by the upper triassic the small cynodonts included the rodent-like tritylodonts (possibly related to or descended from travsersodonts), and the tiny, shrew-like, trithelodonts, which evolved into the first mammals. the trithelodonts died out during the jurassic, and the tritylodonts survived in the cretaceous, but the mammals continued to evolve. many mammal groups managed to survive the cretaceous–tertiary extinction event, which wiped out the non-avian dinosaurs, allowing the mammals to diversify and dominate the earth.