Truth about the Molossus Dog?

I've been looking into the history of Mastiffs. I own a 4 month old English Mastiff and I was just curious. After reading the information provided by the AKC, I found some researchers who disagree with the standard history of what the Molossus dog was and if it indeed was an ancestor of the Mastiff and the dog depicted in Assyrian drawings. Just wondering if anyone has any trust worthy websites with solid scientific facts?