Researchers have discovered new fossil evidence of one of the earliest known shark nurseries off the tropical coastline created 310 million years ago, according to a new study.
The findings were published online in the Journal of Vertebrate Paleontology are reportedly the "earliest known example" of shark migration and nurseries. Researchers analyzed long-snouted Bandringa shark fossils, a species which migrated downstream from freshwater swamps to a tropical waters. The nursery was found in an ancient river delta system in Illinois.
"This pushes migratory behavior in sharks way back," Lauren Sallan, paleontologist and an assistant professor in the U-M Department of Ecology and Evolutionary Biology, said in a news release. "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 Bandringa fossils reanalyzed by scientists also provided the only "known example" of a freshwater to saltwater shark migration, according to a news release. Researchers also found "fossilized egg cases and juvenile sharks were preserved in the same sediments."
"Adult Bandringa sharks lived exclusively in freshwater swamps and rivers, according to Sallan," according to a press release. "Females apparently traveled downstream to a tropical coastline to lay their eggs in shallow marine waters, a reverse version of the modern-day salmon's sea-to-stream migration. At the time, the coastline of the super-continent Pangaea ran diagonally between the Mazon Creek freshwater and marine sites."
The juvenile sharks found were 4 to 6 inches long and adults reportedly grew to be up to 10 feet long. The extinct Bandringa sharks closely resemble present-day sawfish and paddlefish, with their snout being half its body length.
"This is the first fossil evidence for a shark nursery that's based on both egg cases and the babies themselves," Sallan said. "It's also the earliest evidence for segregation, meaning that juveniles and adults were living in different locations, which implies migration into and out of these nursery waters."
Click here to read more about the Bandringa shark fossils and the oldest known evidence of their shark nurseries.
