Pompeii of prehistoric plants

Nearly 300 million years ago, a volcanic eruption in northern China smothered a nearby swamp under half a metre of ash. Though cataclysmic for the plants living there, it was a boon for palaeontologists, who uncovered the exquisitely preserved specimens millions of years later in 2006.

Now, new analysis of these spectacular fossils has yielded evolutionary insights, revealing that some of the preserved trees – called Noeggerathiales – are the ancestors of the seed-bearing plants that dominate the Earth today.

Noeggerathiales was a peat-forming order of plants that lived from 325 to 251 million years ago, before the rise of the dinosaurs and while the Earth’s lands were arranged into the supercontinent Pangea. Specimens were first discovered in the 1930s, but a dearth of well-preserved fossils prevented scientists from accurately placing them in the plant kingdom; some even considered the plants to be an evolutionary dead-end.

But not anymore.

“Thanks to this slice of life preserved in volcanic ash, we were able to reconstruct a new species of Noeggerathiales that finally settles the group’s affinity and evolutionary importance,” says co-author Jason Hilton, from the University of Birmingham, UK.

Hilton was part of an international research team led by palaeontologists at the University of Birmingham and the Nanjing Institute of Geology in China.

In their paper in the journal PNAS, the team describe how they studied a completeNoeggerathiales fossil preserved in a bed of volcanic ash 66 cm thick, formed 298 million years ago. This unique preservation – with ash covering a large expanse of forest and swamp in just a few days – provides a snapshot of a moment in time, just as the excavation of Pompeii provided a glimpse of ancient Roman life.

The team found that Noeggerathiales are more closely related to seed plants than to other fern groups, even though they appear fern-like, with complex cone-like structures evolved from modified leaves.

They also deduced that the ancestral lineage of seed plants diversified during the Devonian, Carboniferous and Permian periods (approximately 419–252 million years ago), and didn’t die out as previously thought.

The order of Noeggerathiales, however, went extinct around 251 million years ago when massive environmental changes swept across the globe during the Permian-Triassic extinction event.

“The fate of the Noeggerathiales is a stark reminder of what can happen when even very advanced life forms are faced with rapid environmental change,” Hilton notes.