[Andrew Askew]

Andrew Askew asked the Naked Scientists:
   
Is the content of oxygen in the air a limiting factor in the maximum size of land based animals? Was the air oxygen rich during the reign of the dinosaurs partially explaining the immense size of the sauropods (amongst others)?

Love the podcasts by the way. I have just started trying to catch up from 2005!!!!!

What do you think?

[RD]

The Jurassic period was warmer and had higher levels of carbon dioxide than today, so more vegetation => bigger herbivores possible.

(There was more oxygen too: oxygen is the waste product of plants)

[RD]

The biggest animal that has ever lived is alive today: the blue whale, despite our current lower concentration of atmospheric of oxygen than in the Jurassic period.

... Interestingly, there is no significant correlation between atmospheric oxygen and maximum body size elsewhere in the geological record.

http://en.wikipedia.org/wiki/Geological_history_of_oxygen

[Nizzle]

Higher concentration of oxygen would allow an increase of size in creatures that use oxygen in a poor manner, ie insects.
There was an era before the dinosaurs, where oxygen levels were 40% higher than today, and in this era, insects (or more accurate arthropods) could grow to sizes you would nowadays only see in horror flicks.