Ancient Shark Fossil Reveals Modern Sharks are Evolutionarily Advanced

Posted on April 17, 2014

A ancient shark fossil reveals that modern sharks are evolutionary advanced despite having retained their "sharkiness" over millions of years. The fossil of a 325-million-year-old shark-like species also reveals new insights into the early evolution of jawed vertebrates. The study was led by scientists at the American Museum of Natural History.

Alan Pradel, a postdoctoral researcher at the Museum and the lead author of the study, says in a statement, "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 shark-like fishes. But we've found that's not the case. The modern shark condition is very specialized, very derived, and not primitive."

The new study is based on an extremely well-preserved shark fossil collected by Ohio University professors Royal Mapes and Gene Mapes in Arkansas. An ocean basin in what is now Arkansas was once was home to a diverse marine ecosystem. The fossilized skull of the new species (Ozarcus mapesae) was part of a recent donation of 540,000 fossils from Ohio University to the Museum. Shark skeletons are made of cartilage (not bone) and their fossils are usually very fragile and found in flattened fragments. The Ozarcus mapesae is special because it was founded well-preserved in a nearly three-dimensional state. It was imaged with high-resolution x-rays with the help of scientists at the European Synchrotron, the ESRF.

John Maisey, a curator in the Museum's Division of Paleontology and one of the authors on the study, says, "This beautiful fossil offers one of the first complete looks at all of the gill arches and associated structures in an early shark. There are other shark fossils like this in existence, but this is the oldest one in which you can see everything. There's enough depth in this fossil to allow us to scan it and digitally dissect out the cartilage skeleton."

Maisey told Reuters in an interview that "we found the Model T of sharks."

Here is a video of museum curators Maisey and Neil Landman talking the new fossil sharks and ammonites added to the Museum's collection. Discussion of the Ozarcus mapesae fossil shark head fossil of starts at the 2:14 mark. A video of the X-ray synchrotron scan of the fossil rotating can be found here. Take a look:

The research paper was published here in the journal Nature.

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