I have this as an illustration in a Peter Colosimo "Gods From Outer Space" book but I think it came originally from a magazine such as ARGOSY in the 1970s. And actually while the skulls are unusual in the Amazon basin, they are not unidentifiable. As a matter of fact they resemble two basic types of Megalith-builders from Western Europe and can be looked upon as ultimately like the CroMagnon and Combe-Capelle Ice age "Cave Men." And you have living people in the Iberian peninsula that are much like them today. The problem is, are they recent or ancient Iberians in that case? They COULD be nothing more than Portugese colonials that met an untimely end, or they COULD have been shipwrecked on a Phoenician galley. Without testing the skulls themselves there might not be any way of telling. And below is a newspaper article on a giant skull found in Texas. It is once again unusually large but conforms to the ADENA type. I have heightened the contrast on the photo at the bottom.

http://frontiers-of-anthropology.blogspot.com/2012/01/more-skulls-trepanned-indus-mayan.html