As mentioned on that Wikipedia page, that big dragonfly-like insect from the upper Permian was already only slightly more than half the size of its ancestors fr

As mentioned on that Wikipedia page, that big dragonfly-like insect from the upper Permian was already only slightly more than half the size of its ancestors from the lower Permian, which could have been caused by the lower oxygen content in the air. The fact that it was still much larger than current insects is most likely explained by the fact that there were no flying vertebrates that could compete with it or hunt it.