When one goes up a taxonomic level to the level of genera, the oldest fish genera is from the Jurassic but none of species in that genera live today. Prior to the Jurassic all fish on earth are fundamentally different than living forms. And these fossils give good evidence of gradualism in the fossil record. Anti-evolutionists often state that there are no transitional forms or sequences in which gradual evolution is seen. Yet this claim is totally false.
Forams provide the clearest and smoothest transitions between species and genera.
This is because they are preserved more easily than many other life forms. They are so small that when they fall to the ocean bottom they fit between the gaps in the sediment grains and therefore avoid being crushed. One can clearly see the gradual transformation of the earliest into the latest species. This sequence shows the animals approximately every 500,000 years. The change is gradual and imperceptible.