The Mode of Life in the Genus Pholadomya as Inferred from the Fossil Record

Abstract

The paper is an attempt to reconstruct the mode of life of Pholadomya bivalves, very common in the fossil record, particularly that of the Jurassic. The only extant representative of the genus is extremely rare and very poorly known. Materials from the Polish Jurassic deposits (Bajocian–Kimmeridgian; Western Pomerania and Polish Jura) and literature data were used for the reconstruction. Specifically, observations on the anatomy, taphonomy, and diagenesis of the specimens examined as well as lithology of the deposits housing the specimens were used. Shell anatomy characteristics are known for their particular utility in mode of life reconstructions, although the extremely thin-shelled and coarsely sculpted bivalves, such as the Pholadomya examined, have not been studied so far. The reconstruction suggest a diversity of the mode of life, coincident with the morphological differences between the Pholadomya species. At least the adults of anteriorly flattened species are inferred to have lived extremely deeply buried in the sediment, and were hardly mobile. The smaller, more oval in shape, species were more mobile, and some of them are thought to have preferred life in shelters, should those be available. In addition, the function of the cruciform muscle, other than that considered so far, is suggested.