In American Gods Gaiman tells a brief interlude where a group of native Asian peoples are crossing the land bridge through the Bering Straight to become the native American peoples. They bring with them the skull of a mastadon that was their god. When they reach the new world, their god was no longer necessary to them as they found other animal totems to worship in the Americas. The skull is left somewhere in the Aleutians.

So, for my game, that skull wasn't their god, but rather an enchanted skull that could ward of shedim spirits. The times of the real world don't quite coinside with the way I'd like things to work out so things in My World ™ will just be different. So now that the shedim have re-entered the world, they're trying to move on the artifacts that helped keep metahumanity safe last time. If they can succeed, they'll be able to cause havok and strife and all the things that shedim like to do.

The mastadon skull no longer is necessary because in Gaiman's North America, the land itself is the only God that will exist without fighting tooth and nail for it, not that there were other animal gods.