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User avatar #36 - jalthelas
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(05/07/2013) [-]
The theory is that there was a lot more oxygen in the atmosphere back during the age of the dinosaurs, which allowed mammals, reptiles, and other species to grow much larger. They are not able to grow to such sizes today with the lesser amount of oxygen in the atmosphere.
User avatar #62 to #36 - xxechoesxx
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(05/07/2013) [-]
I also had heard that. sounds plausible & would account for such unique spices.
User avatar #52 to #36 - KiraLives
Reply +1 123456789123345869
(05/07/2013) [-]
Actually oxygen was only about 50% higher back then, at it's highest, and lower than today at it's lowest (as a side note, CO2 was about 600% higher), it may have contributed to their massive size, but it wasn't the main reason. Dinosaurs had bird lungs (or more properly, birds have dinosaur lungs), so they were extremely efficient at getting oxygen out of the air. The Mesozoic was also a warm period, which helps increase animal diversity. Size is a good strategy, if you're too big to eat, you won't get eaten, and if you don't get eaten, you make more babies. It works the same way with carnivores, the bigger your food is, the bigger you have to be to take it down, unless you change strategies and try pack hunting (or eating plants, therizinosaurus I'm looking at you). Mammals have gotten huge before too, and that happened without significant boosts in oxygen.

Also, in reference to your comment below, the giant dragonflies are from the Carboniferous period, which is long before the dinosaurs first appeared.

I'm studying to be a paleontologist, if you guys have any further questions!
#42 to #36 - KungFuZerO
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(05/07/2013) [-]
I've heard that too. Pretty awesome if its true. Massive animals due to increased oxygen levels. Who woulda guessed?
#37 to #36 - dsmb
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User avatar #38 to #37 - jalthelas
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(05/07/2013) [-]
Yep, it explains the fossils of giant dragonflies and other insects.

Truly would be terrifying to see giant spiders, centipedes, and others.