Based on what we have seen in the 20 minutes of IGN footage and the 22 minutes of event footage compared to the March 29th demo.

Hunting mechanics so far:

Not different than the march 29 demo in any significant way other than maybe Cerato can kill edmontosaurus now, may have been improvements we didn't see regarding things like the spinosaurus taking down the maiasaurus. Aggressiveness is also shown to be boosted when certain genes are modified where animals will attack each other more regularly via the scripted animations or the death duel. (personal concern level: high)

Herding mechanics so far:

3 man circle and apparently dinosaurs who are social stick together but don't really interact or anything..... (personal concern level: moderate)

Fear mechanics so far:

Legit not even 1 instance of this happening outside a scripted event. Edmontosaurus is completely unfazed by Ceratosaurs as is every other herbivore until they initiate a scripted event.

(personal concern level: Literally higher than for anything else in the entire game)

Other:

Walking has been added for more creatures that we did not see it for in the March 29 demo, can't think of anything else very major. Guests have not changed at all from what I saw in the earlier demo either, apparently they will react to rain/storms by covering themselves with their arms and hands, umbrellas I've been told are confirmed not in the game (odd).