This is, of course, the Australian frilled lizard Chlamydosaurus kingii, so called because of the large ruff of skin that usually lies folded back against its head and neck.
The frill is used in territorial and sexual displays, and is supported by long spines of cartilage. When the lizard is frightened, it gapes its mouth, showing a bright pink or yellow lining, and the frill flares out, displaying bright orange and red scales. The frill may also aid in thermoregulation.
Now, here's a question for you. What other use, allegedly, is the frill used for? If you want to make a guess, please post your ideas here, and I'll give the answer on Sunday...
Have a great weekend!