According to the researchers, giant insects that ruled prehistoric skies for millions of years may have met their doomsday due to the evolution of predatory birds.
Researchers further stated that the struggle ended an era of insect growth spurts that coincided with abundance in the amount of oxygen level in the air. Starting with the Cretaceous period, predators kept the sizes of insects down.
“That’s when birds evolved and started to become better at flying,” says Matthew Clapham, a paleontologist at the University of California, Santa Cruz. “Even though oxygen continued to increase during that time, the insects got smaller.”
Its been widely acknowledged that oxygen can boost growth. Beetles and dragonflies that breathe oxygen-enriched air tend to grow bigger. Its believed to be a universal fuel that boosts the metabolism of any insect.
To work out oxygen’s effects on prehistoric insects, Clapham and Santa Cruz colleague Jered Karr examined more than 10,500 fossil specimens from the last 320 million years. The researchers compared changes in maximum size over time to changes in atmospheric oxygen, as reconstructed from ancient sediments.
“There’s been a lot of theories about body size and oxygen, but the problem has been not having enough fossils to actually test some these theories,” says Wilco Verberk, an ecologist who studies insect physiology at Plymouth University in England. “This is the most comprehensive dataset gathered to date.”
Small insects were omnipresent throughout the record. But the biggest of the big insects enlarged when oxygen levels rose and shrank when oxygen levels fell. About 300 million years ago, dragonflies sported wings comparable in size to those of a modern duck. At the time, oxygen made up more than 30 percent of the atmosphere as compared to about 21 percent today.
One interpretation for the insects’ failure to regain their former glory can be due to the beginning of the aerial revolution. Creatures like Archaeopteryx gave way to birds with greater flexibility. Upgraded body plans featured smaller tails, specialized wing bones and giant breastbones.
Clapham deduces that the winged newcomers gorged on the over-sized bugs. But it’s also possible that both types of large predators fed on the same small insects, and birds simply proved to be the better hunters.
The study was reported online on June 4 in the Proceedings of the National Academy of Sciences.