Salmon are an amazing fish. They are born in freshwater rivers and streams. But when they get older they swim downstream and into the salty ocean’s waters where they grow up. They then return to where they were born to lay eggs and start the cycle all over again.
About 310 million years ago, scientists think that a shark called a Bandringa did just the opposite of what salmon now do. Way back then, an area south of the big city of Chicago was along an ocean coastline with rivers flowing into the area. It’s here that scientists found fossils of Bandringa egg cases and young sharks.
Fossils of the adult Bandringa sharks had been found in areas where freshwater once flowed — hundreds of miles away in what is now Ohio and Pennsylvania, so scientists originally thought that there were two species of the shark — one that lived in freshwater and one that lived in saltwater.
But new research has changed the minds of some fossil experts who say that the young and old sharks were actually the same species. The adults swam downriver from freshwater swamps to lay their eggs in the salty water along what was then a coastline.
Sharks like the tiger shark still migrate to lay their eggs near the islands of Hawaii, but they stay in saltwater. The places where they lay their eggs are called nurseries.
Bandringa were similar in looks to the paddlefish that still live in Montana’s Yellowstone and Missouri rivers. The ancient sharks had spoon-billed snouts and grew up to 10 feet long. They also, like paddlefish, fed off the bottom and had sensors in their snouts that could detect prey in murky water.
— Brett French, Gazette Outdoors editor