Methane production

["Richard W. Travsky" <rtravsky@uwyo.edu>]

http://www.newscientist.com/article/mg20627623.300-did-early-hunters-cause-climate-change.html

When hunters arrived in North America and drove mammoths and other large 
mammals to extinction, the methane balance of the atmosphere could have 
changed as a result, triggering the global cool spell that followed. The 
large grazing animals would have produced copious amounts of methane, a 
potent greenhouse gas, from their digestive systems. 
[...]


Just out of morbid curiousity, what would the methane production numbers 
work out to be for all those dinos?