The Devolution Chronicles: Rise of the Chimera by Gary Wayne Clark

What if there was a world where man no longer reigned and evolution ran backwards? There is such a world, and it's closer than you think. Shipwrecked on planet Niburu, a disgraced fighter pilot turned Bounty Hunter, Commander Zacary Ryker, reluctantly leads a band of human castaways and their genetically engineered Chimera mercenaries as they are hunted by a brutal race of dimetrodons.