms and brachiopods.[1] In 2006 Caron, Scheltema et al. published a new analysis based on 189 recently collected specimens, all from the Burgess Shale.[4]
Odontogriphus was apparently a very rare species, accounting for less than 0.5% of the individual organisms found in the same fossil beds. Most of the fossils consist of two parts of a split block of rock, the upper part giving a "casting" of the animal's upper surface and the lower giving one of its underside.[4]
Odontogriphus was a flat-bodied animal ranging from 3.3 millimetres (0.13 in) to 125 millimetres (4.9 in) in length, with parallel sides and semi-circular ends. The specimens examined by Caron, Scheltema et al. (2006) had the same ratio of length to width irrespective of size. The body outlines are bilaterally symmetrical in all fairly complete specimens, even those in which internal features were preserved asymmetrically. Caron, Scheltema et al. (2006) interpreted this as evidence that the animals had on their backs "shells" that were rigid enough to resist whatever stresses distorted the internal features, but were not tough enough to be preserved by fossilization – similar, for example, to finger nails. Relatively broad wrinkles, parallel to each other and usually straight, run across the central region of the body in some specimens.[4]
Caron, Scheltema et al. (2006) found evidence of a circular mouth on the underside, with two and occasionally three tooth-bearing structures that they interpreted as a feeding apparatus and very similar to that of Wiwaxia. Odontogriphus's feeding apparatus was located on the midline, about 15% of the total body length from the front edge of the fossils.[4]The mouthparts comprised two to three rows, each comprising about two dozen carbonaceous teeth arranged symmetrically about a medial tooth, with one or two lateral teeth substantially smaller than the central teeth. The teeth operated by passing around an underlying "tongue", with the tooth rows deforming as they did so. The teeth probably scooped through the sea-floor mud, feeding on any detritus within it.[5]
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