Bandringa sharks returned to saltwater to breed (Image: John Megahan, University of Michigan)

A prehistoric shark species is the earliest animal known to migrate, over 300 million years ago. The sharks lived in rivers but swam down to the sea to breed and care for their young.

Bandringa were primitive sharks that lived about 310 million years ago. They did not look much like typical modern sharks, having long spoon-shaped snouts.

Until recently scientists thought there had been two species of Bandringa, one that lived in fresh water and one that lived in the sea. But according to Lauren Sallan of the University of Michigan in Ann Arbor, there was only one species. The sharks migrated from their freshwater habitat to a saltwater nursery to reproduce.


Sallan and her team examined Bandringa remains from three sites in the Mazon Creek deposit in Illinois, including egg casings, bones, and soft tissue from juveniles and hatchlings. One site was originally on the coast but the others were inland. They found no evidence that fossils from the different sites belonged to different species.

Instead, Sallan says, “the three sites are segregated by age”. Juveniles and hatchlings were found alongside the eggs in the coastal site, while the bodies of adults were found inland. “That’s what lets us see the migration.” The coastal site is the oldest known example of a shark nursery.

Journey of the shark

Sallan says the Bandringa are far and away the oldest known example of a migrating animal. In 2011, palaeontologists found the first solid evidence that sauropod dinosaurs migrated seasonally, about 150 million years ago.

It certainly seems to be the earliest evidence of migration in a vertebrate, says George Engelmann of the University of Nebraska at Omaha. But migration may have an even longer history. “I could readily entertain the possibility that earlier vertebrates were making migrations between fresh water and salt,” he says. “It may go back quite a ways before this.”

Most modern sharks migrate from the open ocean to near shore to lay eggs or give birth. They do so to protect their young from predators, including other sharks. The Bandringa sharks switched from a marine habitat to a freshwater one, but continued to return to saltwater to breed and lay their eggs.

In theory, the Bandringa‘s young might have been perfectly safe in their freshwater environment, but Sallan suggests that they were locked into their ancestors’ behaviour of breeding in the sea. Recent genetic evidence has shown that sharks return to where they were born to breed, and palaeontologists have long suspected that prehistoric sharks also migrated.

The Bandringa must have had sufficient memory capacity to return to the same location every time they bred. They would also have needed processes to control their salt levels as they moved from fresh water to saltwater and back again. Modern sharks do regulate their salt levels, but most are only ever in saltwater. “Because they made the switch from saltwater to fresh, the Bandringa would have required a system to control their salinity levels in fresh water as well as saltwater,” says Sallan.

Journal reference: Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2013.782875