Personally i got the 3 orcas, the megalodon, and a partridge in a pear tree.
Reasoning for my choice: the orcas will kill the great whites (as they are natural predators to great whites and literally win every fight with the great whites), along with the other 10 sharks i dont know the name of, and the megalodon will murder everything else, but im iffy on the sperm whale and maybe the dunkleosteus duo. Once the orcas are done though that whale will be torn apart, and the Dunkeleosteus duo will take longer but eventually they will be killed.