Even though they're often thought of as "living fossils," researchers say that modern-day sharks are sleeker than their prehistoric ancestors -- 325 million years ago.
Extremely well-preserved, a fossil of what is now named Ozarcus mapesae was first discovered by professors Royal Mapes and Gene Mapes, and later donated by Ohio University to the American Museum of Natural history. A closer look at the fossil revealed that modern-day sharks are quite advanced when compared to their prehistoric relatives.
"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," Alan Pradel, researcher and author of the study, said in an statement. "But we've found that's not the case. The modern shark condition is very specialized, very derived, and not primitive."
The heads of all fish species -- including sharks -- are segmented into the jaws and a series of arches that support the jaw and gills. Shark skeletons are made of cartilage, not bone, and as a result their fossils are fragile. However, this fossil allowed a rare close-up look at the evolution of an early species.
"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," John Maisey, a curator in the paleontology division and one of the authors on the study, said in a statement.
Working with other scientists at the European Synchrotron, the preserved fossil underwent high-resolution X-rays to get a more detailed view at the shape and organization of the arches. They soon discovered that the arrangement of the arches is not anything like that of a living shark. Instead, the arrangement is similar to that of bony fish.
"Bony fishes might have more to tell us about our first jawed ancestors than do living sharks," Maisey said.
The discovery of evolution was not unexpected, as sharks have existed for nearly 420 million years. Other recent studies, such as one about the development of teeth and jaws in the earliest jawed vertebrates, may have a profound implication in modern humans' understanding of the evolution of their ancestors, researchers note.
The study, which included Synchrotron scientist Paul Tafforeau and researcher Jon Mallatt of Washington State University, was published April 16 in the journal Nature.© 2014 CBS Interactive Inc. All Rights Reserved.
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