In the Mazon Creek fossil beds of Grundy County, Illinois, scientists have found evidence that a 310-million-year-old shark, once thought to have encompassed two different species, was in fact one species that lived in both fresh and salt waters.
Lauren Sallan of the University of Michigan and Michael Coates from the University of Chicago reexamined the remains of 24 organisms, delving into the anatomy and lifestyle of a 310-million-year-old shark. Bandringa was a suction feeding shark similar to today’s sawfish. Paleontologists had previously determined that Bandringa was a genus consisting of two species: one who lived in fresh water, and one that made its home in the ocean. But a new study in the Journal of Vertebrate Paleontology says otherwise: Bandringa was a sole species that produced offspring in marine waters before travelling to make a new home in fresh water.
Bandringa’s most prominent feature is its long snout, which accounts for half of the shark’s total body length – which could be up to 10 feet long as a mature adult. Sallan and Coates discovered that Bandringa had jaws that pointed down, further facilitating its suction feeding activity. They found that needle-like projections on Bandringa’s body helped it to sense small fish swimming in surrounding waters for a tasty meal.
Sallan and Coates analyzed juvenile Bandringa fossils from saltwater sites, found alongside egg remains, where 310 million years ago, a shark nursery was teeming with young Bandringa individuals. Bandringa adults would travel to these marine nurseries from fresh water areas, where they bore offspring, then move back to their fresh water homes for the remainder of their lives.
Paleontologists were misled into believing Bandringa was two separate species due to the tendency of organisms to fossilize depending on what kind of water they live (and die) in. Salty ocean waters are especially good at preserving soft tissue remains, while fresh waters keep bones and cartilage shapely for millions of years.
Source: Sallan, L. C., & Coates, M. I. (2014). The long-rostrumed elasmobranch Bandringa Zangerl, 1969, and taphonomy within a Carboniferous shark nursery. Journal of Vertebrate Paleontology, 34(1), 22-33.
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