Unique chromosomes found in fern fossil

Swedish researchers thrilled with discovery.

Fossils are key in determining how past life existed. However, it is rare that a fossil is found that is so well-preserved, cell material remains in tact. Researchers from Lund University and the Swedish Museum of Natural History have made a unique discovery in a well-preserved fern that lived over 180 million years ago. Thanks to its burial in a sudden volcanic explosion, the fossil contains both undestroyed cell nuclei and individual chromosomes.

The fern was found in Skåne, a region of southern Sweden. The plant lived approximately 180 million years ago during the Jurassic period, when the area had a tropical climate, and was dominated by dinosaurs. Due to the nature of the preservation of the fern, the area is now attracting attention in the research community.

Since its discovery, the plant has been studied using many different microscopic techniques, X-rays, and geochemical analyses. Examinations have shown that the plant was preserved instantaneously following a sudden volcanic lava flow.

“The preservation happened so quickly that some cells have even been preserved during different stages of cell division,” said Vivi Vajda, a professor of geology at Lund University.

Due to the sudden preservation, the ‘sensitive’ components of the cells remained nearly intact. Researchers found cell nuclei, cell membranes, and individual chromosomes—all structures that are extremely rare finds in fossils.

“This naturally leads us to think that there must be more to discover. It isn’t hard to imagine what else could be encapsulated in the lava flows [in Skåne],” Vajda said.

A farmer discovered the unique fossil in the 1960s, and then donated it to the Swedish Museum of Natural History. The fossil remained untouched for over forty years before it came to the attention of the researchers.

Vajda, along with two researchers from the Swedish Museum of Natural History,  has also dated the rocks that were found surrounding the fossil by studying the spores and pollen preserved within them. The research showed evidence of varied vegetation that suggests a hot, humid climate at the time of the volcanic eruption.

Chromosomes carry the genetic information of an organism. By analyzing the fossil stem, measuring the dimensions of the nuclei during interphase (a stage of cell division) in the fossil’s pith, and the parenchyma cells (a type of cell that differentiates into other plant cell types), the researchers found that the chromosomes match those of its living relative, Osmundastrum cinnamomeum. The plant, otherwise known as the cinnamon fern, is found throughout Canada and the eastern United States. Through this investigation, researchers have been able to show that the royal ferns have outstanding evolutionary stability.

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