Pycnodontiformes are an extinct order of marine fish which have no living members but survived from the Late Triassic through to the Eocene. This means that those species of Pycnodontiformes found in the London Clay are amongst the final species to have represented this group.

One distinguishing characteristic of this group is the presence of flat, crushing teeth on the both the lower and upper jaws which helped with crushing the exoskeletons of their prey such as crabs, urchins or molluscs.

An example of a complete Pycnodontiformes featured here is Neoproscinetes penalvai from the Cretaceous of Brazil.

Photo by Ghedoghedo – specimen in the Palaeontological museum, Munich