These guys are the most annoying aquatic animal there is, me being a noob, at the beginning I wanted to cross a small river, and all of a sudden these guys decimated me in seconds. When I went back I realized my two little lystrosuarous had went to avenge me so I tried to save them, but then I died once again. At this point all I wanted to do was get the few "precious" resources from my dead body, but once again they killed me. That is when I just completely gave up on rivers and everything in it.