I have a Elder Cryo tamed and my friend has an elder Valkyrie tamed, but when we attack the same thing together, we each do less damage than we do without the other nearby.

We noticed a couple times where one of us was attacking something like a 1200 wild valkyrie, and as soon as the other gets close enough, damage per hit drops to about half on that wild dino.

Is this a bug or on purpose for some reason?