Journal of Paleontology

ABTRACT--Available museum collections have been utilised for a functional analysis of common members of the bivalve fauna of the Cretaceous Chalk Formation of England. It is concluded that many members of the fauna were able to inhabit their unusual environment by virtue of specialised adaptations. There is an apparent paucity of infaunal bivalves in true Chalk lithology, and the fauna is dominated by epifaunal animals. Adaptations found in members of the epifauna fitting them for life on a soft fine-grained substrate include the probable life habits of swimming, byssal attachment, cementation, and secretion of a gryphaeate lower valve. A remarkable case of parallel adaptation in Spondylus spinosus (J. Sowerby) and Arctostrea colubrina ricordeana (d'Orbigny) is related to their inferred adult life habit of lying free on the soft substrate. Specialised 'snowshoe' spines were secreted by these animals to help prevent their sinking into the Chalk ooze. An appendix contains a detailed functional analysis of Spondylus spinosus and Plicatula inflata (Sowerby), and it is demonstrated for the first time that Spondylus spinosus possessed an early ontogenetic stage of direct cementation.