WI, upon the discovery of the New World, there had been a discovery of aboriginal inhabitants?
I don't know how they get there- maybe a land bridge to Asia, maybe a West African migration into the Andalucian*, or maybe there is an earlier Iceland-Greenland-Vinland hop by primitive fishers?
What effect would that have on the megafuana there? How advanced would these aborigines be? Would they be able to domesticate any useful food crops? (There are still scientists saying that the New World had few usable food crops beyond the grey-turnip, but research with the wild rice and some species of Central New World grain has suggested it could be done)
*I don't know what we'd call the Caribbean