Fossils Of Ancient Shark Jaws Tell Scientists A New Evolutionary Tale

A 325-million-year-old preserved shark skull gives a new perspective on evolution and future research.

By Samantha Olson on April 16, 2014 9:52 PM EDT

325-Million-Year-Old Shark Skull Holds Evolutionary Promise
A rare well-preserved shark jaw has been discovered that shows scientists the evolutionary differences to modern day shark structure. (Photo: <a href=”http://www.shutter / Samantha Olson)

A 325-million-year-old shark-related species have given researchers a new perspective on the evolution of jawed vertebrates, according to a new study. The study, which was published in the journal Nature, accounts for the investigation of a rare collection of 540,000 well-preserved fossils which has revealed to scientists at the American Museum of Natural History new evolutionary evidence on the first jawed ancestors and what it could mean for human history.

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The fossils, which were recently collected and donated by Ohio University professors Royal Mapes and Gene Mapes. The unique conditions of the Arkansas ocean basin from which the fossils were discovered in, preserved the once diverse marine ecosystem from millions of years ago. According to National Geographic, an ocean basin is the largest depression on the earth's surface, comparable to that of a bathtub appearance.

"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," said Alan Pradel, a postdoctoral researcher at the Museum and the lead author of the study.

However, when Pradel and his team examined the fossils, they found the arches in the ancestral sharks were not what they expected. They found a greater difference between the modern-day shark jaw and its ancestors, ultimately suggesting that the evolution of this particular vertebrate moved at a different pace than previously thought.

"The modern shark condition is very specialized, very derived, and not primitive," said Pradel.

Shark skeletons were not previously examined with such precision and detail because of how fragile the cartilage is that makes up their frame. The frames and jaws themselves are usually found flattened by the weight of environmental factors and time. The basin preserved the skeletons and gave scientists a rare perspective into their internal structures.

We discovered that the arrangement of the arches is not like anything you'd see in a modern shark or shark-like fish," said Pradel. "Instead, the arrangement is fundamentally the same as bony fishes."

Bony fish are cartilaginous fish that are have a hard, bony plate, are covered in gills and have skeletons made entirely of cartilage. More than 28,000 species of bony fish have been documented, which makes up about 90 percent of the world's fish population, according to Sea World's scientific classification.

A fossilized skull that was found in the basin has been determined as a new species, Ozarcus mapesae, which was preserved in a nearly perfect three-dimensional state despite its fragility. Sharks have existed on record for 420-million years, which is why scientists weren't surprised such evolutionary changes were discovered.

Scientists at the Museum worked with the European Synchrotron's high resolution x-rays to get a detailed look at the prehistoric arch of the jaws. The jaws from millions of years ago were so dissimilar to the ones found in sharks today that scientists believe it has significant meaning to how vertebrates will be studied in the future.

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