Here is Michael Bay's response to us TMNT fans that got pissed off when he said they will be from an alien race.
Fans need to take a breath, and chill. They have not read the script. Our team is working closely with one of the original creators of Ninja Turtles to help expand and give a more complex back story. Relax, we are including everything that made you become fans in the first place. We are just building a richer world.
here is my source