are thought to be present before vertabrates

Jawless fish was present before vertebrates.

Explanation:

Jawless fish has some characteristics of vertebrates and also considered as the ancestor of vertebrates on earth which is similar in appearance with the hagfish. It was present about 500 to 600 million years ago. They consist of cranium but vertebral column is absent. but with the passage of time, evolution occurs and many animals which was the descendant of this jawless fish having vertebral column or backbone in their body.