According to a new study of fossilized leaves of angiosperms (flowering plants excluding conifers) published in the journal PLoS Biology, the massive asteroid impact that wiped out the dinosaurs about 66 million years ago also boosted up fast-growing, deciduous plants.
Artistic reconstruction of a post-Chicxulub impact forest. Image credit: Donna Braginetz / Denver Museum of Nature & Science.
About 66 million years ago, a 10-km asteroid crashed into our planet near the site of the small town of Chicxulub in Mexico.
It left a crater more than 150 km across, and the resulting tsunami, wildfires, earthquakes and volcanism are widely accepted to have wiped out the dinosaurs and made way for the rise of the mammals.
The new study, carried out by U.S. scientists led by Dr Brian Enquist of the University of Arizona, reveals that the cataclysmic Chicxulub impact also decimated the evergreen flowering plants to a much greater extent than their deciduous peers.
The researchers were able to reconstruct the ecology of a diverse plant community thriving during a 2.2 million-year period (the last 1,400,000 years of the Cretaceous and the first 800,000 of the Paleogene) spanning the Chicxulub impact.
They found evidence that after the impact, deciduous angiosperms had replaced their slow-growing, evergreen peers to a large extent. Living examples of evergreen angiosperms, such as holly and ivy, tend to prefer shade, don’t grow very fast and sport dark-colored leaves.
“While it was known that the plant species that existed before the impact were different from those that came after, data was sparse on whether the shift in plant assemblages was just a random phenomenon or a direct result of the event,” said Benjamin Blonder, a researcher at the University of Arizona and the first author on the study.
“Our study provides evidence of a dramatic shift from slow-growing plants to fast-growing species.”
“This tells us that the extinction was not random, and the way in which a plant acquires resources predicts how it can respond to a major disturbance. And potentially this also tells us why we find that modern forests are generally deciduous and not evergreen.”
Dr Enquist, Mr Blonder and their colleagues studied a total of about 1,000 fossilized plant leaves collected from the Hell Creek Formation in southern North Dakota.
By analyzing leaves, which convert carbon dioxide into nutrients for the plant, they used a new approach that enabled them to predict how plant species used carbon and water, shedding light on the ecological strategies of plant communities long gone, hidden under sediments for many millions of years.
“We measured the mass of a given leaf in relation to its area, which tells us whether the leaf was a chunky, expensive one to make for the plant, or whether it was a more flimsy, cheap one,” Dr Blonder said.
In addition to the leaves’ mass-per-area ratio, the scientists measured the density of the leaves’ vein networks.
“By comparing the two parameters, we get an idea of resources invested versus resources returned, and that allows us to capture the ecological strategy of the plants we studied long after they went extinct.”
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Blonder B et al. 2014. Plant Ecological Strategies Shift Across the Cretaceous–Paleogene Boundary. PLoS Biol 12 (9): e1001949; doi: 10.1371/journal.pbio.1001949
