The Brothers were rivals to Half-Tooth. They threatened Half Tooth and worked together against him. The rival males ultimately chase off Half Tooth (actually Half Tooth backs off wisely without any serious injuries, feeling that the two males would be too strong for him). They kill his cubs and completely take over. They pushed Half Tooth to the scrub forest (although Half Tooth sometimes checked up on his old clan).
However, a Megatherium, who wanted to eat meat as diet supplement, charges the pride of Smilodon, in order to eat some of the carrion. In the process, the Megatherium kills the dominant brother. The less dominant brother soon fights Half Tooth again (alone) and gets fatally injured. His carcass gets scavenged by Terror Birds.