Egertonia isodonta

Egertonia isodonta

Cocchi, 1864

Common name Bonefish
Fossil group Bony Fish
Order Albuliformes
Family Phyllodontidae
Genus Egertonia
Taxonomic status Accepted
Geological age Thanetian and Ypresian

Summary

Egertonia isodonta was a phyllodont fish characterised by broad dental plates used for crushing. Rather than relying on individual piercing teeth, it carried dense batteries of rounded teeth that formed a durable grinding surface. This feeding apparatus strongly suggests consumption of hard-shelled benthic prey such as molluscs or crustaceans, although the exact diet is inferred from tooth form rather than preserved stomach contents.

Phyllodont tooth plates are among the more readily recognisable bony-fish remains from Eocene marine deposits because the densely packed dentition survives after the rest of the skeleton is lost. Egertonia therefore represents a specialised durophagous component of the London Clay food web.

Quick Identification

Look for: a compact tooth plate made of many closely packed rounded to low-domed teeth, with the individual crowns comparatively similar in size and arranged as a dense crushing pavement rather than in a single jaw row.

Diagnostic Features

  • Teeth are crowded into a broad, multi-rowed crushing plate.
  • Individual crowns are rounded to low-domed rather than pointed or blade-like.
  • Tooth sizes are comparatively even across much of the functional surface.
  • Crowns are tightly apposed, leaving little open bone between neighbouring teeth.
  • Underlying plate is thick and robust, supporting successive replacement teeth beneath the functional surface.

Fossil Details

Typical size
Known chiefly from isolated teeth and tooth-bearing material; whole-body length is not securely constrained.
Fossil material
Tooth, Tooth Plate
Preservation
Dental material is often separated from the jaw and may be heavily worn. Crushing crowns can lose their original relief and pointed teeth can lose tips, edges or basal structures; incomplete specimens should be identified conservatively.

Similar Species

Recorded Fossil Sites

Synonyms & Previous Names

Egertonia gosseleti

References

  • Casier, E. (1966). Faune ichthyologique du London Clay. 496 pp.. Trustees of the British Museum (Natural History), London View reference
  • Ebersole, J.A.; Cicimurri, D.J.; Stringer, G.L. (2019). Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths. European Journal of Taxonomy, 585, 1–274 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
  • Ward, D.J. (1978). The Lower London Tertiary (Palaeocene) succession of Herne Bay, Kent. Report of the Institute of Geological Sciences. Institute of Geological Sciences View reference
Last Reviewed
20 August 2026 Reviewed by Sam Harris