One day, about 60 million years ago, a little leafcutter moth landed on an ancient sycamore tree to lay eggs in its leaves. The larvae grew, nestled inside a comfy enclosure akin to a sleeping bag made between the leaf’s thin layers. Once hatched, they ate their way through to the surface and left to perpetuate their kin. Most of the chewed-up leaves swirled down to the earth, decomposing shortly after.
But this leaf, along with a few lucky others, was destined for something else, an unimaginable feat verging on immortality. When it fell, this leaf either sank deep into mud or was swept away by a flooding river that buried it within the sediment layers. There, tucked away from oxygen and the bacteria that would’ve finished what the larvae did not, it survived for millennia, becoming fossilized. It lay there, tucked into the bedrock of obscurity, until one day scientist Lauren Azevedo-Schmidt, who was working on unearthing such relics, spotted it on a fossil bed in Southern Wyoming.
Azevedo-Schmidt pried the leaf out of the rock with a paleo pick and chiseled it out of the stone slab. In her lab at the University of Wyoming where she was working on her Ph.D., she put the fossilized leaf under a microscope and examined the remains of the prehistoric larvae’s handiwork, noting the damage done—the round, hole-like pockets in which the creatures had lived. Then she added the sample to the existing collection of chewed-up and scratched-up ancient leaves, which by the end of her doctoral work amounted to a veritable forest: 77,763 specimens.
Within this “stone forest,” Azevedo-Schmidt and her supervisor, paleoecologist Ellen D. Currano, documented different types of leaf damage—a concept they describe as “damage diversity.” They found seven types of miniature decimation, from holes to galls to piercings. Then they compared the leaf damage done by the prehistoric insects to the destruction made by the creatures of our era. The results flew in the face of what they expected.
They found that compared to the insects from the late Cretaceous period—about 67 million years ago—modern bugs are doing an unprecedented amount of damage to plants. The more recent leaves, handpicked from modern woods and in existing herbariums—the Smithsonian Environmental Research Center in Maryland, Harvard Forest in Petersham, Massachusetts, and Le Salva in Costa Rica—were more chewed up, pierced, and misshapen that those from eons ago.
Compared to prehistoric leaves, modern ones also tended to be mangled in more ways. They had a greater “damage frequency” as well—which meant that there were many more chewed up and misshapen leaves in the recent samples than in the ancient ones. This pattern intensified in the past century, hinting that the industrial revolution played a role. [Continue reading…]