DOWN UNDER KNOWLEDGE TEST.

I grow to a length of around 70cm, I have 4 legs, a scaly body, can change from light gray to dark gray for camouflage, can run at considerable speed on my two back legs, have a large brightly coloured mouth, hiss when frightened, have fan shaped loose neck skin I extend when defending myself. I lay up to 40 eggs per season. My main diet is ants, other insects like casidas and small lizards. I have also featured on Australian coins………
what is my name?

ANSWER