Well, there we go. Zipp City US of A, it would appear you've established the thrust of your topic here. Oh, and Welcome to A2K, by the way.
Now, as to your "framework" framework - vertebrates did not spring forth equipped with bilaterally symetrical decidigit appendages. Appearin' durin the Ordovician period, some half-billion years ago, the first vertebration, as displayed by
Agnatha was a means of providin' for a food intake equipped with crushin'-tearin' gear; moveable bony plates which eventually evolved into jaws and teeth.
Myllokunmingia fengjiaoa the earliest known vertebrates, gave rise to
Placoderms, the vertebrates with the earliest known hinged jaws, havin' elements both of endoskeleton and exoskeleton, and evidencin' a number of design changes which did not make it into succeedin' models, such as the cartelagenous fishes and the bony fishes, which begin appearin' in the fossil record some hundred-plus million years on from the proto-vertebrate agnathae.