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Fossilized Nuclei and Chromosomes Reveal 180 Million Years of Genomic Stasis in Royal Ferns

Science  21 Mar 2014:
Vol. 343, Issue 6177, pp. 1376-1377
DOI: 10.1126/science.1249884

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Cytologically Informative Fossils

Fossilization processes tend to destroy fine-cell structure but, exceptionally, Bomfleur et al. (p. 1376) have found examples of fossil ferns from the Jurassic in which subcellular structures, including organelles such as nuclei and chromosomes, are well-preserved. Comparative and quantative analyses show that these cells closely resemble the fossil nuclei of extant cinnamon ferns, Osmundastrum cinnamomea, which indicates that this group of ferns has remained virtually unchanged for 180 million years.

Abstract

Rapidly permineralized fossils can provide exceptional insights into the evolution of life over geological time. Here, we present an exquisitely preserved, calcified stem of a royal fern (Osmundaceae) from Early Jurassic lahar deposits of Sweden in which authigenic mineral precipitation from hydrothermal brines occurred so rapidly that it preserved cytoplasm, cytosol granules, nuclei, and even chromosomes in various stages of cell division. Morphometric parameters of interphase nuclei match those of extant Osmundaceae, indicating that the genome size of these reputed “living fossils” has remained unchanged over at least 180 million years—a paramount example of evolutionary stasis.

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