Photo of a Rare Transitional Water to Land Transitional Species circa 1952
Now, just a bit more seriously, one of the common claims that Young Earth Creationists make is that there are no transitional fossils. In actuality, given the low probability of anything ever becoming a fossil, it is amazing how many transitional fossils have been found. Nice lists of transitional fossils can be found here, here and here. There are at least hundreds, if not thousands of specimens demonstrating characteristics between species, with examples for fish, reptiles, dinosaurs, birds and mammals.
What is even more impressive than the transitional species shown above are extant transistional species such as the mudskipper, a fish that lives mainly on land and breaths air, and the more famous platypus.