ANN ARBORLike salmon in reverse, long-snouted Bandringa sharks migrated downstream from freshwater swamps to a tropical coastline to spawn 310 million years ago, leaving behind fossil evidence of one of the earliest known shark nurseries.
That's the surprising conclusion of University of Michigan paleontologist Lauren Sallan and a University of Chicago colleague, who reanalyzed all known specimens of Bandringa, a bottom-feeding predator that lived in an ancient river delta system that spanned what is today the Upper Midwest.
The new findings, scheduled for online publication Jan. 7 in the Journal of Vertebrate Paleontology, mark the earliest known example of shark migrationa behavior that persists today among species such as tiger sharks in Hawaii.
The Bandringa fossils, as reinterpreted by Sallan and Michael Coates, also reveal the only known example of a freshwater to saltwater shark migration, as well as the earliest example of a shark nursery where fossilized egg cases and juvenile sharks were preserved in the same sediments.
"This pushes migratory behavior in sharks way back," said Sallan, an assistant professor in the U-M Department of Ecology and Evolutionary Biology. "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. It resembled present-day sawfish and paddlefish, with a spoon-billed snout up to half its body length. Juveniles were 4 to 6 inches long and grew into adults of up to 10 feet.
Bandringa was discovered in 1969 and soon became one of the most prized fossils from the well-known Mazon Creek deposits in northern Illinois. Until now, researchers believed that the genus Bandringa contained two species, one that lived in freshwater swamps and rivers and another that lived in the s
|Contact: Jim Erickson|
University of Michigan