This is a big issue it would seem. There are 24 articles on megafauna in January's Ecography journal and the journal of PNAS – see http://phys.org/print373189841.html
They are based on a conference that took place at Oxford University back in March of 2014 (only now being written up in journal form and published). We don't learn much about the contents from the press release, only that we are supposed to be living in the shadow of big beasts that were once in abundance on all the continents of the earth.