What do the unified plan of the structure and embryonic similarity of vertebrates prove?

As scientists suggest, the similarities at the embryonic stage and the many similar morphological features of all vertebrates indicate that they all descended from one common ancestor. It is not known exactly how he looked and when and where exactly he appeared on the planet. Despite the fact that today, due to the process of evolution, vertebrates are very different from each other, they still retain such common features as the presence of a skull, a solid container for the brain, etc.