I can name one species which has gotten smaller: the kiwi bird is descended from a larger species. Since ontogeny recapitulates phylogeny, the kiwi bird lays the proportionately largest eggs. Don't you feel sorry for Mrs. Kiwi Bird?
I have a reply which is similar to Dr. Adequate's reply: "If Brazilians descended from the Portuguese, how come Portuguese are still here?" Obviously, some of the Portugese took the boat to the New World, some were happy where they were. Same way with chimpanzees and humans. One portion of the population wandered off and did their own thing, the other portion was happy where they were.
I tried to work this out as a chi square problem, but my Excel program wouldn't go that high. I asked someone with math skills, who said that the chances of zero Mesozoic cavemen and zero Cenozoic dinosaurs, given the Creationist claim, are 220,000,000,000,000,000 to 1. He didn't actually work it out, but he estimated.
Can you work this out? I would like to do a little more than hand wave.