Very nice homage to Aboriginal art. But it seems more like a stand-alone piece, not a shirt design. As I look at the overall composition, it seems rather unfinished (as a t-shirt design). The lizard is just kind of floating in space, at an angle that may not wear well on a person, given their sex or build.
You could add some additional nebulous dot art leading and/or trailing the lizard (the grey foot print elements). Or change the lizard's body position entirely, make it climb more vertically down one side of the shirt, or across the chest area.
There just seems to be something missing (again, as a t-shirt design).