Trochosira polychaeta: a colonial diatom from the late Cretaceous exhibiting two contrasting chain-linking mechanisms and a wide range of preservation

The fossil species Trochosira polychaeta Strelnikova, exhibits a wide range of preservational states that has led to contrasting interpretations with regard to its resting stage or vegetative cell status. Within shallow-buried, well preserved diatomites from the Alpha Ridge of the Arctic Ocean, a continuum of dissolution effects are documented and a vegetative cell status is clearly indicated. The chains are formed by a central linking process but complex marginal structures also constitute a complementary linking mechanism. The double linkage may have supported the integrity of the colonial chains and provided a mechanism for enhanced nutrient uptake. The presence of two distinct types of linking might also represent a stage in a transition from the Cretaceous when central linking structures were common, through the Cenozoic to the modern with more common linking through marginal structures