Odontogriphus omalus

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A slug-like creature that scraped food from the ocean floor with its toothed tongue

3D animation of Odontogriphus omalus.

ANIMATION BY PHLESCH BUBBLE © ROYAL ONTARIO MUSEUM

Odontogriphus omalus (ROM 57712). The largest known specimen of the species (front to the top) on top of large sheets of the cyanobacterium Morania confluens. Specimen length = 125 mm. Specimen dry – polarized light (left), wet – polarized light (right). Walcott Quarry.

Odontogriphus omalus (ROM 57718). Complete specimen showing the radula (top) and an ingested tooth row, presumably shed, at the posterior end of the body. Specimen length = 58 mm. Specimen dry – direct light (left and right), wet – polarized light (middle). Walcott Quarry.

Odontogriphus omalus (ROM 57720) – Part and counterpart. Complete specimen showing the radula (top) and gills along the foot, particularly on the part. Specimen length = 110 mm. Specimen dry – polarized light (far left and middle right), wet – polarized light (middle left and far right). Walcott Quarry.

Odontogriphus omalus (ROM 57721). Complete specimen showing gills, gut trace and gut contents. Specimen length = 78 mm. Specimen dry – direct light (left), dry – polarized light (middle), wet – direct light (right). Walcott Quarry.

Odontogriphus omalus (ROM 57723) – Part and counterpart. Complete specimen compressed along its length and showing wrinkles in the area of the foot, particularly visible on the part. Specimen length = 70 mm. Specimen dry – polarized light (far left and middle right), wet – polarized light (middle left and far right). Walcott Quarry.

Odontogriphus omalus (USNM 196169) – Holotype, part and counterpart. Partial specimen showing the radula (top). Specimen length = 46 mm. Specimen dry – polarized light (left images), wet – polarized light (right images). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Mollusca

Higher Taxonomic assignment: Unranked clade halwaxiids (stem group molluscs)

Species name: Odontogriphus omalus

Remarks:

Odontogriphus is an early stem-group mollusc (Caron et al., 2006; Sigwart and Sutton, 2007), or a stem-group to the lophotrochozoans, a group which includes molluscs, annelids, and brachiopods (Conway Morris and Caron, 2007). A relationship to annelids (Butterfield, 2006) has been suggested, but appears less likely (Caron et al., 2007).

Described by: Conway Morris

Description date: 1976

Etymology:

Odontogriphus – from the Greek odontos, “tooth,” and griphos, “puzzle, or riddle,” in reference to its uncertain affinities.

omalus – from the Greek homalos, “flat,” in reference to the animal’s flattened shape.

Type Specimens: Holotype –USNM196169 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: none.

Age & Localities:

Age:

Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

Principal localities:

The Walcott Quarry on Fossil Ridge and the Tulip Beds (S7) on Mount Stephen.

History of Research:

Brief history of research:

Walcott collected the first specimen between 1909 and 1924 but it remained unstudied for more than half a century. Conway Morris “rediscovered” the part and counterpart of this specimen in different sections of the Walcott collection and described it in 1976 as Odontogriphus omalus. The affinities of Odontogriphus remained uncertain until the Royal Ontario Museum discovered 189 new specimens between 1990 and 2000, allowing for a thorough redescription of the animal (Caron et al., 2006).

Description:

Morphology:

This entirely soft-bodied animal is ovoid and dorsoventrally compressed, reaching up to 125 mm in length and 43 mm in width. The front and back are semicircular in outline and of similar size. The mouth is ventral with a radula composed of two primary tooth rows. A muscular foot extends from behind the mouth to the posterior part of the animal and is surrounded by gills (or ctenidia), except at the front. The dorsal surface is smooth and does not bear any shells, spines or plates. Internally, a large stomach is preserved with a narrow and straight intestine ending in a sub-terminal anus.

Abundance:

Most specimens come from the Walcott Quarry, where Odontogriphus represents 0.42% of the community (Caron and Jackson, 2008). A single specimen comes from Mount Stephen (S7 locality).

Maximum Size:

125 mm

Ecology:

Life habits: Epibenthic, Mobile

Feeding strategies: Herbivorous

Ecological Interpretations:

The presence of a radula suggests that Odontogriphus was a grazer, using its teeth to rasp and ingest food. Locomotory waves within the large foot would have enabled the animal to crawl along the surface of the mud. Odontogriphus might have fed on benthic, sheet-like masses of the cyanobacterium Morania, since fossils of both are often found associated in the same layers.

References:

BUTTERFIELD, N. J. 2006. Hooking some stem-group “worms”: fossil lophotrochozoans in the Burgess Shale. BioEssays, 28: 1161-1166.

CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER AND D. RUDKIN. 2006. A soft-bodied mollusc with radula from the Middle Cambrian Burgess Shale. Nature, 442: 159-163.

CARON, J.-B., A. H. SCHELTEMA, C. SCHANDER AND D. RUDKIN. 2007. Reply to Butterfield on stem-group “worms:” fossil lophotrochozoans in the Burgess Shale. BioEssays, 29: 200-202.

CONWAY MORRIS, S. 1976. A new Cambrian lophophorate from the Burgess Shale of British Columbia. Palaeontology, 19: 199-222.

SIGWART, J. D. AND M. D. SUTTON. 2007. Deep molluscan phylogeny: synthesis of palaeontological and neontological data. Proceedings of the Royal Society B: Biological Sciences, 274: 2413-2419.