What is the Evolutionary History of Fish?
“Fish” is a word used to refer to any non-tetrapod vertebrate. The evolutionary history of fish began 530 million years ago, in the mid-Cambrian period. Some of the oldest known animals in the evolutionary history of fish are Pikaia gracilens, which resembles the modern-day lancelet, found in the famous Burgess shale assemblage, and Haikouichthys and Myllokunmingia from the Maotianshan shales of southern China. These simple jawless fish existed for approximately 100 million years until the first jawed fish evolved. These are also the earliest known vertebrates. Initially, fish were minority members in an ecosystem dominated by invertebrates, especially brachiopods, sponges, and arthropods such as trilobites. It wouldn’t be until the Silurian period, roughly 420 million years ago, that jawed fishes evolved and began to compete effectively with invertebrates. The earliest jawed fishes were placoderms, a family of fish with special head and thorax armor to protect them from predators. The
