[aruanan]

Since insects are limited in size by their respiratory system, not their weight, and these six times larger insects have NO [structural] adaptation for their larger size, whatever was different about their environmental conditions had to increase the efficiency of their respiration.

Insect respiration is basically a tube from the outside of the body that reaches down to within each couple of cells. If there was a higher percentage of oxygen in the atmosphere, that could support a larger overall form.

[zot]

Insect respiration is basically a tube from the outside of the body that reaches down to within each couple of cells. If there was a higher percentage of oxygen in the atmosphere, that could support a larger overall form.

Yes, that was the point I was suggesting. And I think that a higher percentage of oxygen in the atmosphere would also facilitate larger life forms in species other than insects, by providing more efficient respiration and thus more energy to overcome the weight of their larger size.

It also occurs to me that the percentage of oxygen in the atmosphere may have been significantly reduced by the massive fires caused the impact about 65 million years ago.