When a 10-kilometer-wide object slammed into Earth about 66 million years ago, it created an ecological catastrophe. In the ensuing environmental chaos, dinosaurs died out but mammals survived, setting the stage for the modern world. Now, scientists have confirmed that the plant kingdom suffered similar disparities after the impact, losing many more flowering evergreen species than plants that drop their leaves each year. Researchers looked at more than 1000 fossilized leaves from rocks deposited in what is now southern North Dakota during a 2.2-million-year interval spanning the dino-killing impact. In the 1.4 million years prior to the impact, leaves from the various species of flowering plants in the ecosystem had, on average, thicker and heavier leaves with fewer veins than those that lived in the 800,000 years after the impact, the researchers report online today in PLOS Biology. Thin, veiny leaves are a signature of deciduous plants; even though such leaves must be replaced every year, they allow deciduous species to take up carbon more quickly than their evergreen cousins. This "live fast, die young" strategy enabled deciduous survivors to better take advantage of the extremely variable postimpact climate in which suitable conditions for growth—especially those steady conditions generally preferred by slow-growing evergreens—occurred less frequently, the researchers propose. They conclude that postapocalyptic forests were likely chock-full of fast-growing deciduous species such as extinct relatives of sycamores, walnuts, and palms (pictured above in an artist's reconstruction), whereas thick-leaved, slow-growing evergreens similar to today's hollies and ivies were much less common than they had been prior to the impact. Even today, the researchers note, few if any forests are dominated by flowering evergreens.









