I would just like to add a word about similarity of form. In the world there are just so many shapes.
Every culture has a fascination and deep seated mythologies about birds. They are often used as motifs in
all of these cultures and when stylized the similarities become even stronger. As a trained percussionist i have often marveled at the similarities between the ritual rhythms of various cultures spread all across the globe. I was recently noting a rhythm in some Indonesian music that sounds very much like one i know that originated in the Congo. There are, infact, root rhythms that transcend all cultures. This is not because these cultures have had contact with each other. It is merely the nature of things.
Someone just recently pointed out the pyamid at Candi Sukuh in Jawa to me. Let us compare it to the Mayan temple of Chichen Izza. So what do you think Baganing. Did the Mayans make their way to Jawa in the 15th century and influence the temple form at Candi Sukuh.

....of course, there is always my old favorite, the aliens from space theory...