Since I mentioned it above, how about the fish yo tetrapod transition of the mid to.late devonian. The anatomical change being fused skull to an unfused mobile neck/pectoral girdle, fused wrists to unfused rotating wrists, the introduction of robust shoulders, spiracles on the skull, and a primitive rib cage amd more.
Fish dominated in the early devonian and in earlier times. No land vertebrates existed. Terrestrial vertebrates existed in the late devonian and beyond. So by finding rock of the correct age, and finding rock of shallow.marine origin, as opposed to marine rock or terrestrial rock, scientists were able to dig down 10 feet below grade to find this shallow.marine rock with several part fish-tetrapod fossils depicting the transition from fish to tetrapod and from water to land.
Tiktaalik could have been in the ordovician or Cambrian or silurian. It could have been anywhere in the mesozoic or cenozoic. But it was ultimately found right where evolution predicted it to be. And it doesn't contain morphological traits that would disprove the theory, such as mammalian traits or any sort of bird or reptile derived traits. It has homologous traits of ancestral origin, but no traits or later derivation.