First fish, the earliest vertebrates

c. 518 million years ago · Event

In the Cambrian seas swims a finger-length animal with a head, a tail, and a stiffening rod down its back — the first vertebrates, jawless filter-feeders like Haikouichthys. That backbone is the family heirloom: every fish, frog, dinosaur, bird and mammal since — you included — is an elaboration of this body plan.