Sharks are not the "living fossils" many biologists believed them to be, based on a study of a new fossil. Over the course of time, these mighty hunters became even more ferocious, better able to hunt and consume their prey.
A newly-discovered 325-million year-old shark fossil is now revealing secrets of ancient members of these marine animals. This artifact is not the oldest-known shark fossil, but is the most complete specimen of its type in the world.
Ozarcus mapesae was first discovered in Arkansas by a husband and wife team, Royal and Gene Mapes. The two donated the fossil to a local museum. The artifact is three feet long and shows that the creature had very large eyes. At the time it was alive, the area was also home to large squid-like creatures.
The fossil is "the earliest identified chondrichthyan in which the complete gill skeleton is three-dimensionally preserved in its natural position," researchers say.
This carnivorous fish had body features resembling both sharks and spiny fish, suggesting modern sharks have evolved significantly since that time. Some of these changes made sharks the mighty hunters they are today.
Researchers performed CT scans and examined the artifacts with a synchrotron to study the fossil without harming the relic. This revealed jaws and gills of Ozarcus mapesae resembled bony fish more than modern sharks.
"Sharks were considered for a long time as 'living fossils' that should not have changed a lot, but they have probably more than 420 million years of evolution behind them!" Alan Pradel, lead author of the article told Discovery News.
Shark-like species first evolved around 400 million years ago, and the first true sharks developed one hundred million years after that time.
Paleontologists disagree on the identity of the first true shark. Jaw structures of modern sharks are significantly changed from the animal that created the newly-discovered fossil.
John Maisey of the American Museum of Natural History helped identify the ancient artifact. He believes the change may have allowed the predators to open their mouths wider, to attack larger prey.
Paleontologists have largely ignored the evolution of sharks, believing they had not changed much over time.
Ozarcus mapesae was named in honor of the location they were found, the Ozark region of Arkansas and the paleontologists who made the finding.
Study of the ancient shark fossil was detailed in the journal Nature.
