Ancient Shark Fossil Shines Light on Modern Jaws

For years, researchers assumed that sharks were a fairly primitive form of life—one that hit the genetic jackpot early and had thrived without changing much throughout the eons. But what Museum scientists uncovered while analyzing a newly discovered 325-million-year-old fossil of a sharklike fish could change that line of thinking.

“Sharks are traditionally thought to be one of the most primitive surviving jawed vertebrates. And most textbooks in schools today say that the internal jaw structures of modern sharks should look very similar to those in primitive sharklike fishes,” says Alan Pradel, a postdoctoral researcher at the Museum and the lead author of a study that was published in the April 16, 2014, issue of Nature. “But we’ve found that’s not the case.”

Bony fish have jaws that are rigidly connected to their skulls by bone structures, while shark jaws are attached with more flexible ligaments. The discovery of an early jaw in this new fish fossil suggests that this early sharklike fish, known as Ozarcus mapesae, had structures known as gill arches that more closely resemble the gill supports of modern tuna than the jaws of modern sharks.

 

“The European Synchrotron used in this study is the Hubble Space Telescope of paleontology.”

John Maisey Curator

 

That evidence is only available thanks to the beautifully preserved state of the fossil, one of more than half a million marine fossil specimens donated to the Museum by Ohio University. That preservation allowed Museum researchers to pick out details that would have otherwise been lost to the ages.

“There are other shark fossils like this in existence, but this is the oldest one in which you can see everything,” says John Maisey, curator in the Museum’s Division of Paleontology and one of the authors of the study. “There’s enough depth in this fossil to allow us to scan it and digitally dissect out the cartilage skeleton.”

 

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3D reconstructions of the skull of Ozarcus mapesae, the ancient fish studied by Pradel and Maisey.


That scanning was performed with assistance from partners at the European Synchrotron. This device, which Maisey has called the “Hubble Space Telescope of paleontology,” can offer a look deep inside fossils without damaging them by bombarding specimens with high-energy x-rays.

Synchrotron results provided high-resolution 3D scans of Ozarcus mapesae that allowed researchers to examine the fossil in stunning detail. This more detailed understanding suggests that researchers interested in learning how early jaws developed might have more to learn from early fish fossils than modern sharks.

 

Funding for this study was provided in part by the Herbert & Evelyn Axelrod Research Chair in Paleoichthyology at the Museum.