Again, If you truly seek to know the answer, an insight lies in the Burgess Shale in the Canadian Rockies. Fortunately, after the discovery of these oldest of fossils, they were studied over decades. Gould's book Wonderful Life: The Burgess Shale and the Nature of History is the story of the men who made the studies and what they accomplished. It is an extremely interesting endeavor requiring years and years of dedication. Many here don't like stephen gould but this book is not his research. He is writing about the Burgess Shale scholar's efforts and then describes what was discovered.
As a teaser for you, one of the fossils is the first known chordate..... backbone. that would be our early ancestor. I think that since the initial discoveries, there might be one or two fossils that predate that ancestor.
There is an opportunity for a road trip to the Royal Tyrell Museum in Drumheller Alberta. The location is in the middle of the most fertile dinosaur fossil producing strata on earth and has lots and lots of full dinosaur skeletons. The answer to your evolutionary questions can largely be answered by a visit to this truly world class museum.
