Where are all the fossils showing goop evolving into dinosaurs, and then later, humans?

Duly noted. I'm more intrigued about the lack of active transitional species. If conditions were ideal for their sufficient proliferation at one time, then why are they all gone now? Why don't we have Neanderthals today, who themselves have evolved from the preceding species in the evolutionary line? Also, if the notion of species devlopment is a continuous principle, then why can't similar species -- such as humans and primates -- mate and have offspring?