By: Jennifer Welsh, LiveScience Staff Writer
Published: 06/04/2012 03:13 PM EDT on LiveScience
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]
To figure out why modern insects are no longer so big, the researchers compiled a database of wingspan measurements of 10,500 fossilized insects from the last 320 million years of insect evolution. The authors found that during the first 150 million years of insect evolution, the wingspans on these insects mirrored levels of atmospheric oxygen; the more oxygen in the atmosphere, the larger the insects the environment could support.
These flying insects need lots of oxygen to support their flight muscles, Clapham said, and since their breathing tubes are inefficient, they need high atmospheric oxygen levels to grow large. The more oxygen in the environment, the more muscle mass the insect can provide oxygen for and the larger the insect can be.
Around 140 million years ago, though, things changed. Insect wingspan stopped depending on oxygen levels and started dropping.
The researchers noticed that this change happened around the same time that birds first took to the skies. About 150 million years ago, the "first bird" Archaeopetryx appeared, and about 25 million years later, the lineage had diversified greatly.
Over time, the birds developed physical features that enabled quick flying and better maneuvering. As a result, they started eating the large insects, and competing with them for food sources.
"These large insects are predatory, and they eat smaller insects. It's possible that birds may have also eaten small insects, as many modern birds do," Clapham said. "If they are competing for the same resourse, birds may have been better competitors for these food sources."
A second slump in insect size happened about 60 million years ago, which the researchers think could be related to the evolution of bats, further increases in birds' aerial abilities, or to the mass extinction event that killed the dinosaurs.
The study is detailed today, June 4, in the journal Proceedings of the National Academy of Sciences.
You can follow LiveScience staff writer Jennifer Welsh on Twitter, on Google+ or on Facebook. Follow LiveScience for the latest in science news and discoveries on Twitter and on Facebook.
Copyright 2012 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Our 2024 Coverage Needs You
It's Another Trump-Biden Showdown — And We Need Your Help
The Future Of Democracy Is At Stake
Our 2024 Coverage Needs You
Your Loyalty Means The World To Us
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
The 2024 election is heating up, and women's rights, health care, voting rights, and the very future of democracy are all at stake. Donald Trump will face Joe Biden in the most consequential vote of our time. And HuffPost will be there, covering every twist and turn. America's future hangs in the balance. Would you consider contributing to support our journalism and keep it free for all during this critical season?
HuffPost believes news should be accessible to everyone, regardless of their ability to pay for it. We rely on readers like you to help fund our work. Any contribution you can make — even as little as $2 — goes directly toward supporting the impactful journalism that we will continue to produce this year. Thank you for being part of our story.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
It's official: Donald Trump will face Joe Biden this fall in the presidential election. As we face the most consequential presidential election of our time, HuffPost is committed to bringing you up-to-date, accurate news about the 2024 race. While other outlets have retreated behind paywalls, you can trust our news will stay free.
But we can't do it without your help. Reader funding is one of the key ways we support our newsroom. Would you consider making a donation to help fund our news during this critical time? Your contributions are vital to supporting a free press.
Contribute as little as $2 to keep our journalism free and accessible to all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
As Americans head to the polls in 2024, the very future of our country is at stake. At HuffPost, we believe that a free press is critical to creating well-informed voters. That's why our journalism is free for everyone, even though other newsrooms retreat behind expensive paywalls.
Our journalists will continue to cover the twists and turns during this historic presidential election. With your help, we'll bring you hard-hitting investigations, well-researched analysis and timely takes you can't find elsewhere. Reporting in this current political climate is a responsibility we do not take lightly, and we thank you for your support.
Contribute as little as $2 to keep our news free for all.
Can't afford to donate? Support HuffPost by creating a free account and log in while you read.
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. Would you consider becoming a regular HuffPost contributor?
Dear HuffPost Reader
Thank you for your past contribution to HuffPost. We are sincerely grateful for readers like you who help us ensure that we can keep our journalism free for everyone.
The stakes are high this year, and our 2024 coverage could use continued support. If circumstances have changed since you last contributed, we hope you'll consider contributing to HuffPost once more.
Support HuffPostAlready contributed? Log in to hide these messages.