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Ancient sharks reared young in prehistoric river-delta nursery

1/7/2014

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By Jim Erickson
Jan 07, 2014

Illustration: John Megahan

Like 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, published online Jan. 7, 2013 in the Journal of Vertebrate Paleontology, mark the earliest known example of shark migration – a 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.

Sallan’s research, and an accompanying painting by EEB artist John Megahan, is receiving widespread media attention (nationally and internationally), making the front page of Discovery,Science and an upcoming interview with Scientific American and the L.A. Times.