Three extant genera of freshwater thalassiosiroid diatoms from Middle Eocene sediments in northern Canada

The evolutionary history of diatoms is only constrained partially by the fossil record. The timing of several key events, such as initial colonization of freshwater habitats by marine taxa, remains poorly resolved. Numerous specimens of the genera Cyclotella, Discostella, and Puncticulata (Ochrophyt...

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Bibliographic Details
Published in:American journal of botany 2009-02, Vol.96 (2), p.487-497
Main Authors: Wolfe, Alexander P, Siver, Peter A
Format: Article
Language:English
Subjects:
Algae
Botany
Cell walls
Cyclotella
Diatoms
Discostella
Eocene
Evolution
Evolutionary biology
fossil diatoms
Fossils
Fresh water
fultoportula
Genera
Geological time
Giraffes
morphology
Peridotite
Phycology
Puncticulata
Sediments
Taxa
Thalassiosirales
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Summary:The evolutionary history of diatoms is only constrained partially by the fossil record. The timing of several key events, such as initial colonization of freshwater habitats by marine taxa, remains poorly resolved. Numerous specimens of the genera Cyclotella, Discostella, and Puncticulata (Ochrophyta: Thalassiosirales) have been recovered in Middle Eocene lacustrine sediments from the Giraffe Pipe locality in the Northwest Territories, Canada. These diatoms extend the fossil record of the family Stephanodiscaceae to at least 40 million years before present (Ma) and thus provide a new evolutionary milepost for the thalassiosiroid diatoms, an important clade of centric diatoms with global representation in both marine and freshwater environments. The quality of the fossil material enables detailed investigations of areolae, fultoportulae, and rimoportulae, revealing direct morphological affinities with a number of extant taxa. These observations extend the antiquity of several characters of phylogenetic importance within the thalassiosiroid diatoms, including the fultoportula, and imply that the entire lineage is considerably older than prior constraints from the fossil record, as suggested independently by several recent molecular phylogenies.
ISSN:0002-9122
1537-2197
DOI:10.3732/ajb.0800307