Nope. The oxygen ratio in the atmosphere varied and included long periods with comparable levels as today.
The most important part was their biology, that helped move the oxygen around the bodies of the massive giants. Remember that while there were massive giants, the blue whale is the largest animal ever known and they live today alongside dolphins and otters just like how dinosaurs came in a wide variety of sizes all living at the same time.
Nope. The oxygen ratio in the atmosphere varied and included long periods with comparable levels as today.
The most important part was their biology, that helped move the oxygen around the bodies of the massive giants. Remember that while there were massive giants, the blue whale is the largest animal ever known and they live today alongside dolphins and otters just like how dinosaurs came in a wide variety of sizes all living at the same time.