The king sprintzilla replaced its ancestor, the tyrant sprintzilla. After the desert chitinbane wiped out most of the saucebacks in the region, it was limited to Ittiz River and Ittiz Swamp. There it had large enough saucebacks to hunt.
Its front limbs have completely disappeared and it has doubled the amount of "leaves" on its back. These leaves not only photosynthesize, but regulate heat in the arid environment. Its spikes on its tail have become smaller and more numerous to keep any creature from smothering its butt-nostrils. Its beak has become even larger and has many more "teeth" to help saw through the chitin of saucebacks.
Like its ancestor, its eyes can see well at dusk and night. Its tympanic membrane has improved, so it can hear prey better. Due to the extinction of the stickysilk scuttlecrabs it no longer needs to dissolve silk so now its saliva helps in dissolving chitin. This makes biting through sauceback exoskeletons much easier to get to their meaty insides.
They are even meaner than tyrant sprintzilla because there is only so much to eat for a large apex predator. They will fight and even kill each other over territory and food. Only the strongest will reach adulthood. Males with bigger beaks get the females. Males will battle to the death over a mate. Their tough hide not only protects them during mating brawls, but from the sharp weapons of its prey.