Is it possible that increased CO2 levels during the larger dinosaurs era is a major factor in why dinosaurs grew so big during this period?

And extrapolating this question, is it possible that the increased CO2 during the industrial revolution has contributed to each generation of man growing bigger?

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    $\begingroup$ what would be the mechanism for CO2 (carbon dioxide) levels making dinosaurs bigger? I'm missing some detail to your question. Yes, higher O2 (oxygen) levels are linked to larger animal sizes. But I've never heard of a link to CO2. $\endgroup$
    – Erik
    Nov 11 at 7:00
  • $\begingroup$ Regarding the second question, what has enabled humans to grow taller is improved nutrition and health, particularly in the first two years of ones life. For example, North Koreans are measurably shorter than are South Koreans, mostly because of extreme poverty in North Korea vs lack thereof in South Korea. $\endgroup$ Nov 12 at 0:05
  • $\begingroup$ Why Dinosaurs Were So Big discusses four theories and says it is still debated. $\endgroup$ Nov 23 at 19:18

The reason why humans are growing bigger (excluding any fat jokes) is because bigger humans must eat better, thus are more capable of surviving, and are also much better fighters (better strength/reach). This led to size being considered a favorable trait, leading humans to select larger mates and thus evolve to be larger. Once we started dominating the environment, we all grew larger, but the same instinct persists even today (just ask any guy under 6 feet).

As for the dinosaurs, there was much more oxygen and CO2 in the atmosphere, so plants had more soil to grow in, the earth was hotter so more precipitation occurred, causing massive rainforests, and most importantly there was lots of O2/CO2 to breathe (plants breathe CO2, which gives them the majority of their mass).

Over millions of years this C/O was sequestered underground, and things evolved to be smaller to compete as the earth starved of life-giving Oxygen and Carbon. Now we are putting it back in circulation, reversing this trend. However, this reversal causes changes, and as change is scary it is by default bad.


Climate made the dinosaurs big. Studies of air bubbles trapped in various samples of amber show that the atmosphere of the Cretaceous may have had up to 35 per cent oxygen, compared to only about 21% today. Dinosaurs first appeared during the Triassic when there was lower oxygen so early dinosaurs were small; therefore developed highly efficiency breathing that allowed them to survive. All the while many species became extinct. The Triassic-Jurassic extinction event killed more than half the species, including several mammals and mammal-like reptiles (Synapsids) but allowed new dinosaurs of filling niche. CO2 levels were in the 1000-2000 ppm ratio so it fed a Huge ecosystem of vegetation. CLimate was relatively warm, so much so metabolism was devoted to growth than temperature moderation.

  • $\begingroup$ Dinosaur gigantism has not ben fully understood as yet and agree "Darwin evolution is the key" and i thought increased Co2 levels during this period might be a driving factor for gigantism. that idea also got me thinking that each generation of mankind has also got bigger statistically. yes I agree better nutrition etc but i found it interesting that during the industrial revolution Co2 levels have also increased - making me think about Co2 somehow being a contributing factor to size growth in animals. Not being a scientist, I was looking for a link between Co2 and growth in animals $\endgroup$
    – rhett
    Nov 12 at 14:49

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