Elasmodus hunteri
Elasmodus hunteri
View age-specific evidence and explanation
| Age | Recorded Occurrences | Localities | Rarity |
|---|---|---|---|
| Thanetian | 1 | 1 | Not yet established |
| Ypresian | 2 | 2 | Not yet established |
These counts describe published LBPS Occurrence records with directly assigned, unambiguous geological-unit mappings—not specimen abundance. Records at restricted Localities and ambiguous or unsupported ages are excluded. Species-level age labels are not used as proof of an age-specific Occurrence.
Specimen-based rarity requires comparable, correctly identified physical fossils, geological provenance and publication permissions. It does not estimate your chance of finding a fossil or collecting access.
Quick Identification
What to look for
- Look for a substantial, continuous chimaeroid dental plate, with several hard biting patches rather than separate pointed teeth.
- On a lower-jaw (mandibular) plate, look for a broad hard patch near the inner edge of the jaw and a separate row of smaller patches towards the outer edge. Some of the rear patches form short, layered columns.
- Upper-jaw (palatine) plates have a different shape and arrangement, with several hard patches, some long and narrow. Do not use an upper-jaw diagram to identify a lower-jaw fragment.
Useful check
If the inner edge of a lower-jaw plate survives, locate the jaw’s central meeting line (symphysis). Compare the front-to-back width of the main inner biting patch with the gap between that patch and the meeting line. In described E. hunteri lower plates, the patch is at least as broad as that gap.
How to tell it apart
Amylodon eocenica is another plate-bearing chimaeroid worth checking. Compare the positions of the patches and the surviving jaw edges with published plates of both species; apparent size or a single layered chip cannot securely separate them.
Be careful
Wear and breakage can remove the jaw edge needed for the useful check. If too little remains to establish which jaw plate it is and how the biting patches relate to one another, record Elasmodus sp. or a broader chimaeroid rather than claiming E. hunteri.
Summary
In the seas that once covered parts of the London Basin, Elasmodus hunteri carried an unusually specialised set of jaws. This extinct chimaeroid had substantial dental plates combining hard crushing areas with narrow, layered strips of tooth tissue along their working edges. Researchers interpret that arrangement as an adaptation for processing resistant food. One study suggested that members of the wider genus Elasmodus might also have scavenged vertebrate remains, but that behaviour has not been demonstrated for E. hunteri.
Its story reaches back to the early days of scientific fossil collecting on the Isle of Sheppey. The species was described in 1843, and a lower-jaw plate from Sheppey later became central to fixing its identity. Such fossils preserve remarkable detail about the mouth, but the material reviewed for LBPS does not establish the animal’s full length, fins or colouring.
Nearly two centuries after it was named, the arrangement of these hard feeding surfaces still gives palaeontologists something to investigate: how a fish known largely from fragments of its jaws could have dealt with food in ways quite different from many other ancient fishes.
Diagnostic Features
- Mandibular mesial tritor: short anteroposteriorly, oriented approximately parallel to the symphyseal margin; in E. hunteri its anteroposterior breadth is at least comparable to the intervening gap to the symphysis.
- Mandibular outer tritors: laminated outer series; posterior elements may form several short separate columns.
- Palatine plates: massive with four to five tritors, including markedly elongated outer/mesial elements.
- Tissue organisation: tubular and lamellar hard-tissue components occupy position-dependent tritors.
- Vomerine plates: different arrangement, with subrectangular tritors and smaller outer laminated elements; do not infer palatine or mandibular diagnosis from vomerines.
- Identification limit: complete plate position and a coherent tritor pattern are needed for defensible species-level assignment; isolated hard-tissue fragments are insufficient.
Fossil Details
Similar Species
Recorded Fossil Sites
Beltinge Fish Bed
Lessness Shell Bed
London Clay Formation
Synonyms & Previous Names
Diagnostic Sources
Egerton (1843) established Elasmodus hunteri. Gurr (1962, p. 436) reported that the original Royal College of Surgeons type material had been destroyed during the Second World War and designated a mandibular plate catalogued as 43110, from the London Clay of Sheppey, as a neotype; he described it as right-sided. Averianov (2001, p. 295), attributing the designation to Casier (1966, p. 98), instead called the same specimen a left mandibular lectotype. These published accounts conflict in both the type term and the stated side. The earlier explicit neotype designation in Gurr should not be silently changed to lectotype; equally, laterality and the formal status of the designation warrant confirmation against Casier (1966) and the museum catalogue before any canonical type-material fields are populated. Ward (1973) and Averianov (2001) provide comparative dental-plate evidence. The disagreement does not, by itself, justify changing the species identification characters.
- Averianov, A.O. (2001). Systematics of the Cretaceous–Paleogene Chimaeroid Fish of the Genus Elasmodus (Chondrichthyes, Holocephali). Paleontological Journal, 35(3), 289–300 View reference
- Ward, D.J. (1973). The English Palaeogene Chimaeroid fishes. Proceedings of the Geologists' Association, 84(3), 315–330 View reference
References
- Averianov, A.O. (2001). Systematics of the Cretaceous–Paleogene Chimaeroid Fish of the Genus Elasmodus (Chondrichthyes, Holocephali). Paleontological Journal, 35(3), 289–300 View reference
- Dineley, D. & Metcalf, S. (1999). Fossil Fishes of Great Britain. Geological Conservation Review Series, 675 pp.. Joint Nature Conservation Committee, Peterborough View reference
- Gurr, P.R. (1962). A New Fish Fauna from the Woolwich Bottom Bed (Sparnacian) of Herne Bay, Kent. Proceedings of the Geologists' Association, 73(4), 419–447 View reference
- Jambura, P.L.; Solonin, S.V.; Cooper, S.L.A.; Mychko, E.V.; Arkhangelsky, M.S.; Türtscher, J.; Amadori, M.; Stumpf, S.; Vodorezov, A.V.; Kriwet, J. (2024). Fossil marine vertebrates (Chondrichthyes, Actinopterygii, Reptilia) from the Upper Cretaceous of Akkermanovka (Orenburg Oblast, Southern Urals, Russia). Cretaceous Research, 155, 105779. Elsevier View reference
- Ward, D.J. (1973). The English Palaeogene Chimaeroid fishes. Proceedings of the Geologists' Association, 84(3), 315–330 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