Scientists have uncovered evidence that flowering plants were already the reigning giants of Earth's forests nearly 10 million years before the catastrophic asteroid impact that ended the age of dinosaurs—upending a long-held assumption about when these plants took over the planet.
A cache of plant fossils preserved in volcanic ash deposits in New Mexico reveals that a thriving, mature forest dominated by flowering plants existed 74.6 million years ago in the Late Cretaceous period. Many of these ancient plants produced relatively large, fleshy fruits, complete with seeds that were significantly bigger than those found at other fossil sites from the same era. The discovery, led by UC Berkeley paleobotanists and published in the journal Science, paints a picture of dense, modern-style forests far earlier than scientists believed possible.
"Our results show that, at least in some hot and humid environments during the Late Cretaceous, well before the extinction boundary by 10 million years, angiosperms were already investing more resources into individual diaspores and forming dense forests," said lead author Jaemin Lee, a doctoral student at UC Berkeley.
The New Mexico site is exceptionally rare. Unlike most fossil deposits, where plant material washes into rivers or lakes over time, the ancient volcanic ashfall buried this entire inland forest within days, preserving it in extraordinary detail—researchers call it a "botanical Pompeii." At the base of the solidified ash layer, ground cover plants remain in place; higher up, leaves in all orientations reveal the forest canopy falling to the forest floor.
"You can think of it as like a botanical Pompeii, where ashfall deposits preserve everything in position and we can reconstruct the forest structure," Lee explained.
The difference in seed size is striking. At other Cretaceous fossil sites, the average seed or fruit—known as a diaspore—was roughly the size of a poppy seed. At this New Mexico site, the average diaspore was comparable to a large blueberry, representing more than a hundredfold increase in volume. This matters because large, fleshy fruits require more energy to produce, and scientists had assumed that plants only began investing in such energy-intensive reproduction after the dinosaurs vanished, when mammals like rodents and bats became available to help disperse seeds.
The fossil forest included large-trunked flowering trees—laurel relatives and palms among them—growing alongside more ancient lineages of ferns and redwoods. The discovery suggests that flowering plants, which now comprise all the food humans eat, from staple grains to avocados, were far more ecologically successful in the Cretaceous than previously understood.
"These diaspores are preserved together with various leaves and flowers, brought from the canopy down to the forest floor by the ashfall," said Professor Cindy Looy of UC Berkeley's Department of Integrative Biology and curator in the UC Museum of Paleontology.
The findings add nuance to the story of how flowering plants—a group that arose roughly 135 million years ago and was initially small, weedy, and inconspicuous—eventually came to dominate every continent on Earth. The new evidence suggests their rise was already well underway while dinosaurs still walked—and ate—the landscape.