A new genus and species of fimbriid bivalve from the Kimmeridgian of the western Pontides, Turkey, and the phylogeny of the Jurassic Fimbriidae

A new lucinoidean genus and species, Cerkesia contiae gen. et sp. nov., from the Kimmeridgian carbonate platform deposits of the Çerkes area (western Pontides, Turkey), is described and placed in the family Fimbriidae. Morphological comparisons reveal similarities with Fimbria, Cyclopellatia and Sphaera. A phylogenetic analysis supports the monophyly of the family. Similarities between Cerkesia and Fimbria determine inclusion of these genera in the same clade. The unusual features characterizing Cerkesia closely relate it to Cyclopellatia. Sphaera belongs to a different clade and its similarities with Cerkesia are owing to convergent and plesiomorphic characters. Cerkesia was a slow and shallow burrower. The morphology of the anterior adductor scar suggests a mode of life comparable to that of Fimbria but other features indicate adaptive strategies typical of the Lucinidae. The associated fossils and facies reveal that Cerkesia lived in soft and sandy substrates of quiet and protected areas of the carbonate platform under stressful environmental conditions. The appearance of Cerkesia in the western Pontides marks the eastward expansion of a clade that developed principally in the European seas during the Late Jurassic while the Sphaeriola-Sphaera clade was confined to the southernmost Tethyan margin.