The first truly mineralized vertebrate skeletons would have evolved in the Ostracoderms, a group in the Gnathostomata branch, as a dermal skeleton independent of the Echinoderms, and happened simultaneously during a small window in time during the Ediacaran-Cambrian transition. This suggests a quick and synchronized evolution of biomineralization in various Phyla, e.g., during the Cambrian explosion. The increase in skeletal mass is a biomechanical necessity for increasing body size. The development of phosphated postcranial skeletons in vertebrates gave, among other things, biomechanical support for the colonization of land. In truth the move to land was a gradual one. Fingers did not form from the modification of fins as they have different embryogenic beginnings. The gradual reduction of fins probably allowed the endoskeletal component increase which in turn produced fingers; the change may have resulted in different durations of diverse development phases. The most distinct contrast between fish and tetrapods is the evolution of fingers, the articulations associated with limbs, fists, ankles, elbows and knees.
Similarities in the development of mineralized skeletons in animals still in existence probably doesn’t reflect shared ancestry but rather shared convergent or parallel evolution. Mineralized tissues possibly come from the mineralization of substrate of preexisting skeletons (e.g., cuticle), being possessed by a former skeletal structure on the creation of mineralized structures. It might be the case that parallel evolution of biomineralization in the Cambrian not only assimilated the preexisting molecular machinery but also used the non-mineralized derivation of a common ancestor.
