The elasmobranchs have had an incredibly long evolutionary history: more than 400 million years. During this extensive period elasmobranchs separately evolved many adaptations such as exquisite senses and complex reproductive modes that rival those of the most advanced tetrapods. In this chapter we review the reproductive adaptations of the elasmobranchs and show how these adaptations have contributed to their evolutionary success and genetic continuity. It is not intended here to produce a complete review of elasmobranch reproduction, as there are several excellent reviews already: Budker (1958), Wourms (1977), and Dodd (1983). Our goal is to produce a brief overview of elasmobranch reproduction that will lead the reader to the more specialized literature. We have used examples of anatomy and modes of reproduction for the few elasmobranchs that are well known. However, we must add the caveat that, although elasmobranch reproduction has proceeded along only a few paths, there is great diversity among congeners. This diversity is often expressed as different brood sizes, ovarian cycles, gestation periods, mating systems, use of different nurseries, etc. We must also state that the reproductive processes for most sharks remain unknown. Unraveling the many secrets of elasmobranch reproduction will remain a challenge for future researchers.
