Did you know that there is a bullhead shark mimics the appearance of the Port Jackson shark? The crested bullhead shark is virtually (compared to other bullhead sharks) its twin – with slightly larger ridges above the eyes, slightly lighter and different markings and tendrils on its egg cases.
It is a coincidence that the crested bullhead is one of the major predator of the eggs of the Port Jackson shark? I don’t think so. If you want to steal an egg case under the nose of its mother it is convenient to look like a female Port Jackson intend to put your own egg into a crevice. And if you have the egg case in your mouth you can crack it to get at the yolk.