Experiments on modern plants show that the nutrients which dinosaurs could get from plants varied with carbon dioxide levels
Our fascination with giant sauropod dinosaurs such as Diplodocus, Brachiosaurus and Brontosaurus stems from their colossal size. How could something 30 metres long, weighing 50 tonnes, function as a land animal? And how could something that big gain enough nutrition from plants?
We have little evidence for the diet of everyone’s favourite giant herbivores. Reports of fossilised stomach and gut contents have been contested, and coprolites (fossilised dung) are difficult to assign to their producer with any certainty. Indirect evidence from comparative morphology with giraffes and elephants, the largest modern analogues, suggests that sauropods would browse from the tree canopy, although researchers disagree about whether all sauropods held their heads high. Some have even suggested niche partitioning between the different sauropod groups, with the tallest brachiosaurs feeding from the top of the canopy, camerasaurs in the mid-canopy, feeding on seed-ferns and cycads, and diplodocids grazing on ferns and horsetails at ground level.