Scientists are studying a deposit of shale in northwest Arkansas to learn about sharks and their ancestors. Allison Bronson is an evolutionary ichthyologist based at Cal State Poly University Humboldt. Her recent study, published in the science journal Geobios, explains how low oxygen and high acid levels in the Fayetteville Shale deposit helped preserve more cartilaginous creatures like sharks, which are usually degraded by bacteria before fossilization. Bronson says the fossils are helping researchers confirm ideas about shark ancestry.
"There's like a treasure trove of these symmoriiform group fossils here. And so some of them have given us things like the most complete gill structures found in a shark of this age that we can use to confirm that sharks came from bony relatives. They basically have gill arches that look like bony fish gill arches."
Other fossils in the collection have transitional features that help scientists map out the evolutionary relationships of ancient fish. Bronson says the Fayetteville Shale Formation, which is around 326 million years old, is one of the few sites to study cartilaginous fossils in the world. She hopes this research will help change that.
"In the longer term, knowing a little bit more about the depositional environment and the chemistry of these fossils being preserved might help us to target other locations in the world where we can start looking for fossil cartilage."
Bronson's research has also helped create more detailed renderings of the anatomy of ancient fish, thanks to CT scanning technology that images the inside of a fossil without destroying the specimen. Sonnet 4.6
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