Atmospheric changes

Atmospheric changes
I watched various discover channel shows recently. Someone commented on the size of plants and animals. It was unknown why everything was so big in the fossil record. The largest dragon flies now are about 20 centimeters. The largest in fossil record are 75 centimeters. That is more than 3 times increase in size. I don’t know anything about the behavior of the old dragonflies but assuming they are similar to dragonflies we see now they flew and hunted prey. That requires some speed and agility. Their bodies appear similar. If their flight patterns were the same and body construction was the same then it should require a different environment to allow the larger size. I wouldn’t expect a 75 centimeter dragonfly to be able to turn or sprint like a smaller dragonfly. Mass to lift ratios don’t match. Nature’s design appears to limit size. Although bird construction is very light there is a limit to the size of birds. Condors and vultures are the largest. I remember the old nature shows which would show these birds struggling to take flight after eating because they had reached their weight limit. Yet these are dwarfed by flying dinosaurs called pteranodons or pterasaurs. Some of these had wingspans of more than 35 feet. Again more than 3 times what we have today. Scientists agree that the designs could glide but debate about how they would have become airborne.

My guess is that the atmosphere was 3 times as dense as it is today. There must have been changes in the atmosphere. The size of dragonflies should be optimized for prey and environment. They would not have grown so large if flight was hindered. Fossils don’t seem to show structural differences to decrease weight or improve flight. The air must have been thicker to allow lift/buoyancy required.

I thought about it and did a search and found that some people have put a lot more effort into this.
http://www.levenspiel.com/octave/dinosaur1.htm