24 May 2019
The survivors of Earth’s worst mass extinction
Published online 23 December 2018
Plant fossils in Jordan indicate key terrestrial species evolved earlier than previously thought and appear to have survived a mass extinction some 250 million years ago.
Tropical seas have long been considered evolutionary cradles, where life forms have been able to evolve and adapt at higher rates than at other latitudes. But it has not been clear if the evolution of terrestrial plant and animal life has followed the same pattern. This is due to a lack of evidence: although drier equatorial conditions often drive evolutionary adaptations, they are not conducive to fossil preservation.
Now, Patrick Blomenkemper and co-workers at the University of Münster, Germany, together with scientists in Jordan and the USA, have uncovered beautifully preserved 250 million-year-old Permian equatorial lowland plant fossils from a site beside the Dead Sea in Jordan. The geologic Permian period extended from 289.9 to 252.2 million years ago. The greatest natural disaster of Earth’s history happened at its end and led to the extinction of 90% of the planet’s species.
“In many regions of the world, Upper Permian sediments are marine in origin, without plant fossils,” explains Blomenkemper. “In the Umm Irna Formation [in Jordan], we discovered fluvial deposits with abundant plant fossils, including three major lineages thought originally to have evolved later, in the Triassic.”
The fossils include the oldest recorded from the conifer family Podocarpaceae and two extinct groups of seed-bearing plants, and contain leaves with preserved cuticles. Surprisingly, the plants appear to have thrived throughout the Permian-Triassic boundary.
The results suggest that land plants, and perhaps the communities they supported, were more resilient than previously believed.
“Now that we have a better idea of where to look for the earliest records of new plant groups, we can target searches for similar equatorial cradles around the world,” says Blomenkemper.
Blomenkemper, P. et al. A hidden cradle of plant evolution in Permian tropical lowlands. Science 362, 1414–1416 (2018).