U.S. scientists have found that the evolution of birds may have triggered the extinction of gigantic insects, according to a report on Proceedings of the National Academy of Sciences.

Researchers from the University of California, Santa Cruz studied the fossil records dating back to Carboniferous period, and found that high oxygen levels of the time allowed species like dragonfly-like Meganisoptera to have wingspans of up to 71 centimeters around 300 million years ago. Further study showed that maximum insect size changed over time in proportion to oxygen levels.

But around 150 million years ago, insects started to get smaller despite rising oxygen levels.

Scientists are suspecting that this is due to evolution of predatory birds during the time. In order to evade the birds that were becoming more mobile, the insects needed to slim down.

However, this theory does not fully explain the fact that pterosaurs, which lived around 230 million years ago, did not affect the size of insects, although this may have been because the flying reptiles are suspected to have been less mobile than most birds.

Also, other factors like a 20-million-year gap in fossil records, lack of variation in insect sizes – larger insects are much more likely to be preserved – and evolution of other possible predators like bats makes it hard for researchers to definitively announce the correlation between the emergence of birds and disappearance of giant insects.


By Yoon Min-sik
(minsikyoon@heralm.com)