- Insect numbers and sizes were growing through most of Earth's history until the bird arrived.
- Bird's ability to snatch insects from the air forced them to evolve smaller, more maneuverable bodies.
Giant insects that ruled prehistoric skies for millions of years may have met their end due to the evolution of predatory birds, researchers say.
Gigantic insects once dominated the Earth. About 300 million years ago, during the late Carboniferous and early Permian periods, the largest flying insects known, the predatory dragonfly-like griffinflies, had wingspans of up to 28 inches, about the same as the modern wood duck.
The leading theory of how flying insects reached such stupendous sizes has to do with past periods of high oxygen concentrations in the atmosphere, reaching up to some 50 percent richer than today. All this extra oxygen is thought to have supported the energy-hungry metabolisms of flying insects, helping them grow to titanic maximum sizes.
To test this theory linking oxygen with body size, paleontologists Matthew Clapham and Jered Kerr at the University of California, Santa Cruz, compiled a data set of insect wing lengths from more than 10,500 fossils collected from more than 1,000 published records. They next compared wing sizes with models of prehistoric atmospheric oxygen levels from data spanning the last 320 million years.