Stupid Dinosaurs. Wiped themselves out burning fossil fuels, only to become fossils themselves.
Unless I'm mistaken, 300 million years ago was well before the age of Dinosaurs––in the Paleozoic.
As for an increase in CO2 during this time, how are these estimates being produced?
There are no ice cores from that era to trap 300 million year old bubble of air so the only thing I can imagine is they are somehow inferring atmosphere from sedimentary rock.
P.S. As for Dinosaurs and global warming, it is now believed that the quality of plant food made fermentation (a tactic used by cows––some of which can sustain a flame) a common necessity to extract value from low-quality plants. As fermentation gains efficiency as scale increases, a big stomach means a big, hungry dinosaur.
But pray tell imagine a 35 to 60 ton cow?
The sheer quantity of fart gas (methane) would have been staggering and such is considered a component of global warming. Add in the termites and more oxygen in the atmosphere and it's easy to see how there could be herd die offs––one lightning strike at the wrong time/place and instant firestorm.