ANN ARBOR, Mich., Jan. 7 (UPI) -- Fossils have shown the earliest known example of shark migration, a behavior that persists today among species such as tiger sharks in Hawaii, researchers say.
More than 300 million years ago long-snouted Bandringa sharks migrated downstream from freshwater swamps to a tropical coastline to spawn, leaving behind fossil evidence of one of the earliest known shark nurseries, a paleontologist at the University of Michigan said in a release Tuesday.
"This pushes migratory behavior in sharks way back," evolutionary biology Professor Lauren Sallan said. "These sharks bred in the open ocean and spent the rest of their lives in fresh water. No shark alive today is known to do that."
The long-extinct Bandringa is likely one of the earliest close relatives of modern sharks, resembling present-day sawfish with a spoon-billed snout up to half its 10-foot body length.
When first discovered in 1969, the genus Bandringa was thought to contain two species, one that lived in freshwater swamps and rivers and another that lived in the shallow ocean.
But after re-evaluating fossils from 24 individuals found in deposits in northern Illinois, Sallan and Michael Coates of the University of Chicago concluded that Bandringa was a single species that lived, at various times during its life, in fresh, brackish and salt water.
Adult Bandringa sharks lived exclusively in freshwater swamps and rivers, Sallan and Coates said, with females apparently traveling downstream to a tropical coastline to lay their eggs in shallow marine waters.