MonsignorJabroni t1_jaje9hk wrote on March 1, 2023 at 9:21 PM

Reply to comment by Thunderhamz in Giant Jurassic-era insect rediscovered outside Walmart in Arkansas by Hamsternoir

It is well known and established that insects and other creatures were larger during dinosaur times because there was more oxygen in the atmosphere, amongst other things. Pretty much everything was bigger because it could absorb more oxygen and nutrients from the environment.

Human or proto human sizes have changed but we're taking like 100k years for humans, not 300 million years ago. As far as earth history is concerned, humans haven't been around long at all and haven't seen much change. Obviously we see change, but mother earth time is a different beast.

palcatraz t1_jajjp1l wrote on March 1, 2023 at 9:55 PM

That's not exactly correct.

Only insect size correlates to oxygen content in the air due to the manner in which they breathe. However, oxygen content is not the only limiting factor in size. The Carboniferous and early Permian are when insects sizes maxed out. This is before the age of the Dinosaurs (who didn't start appearing until the late Triassic). Up to this point, insect sizes and oxygen content in the air is well correlated.

This changes during the Jurassic. Insect sizes dropped after the Permian when the oxygen content in the air dropped low. However, even when the oxygen content in the air started increasing again, insect sizes continued to diminish in size. Reason? Birds had started to evolve. With birds now dominating the air, and in many cases, preying on insects, being large no longer held the same advantages as it once did.

And again, this is just for insects. Other terrestial animals, such as dinosaurs or mammals were never limited in size by oxygen content. That's because we have a far more efficient way of breathing than insects do.

MonsignorJabroni t1_jajm4ob wrote on March 1, 2023 at 10:10 PM

Thanks for correcting me, I wasn't sure on the specifics, I knew it was related to oxygen in a way. I appreciate the explanation that's really interesting.

I guess I was just a little amused by the implication of Giant Humans or something from the initial comment lol. Like no, we weren't 10 feet tall humans years ago, I'm pretty sure that's confirmed.