Convergent evolution is once again pointed out in the linked article.
"Predatory reptiles called ichthyosaurs cruised the oceans between 230 million and 90 million years ago. In a classic case of convergent evolution, their body and fin shapes resembled those of today's dolphins, tunas, and great white sharks—the fastest swimmers in the sea. A new study shows that the convergence even extended to the molecular composition of the animals' skin."
