GEOLOGY

Detailed explanation-1: -The first fish were primitive jawless forms (agnathans) which appeared in the Early Cambrian, but remained generally rare until the Silurian and Devonian when they underwent a rapid evolution.

Detailed explanation-2: -Haikouichthys, from about 518 million years ago in China, may be the earliest known fish.

Detailed explanation-3: -The first ancestors of fish, or animals that were probably closely related to fish, were Pikaia, Haikouichthys and Myllokunmingia. These three genera all appeared around 530 Ma. Pikaia had a primitive notochord, a structure that could have developed into a vertebral column later.

Detailed explanation-4: -The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish. The most formidable of them were the armored placoderms, a group that first appeared during the Silurian with powerful jaws lined with bladelike plates that acted as teeth.