Anomotodon: a Cretaceous shark known from its teeth

Anomotodon is an extinct lamniform shark known chiefly from isolated teeth. Its type species, A. plicatus, was named from North African fossil material, and later records include teeth from European Cretaceous chalk. The crowns preserve useful information about tooth position and surface folds, but no associated skeleton establishes the full body outline. It is one of the tooth-based records in the ancient fish catalogue.

Quick facts

A shark genus diagnosed from a limited record

Camille Arambourg introduced Anomotodon in 1952 for fossil shark teeth from North African phosphate deposits. The type species is A. plicatus. Later work commonly places the genus among lamniform sharks and often in Mitsukurinidae, the family that includes the living goblin shark. That family-level placement is based on tooth morphology and comparative classification, not on a complete Anomotodon skeleton.

Shark teeth fossilise much more readily than cartilage. Their enamel-like crowns resist decay, and sharks replace teeth continuously. A deposit can therefore contain many teeth without preserving a single jaw. The material may represent different individuals, ages and tooth positions. This pattern is useful for documenting shark diversity, but it makes genus and species boundaries difficult to assess.

What a tooth can identify

Teeth assigned to Anomotodon are typically narrow and slender, with a main cusp and no distinct lateral cusplets. Fine folds or striations can occur near the base of the crown, especially on the tongue-facing surface of some anterior teeth. The root divides into lobes, and details of its outline help distinguish similar-looking lamniform teeth.

The tooth of A. plicatus from the Late Cretaceous chalk of Denmark illustrates the level of evidence available. Researchers described a single well-preserved lateral tooth from the Højerup Member at Stevns Klint. Its shape can be compared with the type species and other shark teeth in the same succession. It cannot, by itself, reveal the animal’s complete dental formula or total length.

Tooth shape changes along a shark’s jaw. Front teeth used for gripping, lateral teeth that cut or hold, and intermediate teeth may look different even in one individual. Wear can remove fine ornament, while growth can alter crown proportions. Reliable identification therefore uses several characters together and, where possible, compares teeth from associated rows.

Body and diet remain inferences

No complete skull, vertebral column or fin skeleton is securely known for Anomotodon. A long-bodied lamniform silhouette is a reasonable comparison, but the length of the snout, size of the fins and position of the gills are not direct observations. A reconstruction that borrows the broad outline of a living goblin shark should be labelled as comparative, not as a portrait confirmed by fossils.

The slender pointed crowns could have gripped small fish or soft-bodied marine animals. This is a functional inference from tooth shape. No stomach contents, prey remains in the mouth or unambiguous bite marks establish a specific diet. The fish and invertebrates found in the same formation describe a marine community, but co-occurrence alone does not prove a predator-prey link.

Body-size estimates based on an isolated tooth require a comparison with a shark whose tooth positions and body proportions are already known. Choose a different analogue, and the estimated length can change substantially. The teeth assigned to Anomotodon do not justify a precise total length, and no robust mass estimate is available.

Range and changing identifications

The type species is Late Cretaceous. Reports from other parts of Europe, North Africa and Asia extend the genus across multiple marine basins. Some isolated teeth have also been assigned to younger deposits, but a long time range needs stronger support than a superficial resemblance. Reworking can move an older tooth into younger sediment, and other shark genera may evolve similar crown shapes.

Studies of Cretaceous–Palaeogene shark communities use Anomotodon plicatus as one element in changing assemblages. The presence of the species in a particular bed can help describe local diversity; it does not establish that the genus survived unchanged into later epochs. Each tooth’s formation, horizon, preservation and diagnostic features should be assessed separately.

Anomotodon is a good example of both the power and the limit of tooth fossils. The crowns can identify a shark lineage and suggest how it captured food, while leaving the whole body and exact ecology beyond direct view. An illustration can show a cautious lamniform outline, but its scale, colour and behaviour remain artistic reconstruction.

Explore related evidence in the ancient fish catalogue.