Of all the arguments that are used by religious people against evolution, the most fraudulent is that there are no transitional forms between species. People who say this either willfully ignore the evidence that does exist or think that a transitional form must be a hybrid between two currently existing species.
Do you think that no one could be that stupid? Behold the infamous crocoduck argument.
Yes, some creationists like Kirk Cameron are so ignorant of the theory of evolution that they will actually go on national TV and make fools of themselves in that way.
Fossilization can occur only under very special conditions which is why they occur so rarely and why the discovery of transitional forms like Tiktaalik are so notable.
But if someone should raise this argument with you, point them to whale evolution. Since 1978, we have pieced together in step-by-step form how a mammal that can live in the ocean came about and it is a truly remarkable and well evidenced story. The short video showing how the story was pieced together is fascinating.
It’s the tale of an ancient land mammal making its way back to the sea, becoming the forerunner of today’s whales. In doing so, it lost its legs, and all of its vital systems became adapted to a marine existence — the reverse of what happened millions of years previously, when the first animals crawled out of the sea onto land.
Some details remain fuzzy and under investigation. But we know for certain that this back-to-the-water evolution did occur, thanks to a profusion of intermediate fossils that have been uncovered over the past two decades. (My italics)
Starting with wolf-sized carnivores that existed between 60 and 37 million years ago, we see in the fossil record the steady evolution of features that were once suitable for living on the land becoming adapted to water.
None of these animals is necessarily a direct ancestor of the whales we know today; they may be side branches of the family tree. But the important thing is that each fossil whale shares new, whale-like features with the whales we know today, and in the fossil record, we can observe the gradual accumulation of these aquatic adaptations in the lineage that led to modern whales.
The story of the whale likely will not convince your hardcore creationists because they have learned how not to see things they don’t want to see. And the truly loony will say that god deliberately planted these fossils to give us the impression that evolution occurred.
But the story of the whale cannot fail to have an impact on those who are genuine seekers of truth.