A violent death has led to a remarkably lucky preservation. Researchers in Sweden have discovered ferns that were buried suddenly in a volcanic eruption during the Jurassic period. The sudden burial has preserved stunning details of the fern, down to showing the plant's chromosomes being separated during cell division. In fact, the details are sufficient to determine that its genome hasn't undergone major changes in at least 180 million years.

The fossil was found in a volcanic deposit in southern Sweden. It belongs to a group of plants called the royal ferns (technically, the Osmundaceae). The group, which includes a number of different species, was already known as a bit of a living fossil, since some of its distinctive features have been seen on plants that are 220 million years old, and a variety of other fossil species look indistinguishable from modern forms.

The samples themselves are simply stunning. Not only are the internal details of various plant tissues preserved, but internal details of individual cells have been preserved. These include cells at various stages of the cell division process; darker, dense material shows the chromosomes being split up between the two incipient daughter cells.

Not only are these details stunning in a 190-million-year-old sample, they allow researchers to make inferences about the amount of DNA present. There's a strong relationship between the size of the nucleus and the amount of DNA that it contains. By measuring the nucleus in the fossils, the researchers were able to determine that the DNA content of the cells hasn't changed much in the last 180 million years, either.

That doesn't mean that there are no changes in the DNA itself—there are other living fossils that show evidence of rapid evolution despite no overt physical changes. But it does show that once nature comes up with an architecture that works, it's prone to stick with it—even for millions of years.

Science, 2014. DOI: 10.1126/science.1249884 (About DOIs).