Plicatoscyllium: a carpet shark known from tiny teeth

Plicatoscyllium is an extinct carpet-shark genus recognised chiefly from very small teeth in Late Cretaceous marine deposits. The tooth crowns can carry conspicuous folds on the labial face and distinct lateral cusplets, but no complete skeleton fixes the animal’s proportions. Teeth associated with the Maastrichtian mosasaur Prognathodon saturator have also been discussed alongside bite marks and a scattered skeleton as evidence of shark scavenging. The genus belongs in the ancient fish catalogue as a case where ecological clues and taxonomic evidence remain separate.

Quick facts

A genus erected from teeth

G. R. Case and Henri Cappetta introduced Plicatoscyllium in 1997 while describing a selachian fauna from the Late Maastrichtian Kemp Formation of Texas. The genus gathered species that had previously been placed among living nurse sharks, showing that older names were being applied to fossils with a different combination of dental features. Subsequent studies have reported related teeth in several Late Cretaceous regions, but each species assignment still depends on the characters preserved in its own material.

Shark cartilage is less likely to fossilise than enamel-like tooth crowns, and sharks replace teeth continually. A bed can therefore yield many isolated teeth without a jaw or skeleton. In Plicatoscyllium, that record is particularly small and tooth-centred. A specimen can establish that a shark of this kind was present, but it cannot by itself show the total length, fin shape, skin pattern or behaviour of the animal.

Reading the folded crown

Teeth assigned to the genus tend to have a relatively low crown with a central cusp and one or more lateral cusplets. Fine vertical folds mark the labial, or outward-facing, surface of the crown. Their number, strength and distribution vary among species and across tooth positions. The root may have separated lobes and a broad lingual projection, features that help distinguish specimens from superficially similar carpet-shark teeth.

Small size alone is not a diagnosis. Fossil teeth can be juvenile, worn, broken or positioned toward the side of the jaw. A lateral tooth may have a broader crown or differently developed cusplets than an anterior one in the same mouth. Researchers compare the crown base, folds, cusplets and root together, and keep uncertain fragments at an open taxonomic level rather than forcing a species name.

What the mosasaur association suggests

The Maastrichtian mosasaur Prognathodon saturator from the Netherlands preserves bite marks and a partially disarticulated, scattered skeleton. Teeth attributed to the sharks Squalicorax and Plicatoscyllium were found in association with it. The authors interpreted the combination as evidence of extensive shark scavenging. The bite marks and shed teeth support that event in this particular setting, although the teeth alone do not identify which shark made every mark.

This is a useful ecological clue because ordinary isolated teeth rarely preserve a feeding interaction. It does not establish that Plicatoscyllium routinely attacked large reptiles, or that all individuals were scavengers. A carcass can attract several sharks, and the association records a specific episode after death. It cannot define the whole diet or behaviour of a genus whose other fossils are mostly separate teeth.

Distribution and classification

Late Cretaceous teeth referred to Plicatoscyllium have been reported from western Europe, North Africa, the Middle East and North America. The range spans multiple marine basins, but it is assembled from species-level identifications that have been revised over time. Some younger reports are tentative and should not extend the genus range without a clear comparison to the diagnostic tooth pattern.

The genus is generally treated among orectolobiform sharks, the broad group that includes modern carpet sharks. Family placement has often been given as Ginglymostomatidae, but the evidence is dental and the membership of fossil species has changed. It is more accurate to describe Plicatoscyllium as an extinct carpet-shark lineage than to assert that a complete modern nurse-shark body plan is known.

Limits of the reconstruction

A modest, bottom-associated shark outline is a reasonable illustration based on the broad group, but it is comparative. The fossils do not preserve original colour, the exact position of fins, body length or daily behaviour. A reconstruction should show that uncertainty rather than imply that the tiny teeth document a complete animal.

For comparison, the broad crushing plates of Pycnodus preserve a different feeding system in articulated fish fossils. Plicatoscyllium remains a tooth-based shark record: useful for identifying a lineage and a rare scavenging association, but limited for the shape and life history of the animal itself.

Explore related evidence in the ancient fish catalogue.