Fideliacyclus wombatiensis gen. et sp. nov. – a Paleocene non-marine centric diatom from northern Canada with complex frustule architecture
2016
Siver, Peter A. | Wolfe, Alexander P. | Edlund, Mark B.
Marine diatoms began colonizing freshwater habitats in the early Cenozoic, or possibly earlier, becoming well established by the Eocene. However, because of a sparse fossil record, little is known about the earliest diatom representatives that signalled this important ecological and evolutionary event. We describe a new centric diatom genus, Fideliacyclus , from lake sediments deposited during the Paleocene in the Canadian Arctic. This organism, one of the oldest known freshwater diatoms reported to date, has a unique, highly complex wall structure composed of areolae with large, bulbous, spherical shaped chambers that are open to the external environment but rest on a solid siliceous surface referred to as the solum, and are surrounded by an open space, or hypocaust. The solum is only perforated by marginal labiate processes, which largely isolates the protoplast from ambient conditions hence limiting exchange; this may have represented an adaptive response to living in freshwater. Given the complement of microfossils found in the fossil locality, the lake was an unambiguously softwater, slightly acidic, limnic system of moderate nutrient content. Although the exact taxonomic position of Fideliacyclus remains uncertain, it appears to be most closely allied to Actinocyclus (Class: Coscinodiscophyceae) or possibly Spumorbis given the range of synapomorphies.
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