Palaeocybium proosti

Palaeocybium proosti

(Storms, 1897)

Common name Mackerel / tuna
Fossil group Bony Fish
Order Scombriformes
Family Scombridae
Genus Palaeocybium
Taxonomic status Accepted
Geological age Ypresian

Summary

Palaeocybium proosti was a predatory mackerel relative with a formidable jaw apparatus. Its dentition included tightly packed, laterally compressed teeth with strong cutting edges, indicating a fish adapted to grasping and slicing mobile prey. Fishes and other nekton are the most plausible food items, although no direct feeding remains are preserved.

The species is known from jaws, teeth and cranial material. Modern revision of its anatomy has helped separate it from historical broad assignments to living-style mackerel genera. The heavy, carinate teeth show that the early Eocene scombrid radiation included predators with considerably more robust dentitions than those of many modern plankton-feeding or small-prey mackerels.

Quick Identification

Look for: robust laterally compressed scombrid teeth that are thick through the middle and carry sharp carinae extending down to the base; complete jaws show a differentiated series with smaller outer teeth and larger cutting teeth inside.

Diagnostic Features

  • Teeth are laterally compressed with sharp cutting carinae on the crown margins.
  • Carinae extend to the tooth base rather than fading well above it.
  • Tooth bases are not strongly constricted below the crown.
  • Larger teeth are thick medially and show a central pulp cavity in broken examples.
  • Jaws carry differentiated tooth rows, with larger inner cutting teeth and smaller outer teeth.

Fossil Details

Preservation
London Clay fish skulls are commonly incomplete, compressed, pyritised or enclosed in concretions. Thin cranial margins and projecting processes are easily lost, and separated bones can be difficult to orient; species-level identification is strongest when several adjoining diagnostic bones are preserved together.

Recorded Fossil Sites

References

  • Casier, E. (1966). Faune ichthyologique du London Clay. 496 pp.. Trustees of the British Museum (Natural History), London View reference
  • Friedman, M.; Beckett, H. T.; Close, R. A.; Johanson, Z. (2016). The English Chalk and London Clay: two remarkable British bony fish Lagerstätten. Geological Society, London, Special Publications, 430(1), 165–200. Geological Society of London, London View reference
  • Monsch, K. A. (2005). Revision of the scombroid fishes from the Cenozoic of England. Transactions of the Royal Society of Edinburgh: Earth Sciences, 95(3–4), 445–489 View reference
Last Reviewed
20 August 2026 Reviewed by Sam Harris