Article: An ontogenetic sequence of coccoliths from the Late Jurassic Kimmeridge Clay of England

The Kimmeridge Clay of Kimmeridge Bay, Dorset, UK, includes several stone bands which electron microscopy shows are coccolith limestones dominated by the species Watznaueria fossacincta. The assemblage includes not only fully grown coccoliths but also specimens at earlier growth stages, including proto-coccolith rings. A complete ontogenetic sequence can thus be reconstructed. This interpretation is supported by the occurrence of early growth stages inside coccospheres, i.e. intracellular coccoliths preserved in the process of growth. The coccolith formation process appears to have been directly comparable to that known in living coccolithophores. The early growth phases have previously been described as separate species; these can now be put in synonymy.