Basinotopus lamarckii

Basinotopus lamarckii

(Desmarest, 1817)

Common name Crab
Fossil group Crustaceans
Order Decapoda
Family Basinotopidae
Genus Basinotopus
Taxonomic status Accepted
Geological age Ypresian

Summary

Basinotopus lamarckii was a heavily built true crab with a compact, domed body. Like many bottom-living crabs it was probably an opportunistic omnivore, feeding on small invertebrates, carrion and other edible material it could find on or within the sediment.

Its tough shell and low, rounded shape would have suited life on the London Clay sea floor, where crabs had to deal with predators including fish, sharks and larger crustaceans. Fossils of robust crabs such as this help show that the early Eocene seabed supported a diverse community of active scavengers and predators.

Quick Identification

Look for: a broad, rounded and strongly domed crab carapace with deeply expressed regional divisions and a compact outline characteristic of Basinotopus.

Diagnostic Features

  • Carapace broad and rounded, with a strongly vaulted dorsal profile.
  • Gastric, cardiac and branchial regions are clearly expressed by grooves and swellings.
  • Overall outline is compact rather than elongate or frog-crab-like.
  • Dorsal surface shows pronounced regional relief rather than a nearly flat portunoid form.
  • Use the combined outline and regional pattern; incomplete central carapace fragments alone may not separate the species from other robust London Clay crabs.

Fossil Details

Typical size
Carapace typically centimetre-scale; a secure population range is not established.
Fossil material
Carapace, Claw / Chela
Preservation
The domed carapace may be compressed or split, and weathering can flatten the regional relief. Marginal breakage is common and can remove characters that help separate Basinotopus from other brachyurans.

Similar Species

Recorded Fossil Sites

Synonyms & Previous Names

Dromilites lamarckii

References

  • J. S. H. Collins; C. J. T. Mellish; A. J. Ross; P. R. Crabb; S. K. Donovan. (2020). A guide to the fossil Decapoda (Crustacea: Axiidea, Anomura, Brachyura) of the British Isles. Proceedings of the Geologists' Association, 131(1), 19–50 View reference
  • Thomas Bell. (1857). A monograph of the fossil malacostracous Crustacea of Great Britain. Part I. Crustacea of the London Clay. Monograph of the Palaeontographical Society, 10, i–viii, 1–44. Palaeontographical Society, London View reference
Last Reviewed
16 August 2026 Reviewed by Sam Harris