Giant Dragonflies With 2-Foot Wingspans Ruled the Skies 300 Million Years Ago -- But Oxygen May Not Explain Why(Discover)

[eppur_se_muova]

Written byAnastasia Scott

Mar 25, 2026, 4:50 PM | 3 min read

Before birds or bats took flight, the skies were filled with insects, and some of them were enormous. Around 300 million years ago, dragonfly-like creatures with wingspans reaching 27 inches (70 centimeters) — nearly the width of a modern hawk — flew above swampy forests. These “griffinflies” lived in a world shaped by coal swamps, frequent wildfires, and much higher oxygen levels than today.

Those elevated oxygen levels have long been thought to explain how insects reached such massive sizes. But new research, published in Nature, is challenging that idea, suggesting these giants may not have depended on oxygen as much as researchers once believed.
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That idea began to take shape in the 1980s, when new techniques allowed geochemists to reconstruct the composition of ancient atmospheres. Their findings showed that oxygen levels were significantly higher around 300 million years ago — about 45 percent higher than today.

In the 1990s, researchers connected those elevated oxygen levels to fossil evidence of giant insects, proposing that larger bodies would require more oxygen to fuel flight. The timing lined up, and the idea quickly became the leading explanation for why insects once reached such massive sizes.
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more: https://www.discovermagazine.com/giant-dragonflies-with-2-foot-wingspans-ruled-the-skies-300-million-years-ago-but-oxygen-may-not-explain-why-48866

[rampartd]

1. good article at discover

if the limit in insect size is not oxygen .....

there was a late carboniferous ice age. more compact bodies conserve heat....