Tropaeum ("Trophy") is an extinct genus of ammonitecephalopod found throughout the oceans of the world during the Early Cretaceous. As with many other members of the familyAncyloceratidae, there was a trend among species within this genus to uncoil somewhat, in a very similar manner in the genus Lytoceras. The largest species, T. imperator of Australia, had a shell a little over one meter in diameter.