At https://phys.org/news/2026-03-massive-insect-body-size-million.html … 300 million years ago Earth was quite different. The continents had coalesced into Pangea and there were high oxygen levels. Water teemed with fish and on land amphibians, reptiles, and crawling anthropods, as well as giant cockroaches, ruled the roost. In the air there were flying insects – some of which were massive in size. These included may flies with 17 inch wing spans and enormous dragon flies with 27 inch wing spans. They were discovered in fine grained sedimentary rocks in Kansas.
It was speculated, and became the acceptable consensus, the giant dragon flies could only exist because of atmospheric oxygen levels much higher than in the modern world. In the 1980s, geochemists claimed to be able to reconstruct the gas composition of past atmospheres. The striking discovery was the high oxygen levels 300 million years ago. When it was pointed out this coincided with the period of the giant insects it was proposed they required a higher demand for oxygen to achieve larger body size. Insects, it was found, obtain oxygen via a trackeal system – a branching tree like arrangement of airways leading to the tracheoles. Hence, oxygen must move down concentration gradients to the trackeoles in order to fuel the flight muscle cells. It was assumed that large insects could not survive nowadays because oxygen levels in the atmosphere are too low. However, a study in Nature journal [see https://doi.org/10.1038/s41586-026-10291-3 …] using electron microscopy, found the space occupied by trackeoles in a percentage view is similar to today’s insects. This indicates flight muscles of insects are not constrained by atmospheric oxygen levels as they could easily add trackeoles in the muscle if necessary. In an evolutionary manner. In other words, the giant dragon flies were really just that – giant forms of modern dragon flies. The final paragraph reads – ‘if oxygen does not limit maximal insect size, then other culprits are responsible for the modern small size of insects.’ It occurred to me that if sedimentary rocks were laid down quickly during catastrophic events of one kind or another and then the high oxygen levels displayed 300 million years ago may actually have been caused by the catastrophic event itself. The normal periods in between catastrophic events may not display high oxygen levels – but we don’t know that as they have not been preserved in the fossil record. There must be another reason for the large size of insects back then.