One of the regular claims of evolution-deniers is that there are "no transitional fossils" or missing links. This claim is absurd. There are many, many transitional fossils. Some deniers claim that transitional has to mean that one fossil is a direct ancestor (or descendant) of another. But such direct lineages are not required -- and they could not be verified even if found. A transitional fossil shows a mosaic of features from an older and more recent organism.
There are dinosaur to bird transitional fossils, including perhaps the most famous transitional fossil, archeaopteryx.
What about whales? There are many transitional fossils available that show the evolution of whales from one form to another. Click on the graphic below for additional details on whale evolution.
On a smaller scale, consider eocoelia, a small brachiopod ("lamp shell") from lower Silurian-age rocks. It is found world-wide. In several of these locations, a succession of 4 species has been recognized (as shown below). Besides the species succession, statistical variations in the properties of the species can be observed.
And then there are the transitional horses. Click here to see the incredible transitional fossils we have tracking the evolution of the modern horse from a small dog-sized animal that lived about 55 million years ago.
And, of course, there is the recent discovery of the tiktaalik, which is thought to be a transitional form between fish and amphibian. Unlike many previous, more fishlike transitional fossils, Tiktaalik 'fins' have basic wrist bones and simple fingers, showing that they were weight bearing.
What many evolution deniers do is look at these and then say, well, show me how (a) got to (b)... there are not transitions there. Then when one is found, they pick another so called "gap" to complain about. The bottom line is that there is ample evidence that evolution has, does, and will continue to occur. It is the difference between "feeling it in your bones" and having the bones to back up your knowledge!