Sunday, March 23, 2014

180 million year old fern fossil discovered

Photo from the Science paper, credit: Benjamin Bomfleur
Several Swedish biologists (from Lund University and the Swedish Museum of Natural History) have published a paper in Science documenting an exquisitely preserved, 180 million year old fern fossil! The Jurassic-era fossil is a member of the family Osmundaceae, which includes modern taxa like cinnamon fern (Osmundastrm cinnamomea), royal fern (Osmunda regalis), and interrupted fern (Osmunda claytoniana), all of which are widespread in the temperate northern hemisphere (and are pictured below). The fossil's exquisite preservation is attributed to rapid burial during volcanic activity.

It has long been known that modern members of Osmundales don't vary much morphologically compared to ancient forms – fossilized members of the order dating to the early Mesozoic (ca. 220 million years ago) are remarkably similar in several aspects of their morphology to modern species. The new fossil goes a step further: it contains intact cells, and even individual chromosomes, that the researchers were able to visualize with various types of microscopy. The fossil species had the same number of chromosomes and roughly the same predicted DNA content in the nucleus as modern cinnamon fern. This suggests that the lineage has not experienced significant upheaval in DNA content, through whole-genome duplication (polyploidy) or extensive gene loss, in the last 180 million years. The authors note that to date, most of what we know about ancient fern genome size is due to extrapolation from living taxa; this new fossil has permitted the first direct observations of paleo-DNA content in a fern.

Coverage of the new fossil online:
From Lund University

The paper (requires a subscription): Bomfleur, B., S. McLoughlin, and V. Vajda. 2014. Fossilized nuclei and chromosomes reveal 180 million years of genomic stasis in royal ferns. Science 343: 1376–1377.

If you want to read more about relationships of Osmundales (also requires a subscription): Metzgar, J.S., J.E. Skog, E.A. Zimmer, and K.M. Pryer. 2008. The paraphyly of Osmunda is confirmed by phylogenetic analyses of seven plastid loci. Systematic Botany 33: 31-36.

Osmundastrum cinnamomea 
Osmunda regalis
Osmunda claytoniana

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