Pachyscyllium gilberti

Pachyscyllium gilberti

Casier, 1946

Common Name: Catsharks

Fossil Group: Sharks & Rays
Order: Carcharhiniformes
Family: Scyliorhinidae
Genus: Pachyscyllium

Summary

Pachyscyllium gilberti, historically known as Premontreia gilberti, was a small extinct catshark known from Palaeocene and Eocene marine deposits. It is represented principally by tiny teeth that are generally only a few millimetres in size.

Its teeth have a tall, narrow and sharply pointed central cusp, surrounded by small side points. Lateral teeth commonly develop two pairs of cusplets, while fine vertical folds can occur around the base of the crown. The broad root has a distinctive deep groove through its centre.

The species occurs in the Early Eocene London Clay Formation and has been documented from Burnham-on-Crouch. Because the teeth are extremely small, they can easily be overlooked without careful searching or fine sieving.

A good identification should combine the tiny size, tall sharp central point, multiple side points, basal vertical folds and broad grooved root, rather than relying on any one feature alone.

Geological Age & Range Notes

Late Palaeocene to Late Eocene, with records extending from the Thanetian through the Ypresian and Lutetian, and material attributed to the species also occurring in younger Eocene deposits.

Fossil Material

Tooth

Known Localities

Diagnostic Features

  • The teeth are very small, usually only a few millimetres high.
  • The centre of the tooth forms a tall, narrow and very sharply pointed main cusp.
  • The main cusp is relatively thick from front to back, despite looking narrow when viewed from the front.
  • Front teeth are generally upright and fairly symmetrical.
  • Teeth from farther around the jaw become broader and less symmetrical, with the main point leaning slightly towards one side.
  • Beside the main point are small pointed side cusplets.
  • Front teeth may have only one obvious side point on each side, and occasionally one side may be much less developed than the other.
  • Teeth from farther around the jaw normally develop two pairs of side points. The second pair can be small and partly joined to the first pair.
  • Exceptionally, a tooth may even develop a tiny additional third side point towards the outer edge.
  • The side points usually point upwards towards the main cusp, rather than strongly outwards.
  • The front surface of the crown commonly has fine vertical folds or ridges near its base.
  • These little ridges are especially noticeable underneath and beside the main point.
  • Fine folds can also occur around the bases of the side points on the opposite face of the tooth.
  • Most of the main cusp itself is smooth, particularly towards the tip.
  • The cutting edges are smooth and have no serrations.
  • The root is broad and relatively substantial compared with the small crown.
  • Viewed from underneath, the bottom of the root is fairly flat.
  • A deep groove runs through the centre of the root, dividing it into two sides.
  • On the inner face of the tooth, the root forms a noticeable rounded central bulge.

Identification Notes

Pachyscyllium gilberti, traditionally called Premontreia gilberti, was a small catshark whose fossil record is known largely from isolated teeth.

Despite their tiny size, complete teeth are quite distinctive.

A good specimen should show a tall pointed central cusp surrounded by small side points, giving it a miniature multi-pointed appearance.

Look at the side points

The number and arrangement of the side points is particularly useful.

Teeth from near the front of the mouth may have only one clear pair, while lateral teeth generally develop two pairs of well formed cusplets.

The second pair sits outside the first and may be considerably smaller.

This means that a complete lateral tooth can appear to have:

small point + larger side point + tall central point + larger side point + small point.

Recent material confidently assigned to P. gilberti has been recognised partly by this combination of a tall sharp central cusp and two pairs of well developed side cusplets.

Look for the vertical folds

Another useful feature is the decoration around the bottom of the crown.

The main cusp is mostly smooth, but at its base there are often several fine vertical ridges or wrinkles.

These are easiest to see on a clean, well preserved tooth under magnification.

Some specimens have very obvious folds while others show much weaker decoration, so their absence should not automatically rule out P. gilberti. Variation in the strength of these ridges has been documented within material attributed to the species.

Teeth change around the jaw

As with many sharks, the teeth do not all look identical.

Front teeth are generally:

  • taller and narrower
  • fairly symmetrical
  • more upright
  • equipped with fewer or less developed side points

Side teeth become:

  • broader
  • slightly tilted
  • less symmetrical
  • equipped with more strongly developed side points

Casier’s original material already showed considerable variation between anterior and lateral teeth, including the development of additional cusplets in the lateral positions.

