As I pointed out in the post you responded to the fossil found had teeth. That means it had a different way of feeding itself than the platypus, therefore there are differences for sure between this creature and the platypus we know and love because the platypus is extremely well equipped for the way he lives and eats. What these differences are though, we cannot tell. A pile of bones (and in this case just the head) cannot answer the question posed to you: what exact animal has the traits from which the peculiar traits of the platypus descended. Obduron does not answer the question.
To recapitulate, the platypus has traits only seen in species as far apart evolutionally as snakes, mammals, fish and birds. Which did it come from? How did all those traits develop graudally in an evolutionary way? That is the question and that is the answer you cannot give.
The skull is reported as "more generalized." That means "less specialized." That means "not yet fully a platypus." It's a transitional. That's what you wanted, right? (WRONG!)