But did they do it, and do it successfully. The definition of a species is the production of viable offspring. Not an easy thing to discern with a pile of fossilized bones. A bull dog has a very different skull than a collie, but there are enough other traits in common to know that both of their skeletons indicate they are dogs, and not cats. Yet we have living cats and dogs to examine, and to know that they are different species. My paleontolgy prof put it this way: "fossils of extinct critters mating are pretty hard to find."

The thing that people forget about fossils is that very few animals die in a way that permits fossilization. It's not really a random sample of the paleo environment. They have to die in just the right place at the right time to get preserved. How many human remains would remain after 75 million years?

Also, there is exposure. The Morrison Formation, which has produced many dinosaur fossils, covers several states, but only outcrops as a thin band at the edges of a large basin. We only have access to a small percentage of this rock unit.