In this Native American History class that I'm taking, we talked a bit about different population stories and creation myths for different tribes. It was really interesting. The Leni-Lenape tribe (I think they were from the present day Maryland area?), have a story about a woman who was the "first woman", I guess, and she was dropped from a giant bird onto her people's land. Interestingly, in a few images that we saw from tribal artists depicting this scene, their land (which to early tribes was the entire earth) is said to rest on the back of a tortoise floating in a universal ocean.
I thought about Kurma and wished I could recall the story of this avatar. It's this (and other) stories that I hear that make me wonder if the idea of centralized "first culture" that spread out all over the world is really that far off.
"ksitir iha vipulatare tisthati tava prste
dharani-dharana-kina-cakra-garisthe
kesava dhrta-kurma-sarira jaya jagadisa hare"
O Kesava! O Lord of the universe! O Lord Hari, who have assumed the form of a tortoise! All glories to You! In this incarnation as a divine tortoise the great Mandara Mountain rests upon Your gigantic back as a pivot for churning the ocean of milk. From holding up the huge mountain a large scar like depression is put in Your back, which has become most glorious.