Alien Animal: Thunderhorn

At forty feet tall and measuring as long as Naval patrol boat, Thunderhorns are truly massive creatures. They feed off of the eight foot tall grass that covers the plains of Athena.
As herd animals, they travel in large family groups. These herds are matriarchal in nature, being composed mostly of females. The males, called "bulls", live semi-solitary lives. They tend to follow at the rear of the migrating herd, being the defenders of the caravan of these mammoth creatures.

Big. Thats the only word that popped to mind when I first started the Alien Animal series. I wanted something on a dinosaurian size with the attitude of a pissed off rhino. Of course, even Thunderhorns have predators....heh heh heh....