A geological formation known as the Fayetteville Shale has preserved dozens of three-dimensional shark skeletons dating back roughly 326 million years, and all in a part of the United States not typically known for sharks, or even oceans: Northwestern Arkansas.
In a new study published in Geobios, researchers explain that the ancient seafloor where these sharks settled was low in oxygen and highly acidic. That chemical brew slowed bacterial decay enough to preserve cartilage while degrading bones and shells. What’s left is a fossil record that acts as the opposite of what’s found in most of the world: a ton of sharks and a bafflingly low number of bony fish remains, even though bony fish were widespread at the time.
A professor at Cal Poly Humboldt, study lead author Allison Bronson, says the site is “unparalleled” for understanding shark anatomy from this period, and it’s easy to see why. Cartilage is one of the rarest tissues to find in the fossil record. By studying the chemistry and sediment conditions of the Fayetteville Shale, researchers think they might be able to identify similar sites, spots where the fossil record doesn’t abide by the usual rules.
The scientists reconstructed this ancient underwater environment using X-ray diffraction, X-ray fluorescence, and high-resolution CT scans to analyze both the fossils and the surrounding rock. Many of the specimens come from the American Museum of Natural History’s Mapes Collection, a massive collection of over 540,000 Marine Upper Paleozoic fossils collected from Texas, Oklahoma, Kansas, and, of course, Arkansas.
The site, which has yielded some exceptionally preserved species like Ozarcus mapesae and Cosmoselachus mehlingi, has been given an appropriate nickname by researchers: “Sharkansas,” which is not to be confused with Sharkansas Women’s Prison Massacre, the 2015 low-budget horror movie about a shark attacking people in the swamp surrounding a women’s prison. Something tells me the film won’t be adding as much to our collective knowledge of early shark evolution as Bronson and her team’s work.
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