Chemical and Physiological Change from Calcium Carbonate to Calcium Phosphate in Skeletal Structures

The substrates that comprise skeletal structures have evolved over more than 480 million years. We review chemical and physiological factors that may have driven the evolutionary process from an original calcium carbonate composition of skeletal structures to the calcium phosphate-based bone physiology that we observe in vertebrates today. A review of this topic is not without challenges, however. Many of these changes occurred nearly 480 million years ago, as evidenced by fossils from extinct creatures; these relics, and their correlations to extant organisms, are the only tools we have to develop insight into these changes [1]. In this paper, we discuss factors that may have contributed to the divergence of skeletal constituents to try to gain insights into this intriguing and notable physiological evolution. While the biology of these conditions is ultimately complex and no process can fully account for the millions of years of change, the goal is to propose a model and initiate a dialogue that could lead to, for example, targets for drug delivery, orthopedic treatment, prosthetics, bone pathologies, and other ideas for readers to build upon for future research and investigation. Locomotion and the storage and rapid retrieval of phosphorus, a critical mineral, provided a significant impetus for evolution. This review focuses on the chemical evolution toward CaPO4 from CaCO3 that addressed the need for 1) Storage of energy metabolites in the body and 2) Improved retrieval of these metabolites.