Aetomylaeus dixoni

Aetomylaeus dixoni

(Agassiz, 1843)

Common name Eagle ray
Fossil group Sharks & Rays
Order Myliobatiformes
Family Myliobatidae
Genus Aetomylaeus
Taxonomic status Accepted
Geological age Lutetian, Thanetian, and Ypresian

Summary

Aetomylaeus dixoni was an eagle ray adapted for active swimming above the seafloor while feeding on hard prey below. Eagle rays combine broad wing-like pectoral fins with powerful crushing dentitions, allowing them to travel efficiently between feeding areas and exploit animals protected by shells or hard exoskeletons.

Its broad pavement teeth were suited to crushing and grinding. Molluscs and crustaceans are therefore the most plausible major prey, although the exact diet cannot be demonstrated from isolated fossil teeth alone.

The species is known principally from dental-plate material rather than complete skeletons. Even so, the teeth preserve a clear ecological signal: A. dixoni was a specialised durophagous ray occupying the benthic-feeding part of the early Eocene marine ecosystem.

Quick Identification

Look for: a broad, low eagle-ray crushing tooth or dental-plate element that is much wider than it is high, with a flattened wear surface and a root divided into numerous narrow parallel lamellae; heavily worn or incomplete plate fragments should normally remain Myliobatidae indet.

Diagnostic Features

  • Median dental elements are strongly transversely elongated and form part of a crushing pavement.
  • Crown is low with a flattened to gently convex occlusal surface rather than a projecting cusp.
  • Root is polyaulacorhize, divided into numerous narrow parallel lamellae beneath the crown.
  • Labial and lingual crown-surface morphology is useful when well preserved but can vary and wear substantially.
  • Associated plate geometry and complete tooth proportions are more reliable than isolated lateral fragments for species-level identification.

Fossil Details

Typical size
Individual dental elements are millimetre- to centimetre-scale; median teeth are much wider than lateral elements and complete plate fragments can be larger.
Fossil material
Tooth, Tooth Plate
Preservation
Dental-plate elements commonly lose their root lamellae or break into rectangular fragments, destroying the original width-to-length proportions. Surface wear can also remove crown detail. Fragments lacking enough of the outline or plate architecture should be identified as Myliobatidae indet. rather than forced to this species.

Similar Species

Recorded Fossil Sites

Synonyms & Previous Names

Myliobatis dixoni

References

  • Dineley, D. & Metcalf, S. (1999). Fossil Fishes of Great Britain. Geological Conservation Review Series, 675 pp.. Joint Nature Conservation Committee, Peterborough View reference
  • Hovestadt, D.C.; Hovestadt-Euler, M. (2013). Generic Assessment and Reallocation of Cenozoic Myliobatinae based on new information of tooth, tooth plate and caudal spine morphology of extant taxa. Palaeontos, 24, 1–66 View reference
  • Rayner, D.; Mitchell, T.; Rayner, M. (2009). London Clay Fossils of Kent and Essex. 228 pp.. Medway Fossil and Mineral Society, Rochester, Kent View reference
  • Reinecke, T.; Mollen, F.H.; Gijsen, B.; D’Haeze, B.; Hoedemakers, K. (2024). Batomorphs (Elasmobranchii: Rhinopristiformes, Rajiformes, Torpediniformes, Myliobatiformes) of the middle to late Ypresian, early Eocene, in the Anglo-Belgian Basin (south-western North Sea Basin) – a review and description of new taxa. Palaeontos, 35, 1–172 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
  • Ward, D.J. (1980). The distribution of sharks, rays and chimaeroids in the English Palaeogene. Tertiary Research, 3(1), 13–19 View reference
Last Reviewed
19 August 2026 Reviewed by Sam Harris