How did the new species come into being since the flood?
The genetic material for all present species, except for those not needed or desired prior to the world wide deluge, would be sufficient in those creatures aboard the ark to generate such diversity.
If one cares to take things down to the level of basic elements,everything has always been present to produce whatever species one might desire, and do so within whatever limits one might wish. But there are always limits. There are always rules. That's how it is with intelligent design.