How many dinosaurs roamed the earth at their maximum? For instance, nowadays, you could say, well there’s about 100,000 aligators in the world, or 200,000 buffalo. So how many T-rexes, Brontosauruses, etc. were there at their peak in numbers?
Thanks!
Scott
This question is currently inpossible to answer with any reasonable degree of accuracy. We have discovered only a small fraction of the fossil record. There are esimates of herd sizes being as large as 10,000 but herds these are probably mixed herds.
You can probably narrow your search down to the Cretaceous period since that’s generally accepted as the time when dinosaurs were the most numerous 
You might be interested in the dinosaur mailing list archives, available at:
http://www.cmnh.org/dinoarch/ .
I’ll bet I can guess the number of Brontosauruses alive at any given time. 