Duplexdens macropomus

Duplexdens macropomus

(Agassiz, 1844)

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

Summary

Duplexdens macropomus was a predatory scombrid-grade fish with a highly differentiated dentition. Its jaws carried two very different tooth sizes: tiny outer teeth and much larger inner teeth, giving the mouth a strong grasping apparatus suited to holding relatively large or slippery prey. The long jaws and sizeable gape support an active predatory role in the London Clay marine ecosystem.

Three-dimensional skulls preserve a wealth of detail, including coarse frontal sculpture and an elongate lachrymal bone. The mixture of small and enlarged teeth is not merely decorative morphology; it reflects a feeding system in which prey could be seized by larger inner teeth while smaller teeth helped retain it. Exact prey species are unknown, but fishes and other nekton are reasonable candidates.

Quick Identification

Look for: a long-jawed scombrid skull with two conspicuously different tooth series — minute outer conical teeth and much larger inner semiconical teeth with basal striations — plus coarse longitudinally oriented sculpture on the frontals.

Diagnostic Features

  • Outer jaw row consists of very small conical teeth, generally under about 1 mm.
  • Inner row contains much larger semiconical teeth, around several millimetres high, with striated bases.
  • Lachrymal bone is elongate and longer than the diameter of the orbit.
  • Frontals carry coarse rugose ornament arranged broadly parallel to the skull axis.
  • Anterior ethmoid margin is distinctly indented or shallowly forked.

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