Start to replicate I think
They were similar to modern humans in that they were bipedal (that is, they walked on two legs), but, like apes, they had small brains. Their canine teeth were smaller than those found in apes, and their cheek teeth were larger than those of modern humans.
_________ is the only element capable of forming stable, extended chains of atoms bonded into single, double, or triple bonds. Hydrocarbons containing carbons which are bonded by only single bonds. Hydrocarbons containing at least on Carbon-Carbon bond which is a double bond.
Many reasons to be honest but the main one is because of erosion and the water levels (rising and falling)