A. If evolution is a slow process occuring over millions of years where are all the transitionary species in the fossil record?
You can make a good case for evolution within major grouping such as 'fish, 'bird', 'reptile', etc., but where are all of the 'fish in the process of becoming amphibians'and 'reptiles in the process of becoming birds', fossils?
First, evolution is a slow process, but it is not a uniform process. The human/ape split is a good example. Something like six+ million years ago the forests of Africa were shrinking and the grasslands were expanding. Apes were getting squeezed by the reduced habitat. One group of apes gradually adapted to the forest edges, then the grasslands. We are descended from that group.
They changed considerably in the ensuing six million years, as they had to adapt to new and different conditions and environments, while the groups that remained in the forests changed but little--they were already adapted to their environment.
Since evolution is a process, it would seem logical to deduce that 'pure' fish, birds, etc. ought to be mere tiny waypoints on the evolutionary spectrum, and that the fossil record ought to consist almost entirely of transitionary species.
You are entirely correct. All species are transitionals, and I don't know what a "pure" species would be. Even within a species there is considerable variation. Skin color is an example; within our species there is a large range, with most folks pretty well adapted to the area in which they live. But within each group there is a range as well. If the climate changes, some within each population are better suited than others, and tend to do better.
But because the process of evolution is generally slow, we don't really see it in most large critters. Bacteria can become resistant to antibiotics in a few decades, as they have a much shorted generation span. For the larger mammals, most look quite a bit like their parents. Where you can see some real evolution is in what are called ring species, where, as an example, a species living around a high mountain changes gradually from area to area, until the two endpoints which meet on the other side are no longer interfertile, although going in the other direction each group is interfertile with the adjacent group (google "ring species" for some fascinating reading).
B. Why aren't we seeing a lot of evolution going on right now? There doesn't seem to be any particular scientific reason why this should not be happening.
Again, you are correct. Evolution is ongoing all around us. But its real slow, and we just have too short an attention span! We look at change over decades as slow, while evolution looks at millenia and beyond for most changes.
But, we may be in the process of losing our third molars! As we have shifted from tough natural plant products to softer agricultural and processed foods, the chewing muscles have become smaller, the face and jaw have become smaller, and the teeth get less interproximal wear (wear between adjacent teeth). So, when the third molars erupt, sometimes there is not enough room and some people get serious dental problems. This is enough natural selection that those without third molars may have a tiny advantage over those with third molars worldwide. Give it 50,000 years or so and you might just see the third molars become rare.
Shouldn't we be up to our eyeballs in 'evolving' creatures? Shouldn't we be seeing all sort of creatures in various states of evolving? Yet all we see are the same old 'insects', 'fish', 'birds', 'reptiles'.
But each of these is halfway from its ancestors to its descendants! We can see many of the ancestor, but we can't tell what the descendants may look like. That's half the fun!
How do you know it is not uniform?