A kiss of death-mammals were the first animals to produce venom
(PHYSorg.com Archaeology & Fossils)

Africa is a tough place. It always has been. Especially if you have to fend off gigantic predators like sabre-toothed carnivores in order to survive. And, when you`re a small, dog-sized pre-mammalian reptile, sometimes the only way to protect yourself against these monsters is to turn your saliva into a deadly venomous cocktail.