Do not confuse the side points with damage

Because these teeth are so small, the outer cusplets are very easily broken away.

A lateral tooth originally possessing two pairs of cusplets may therefore appear to have only one pair.

Look carefully for:

  • a broken edge where another point may have been
  • uneven development between the two sides
  • a small remaining bump beside the larger side point

The number of cusplets should therefore be considered alongside the central cusp, crown folds and root shape rather than being used alone.

The root is important

The root is particularly useful because it is one of the reasons the species is now placed in Pachyscyllium rather than Premontreia.

A complete specimen should have a fairly broad, substantial root with a flat underside and a deep groove running through the middle.

Recent taxonomic work specifically notes that differences in root morphology were important in transferring gilberti from Premontreia to Pachyscyllium.

For this reason, specimens consisting only of the crown should be identified more cautiously.

Similar small catshark teeth

Small Palaeogene catshark teeth can be surprisingly difficult to separate because several species have:

  • a pointed central cusp
  • small side cusplets
  • smooth cutting edges
  • folds around the base of the crown

For Pachyscyllium gilberti, concentrate on the combination of features rather than any single character:

very small size + narrow sharply pointed main cusp + well developed multiple cusplets + vertical basal folds + characteristic broad grooved root.

A complete lateral tooth showing two pairs of side cusplets is particularly useful for identification.

Broken specimens

If the root is missing and only the main cusp survives, confident identification becomes much more difficult.

A broken crown may still be recognised as a small catshark tooth, but identifying it specifically as P. gilberti may not be justified.

For poor specimens, Pachyscyllium sp. or Pachyscyllium cf. gilberti would be safer.

London Clay identification

The species is a recognised component of the London Clay shark fauna, and specimens are documented from Burnham-on-Crouch.

Because the teeth are normally only a few millimetres in size, they are much more likely to be recovered from fine sieved material than noticed during ordinary surface collecting.

A complete London Clay specimen showing a tall sharp central cusp, multiple side cusplets, basal crown folds and the correct root structure is a strong Pachyscyllium gilberti candidate.

Quick recognition

Look for:

tiny tooth + tall sharp central point + usually two pairs of small side points on lateral teeth + fine vertical folds around the bottom of the crown + broad root with a deep central groove.

References & Literature

  • Casier, E. (1946). La faune ichthyologique de l’Yprésien de la Belgique. Mémoires du Musée Royal d’Histoire Naturelle de Belgique 104: 1–267. Original description as Scyliorhinus gilberti.
  • Casier, E. (1966). Faune ichthyologique du London Clay. British Museum (Natural History), London. Major monograph covering the London Clay fish and shark fauna.
  • Cappetta, H. (1976). Sélaciens nouveaux du London Clay de l’Essex (Yprésien du Bassin de Londres). Geobios 9(5): 551–575.
  • Ward, D.J. (1980). The distribution of sharks, rays and chimaeroids in the English Palaeogene. Tertiary Research 3(1): 13–19. Important reference for the distribution of British Palaeogene sharks.
  • Cappetta, H. (1992). Carcharhiniformes nouveaux (Chondrichthyes, Neoselachii) de l’Yprésien du Bassin de Paris. Geobios 25: 639–646. Establishes the genus Premontreia.
  • Cappetta, H. (2012). Chondrichthyes: Mesozoic and Cenozoic Elasmobranchii: Teeth. Handbook of Paleoichthyology, Volume 3E. Transfers gilberti to Pachyscyllium on the basis of dental morphology, particularly the root.
  • Rodríguez, D., Ward, D.J. & Quezada, J.A. (2023). Paleontology and stratigraphic implications of a late Paleocene elasmobranch assemblage in Talcahuano, southcentral Chile. Andean Geology 50(2): 217–247. Provides a modern description of the tooth morphology and demonstrates the species in the late Palaeocene.
  • De Schutter, P.J. & Steurbaut, E. (2025). Taxonomic revision and new elasmobranch records from the Wemmel Sand and Asse Clay members, base of the Maldegem Formation. Geologica Belgica 28(3–4): 117–131. Provides useful modern diagnostic characters and follows the combination Pachyscyllium gilberti.