Add edible aquatic plants!
Add aquatic edible plants, or make things like lakeweed edible for unlockable diets. You can give this ability to deinocherius and other future semi-aquatic herbis. You can also give it to hadrosaurs like lambeo, for a more varied diet, or just giving it a new niche. This will give more variety for herbivores, other than forager and berry bushes.