There are accounts of saltwater crocodiles preying on dolphins, which is the modern day equivalent of this.
At equal weights, crocodiles tend to dominate predatory sharks like the bull shark and tiger shark. And sharks defeat single dolphins when size is equal.
Dolphins need a pod or a big size advantage to defeat predators like sharks because they are at a major weaponry disadvantage.
At equal weights a crocodile will be much longer than a dolphin or a shark. (For example a 16 foot saltwater crocodile will be equal to a 13 foot great white or tiger in weight). Which helps because it will have a significant reach advantage. It's skull will dwarf either at equal weight as well as it's teeth.
There is a study showing that terrestrial animals tend to be stronger than aquatic animals of equal weight, which makes sense because they have to support their weight against gravity everyday whereas aquatic animals have buoyancy holding them.
Crocs being semi terrestrial helps them in the strength department. This is further helped by the fact that the vast majority of their weight comes from bone and muscle mass (their vital organs are tiny for their size). Whereas dolphins and sharks have very large vital organs (shark for example have livers alone that can be 1/3 of their total weight).
And while dolphins and sharks are definitely faster in a straight line, crocodiles with their flexible reptilian spines can turn in on themselves much easier than sharks or dolphins, which require much wider turns than crocs do.
(Seriously as agile as great whites are, seals often swim right behind them or even right next to their torso to AVOID their jaws because they realize they are safer from their jaws at these tight turn radiuses).
The shark even with it's tough skin gets dominated by crocs at equal weight. A dolphin with its soft, wet hotdog skin is going to get hurt very easily.
So yeah at equal weights I support any croc over any shark or dolphin. And with a weight advantage? Well then it becomes a clear predator prey scenario in the croc's favor.
