Nov 11, 2018 at 4:00 AM

More than 400 million years ago, ancient oceans were teeming with many types of fish that might seem alien today, such as the osteostracan (pictured).

Scientists have long wondered where these extinct fish groups and their living relatives first evolved.

Researchers created a database with more than 2,700 fossil records from 480 million to 360 million years ago. The study, published in the journal Science, suggests that fish swam in the shallows around the coasts of supercontinents before diversifying.

They believe ‘‘there’s something going on with water chemistry … in these active and dynamic environments,’’ said Ivan Sansom, a paleobiologist who is an author on the paper.