As the first birds took to the skies about 150 million years ago, huge insects started to decline, say scientists.
Millions of years ago, oversized insects like griffinflies boasting wingspans comparable to today's hawks scuttled across (and fluttered above) the planet. But why these jumbo jets of the insect world shrunk to modern size has remained a mystery, until now.
Turns out, as dinosaurs evolved flight and eventually took to the skies as birds, they beat down the huge insects already living there, effectively putting a cap on insect size through predation and competition in the prehistoric skies, as birds developed into sophisticated flying machines.
"The change in insect size is gradual," study researcher Matthew Clapham, of the University of California, at Santa Cruz, told LiveScience. "This gradual change fits quite nicely with the gradual evolution in birds at the time."
Insects during the Permian era (about 290 million to 250 million years ago) were huge compared with their counterparts today, boasting wingspans up to 30 inches (70 centimeters) across. The high levels of oxygen in the prehistoric atmosphere helped fuel their growth.
For comparison, the biggest modern winged insect is a dragonfly from the tropics, which has a wingspan of about 8 inches (20 centimeters) across. [Dazzling Photos of Dew-Covered Insects]