14 DAY TRIAL // For many years, biologists have argued that sharks have remained almost identical to their distant ancestors that lived hundreds of millions of years ago. A new scientific study from an international team of researchers suggests that, while sharks may retain an unchanged external appearance, they have changed a lot on the inside.
This conclusion was derived from studies of a new fossil identified by researchers including paleontologist John Maisey at the American Museum of Natural History (AMNH) in New York. Details of the investigation were published in a recent issue of the top scientific journal Nature. The team included scientists from the University of Chicago and the Uppsala University in Sweden.
A detailed analysis of the fossil has revealed that the ancient ancestor of modern-day sharks looked pretty much the same as its descendants, but it was not equally well-suited for the hunt in terms of internal efficiency. “They have evolved through time to improve upon the basic model,” Maisey says.
The research group says that the fossil discovered recently was not of a megalodon, the largest shark to have ever lived. The creature that left it behind was likely between 60 and 100 centimeters (2 to 3 feet) long and featured only tiny teeth. However, the ancient shark lived around 325 million years ago, which means it can provide researchers with a glimpse into a very distant past.
Maisey says that the tiny shark would have certainly delivered a painful bite to its victims, given the row-after-row disposition of its teeth. Even figuring out a simple thing as tooth distribution was very complicated, because the old fossil comes in the shape of an average-looking brown rock. Scientists were only able to analyze it by using computer tomography (CT) and other imaging techniques.
Using this approach, Maisey and his group were able to image the head of the ancient shark. They determined that the anatomy of the creature had very little in common to that of its modern-day counterparts. The gill skeleton on the ancient shark looks a lot more like that of modern fish than that of modern sharks, NPR reports.
UC evolutionary biologist Michael Coates says that these results turn an old theory on the origins of shark gills on its head. Until now, experts believed that the gills in ancient sharks predated those in modern fish, but this research suggests that the gills may in fact have developed in ancient fish in the first place.
“That bucks a trend that's been in the literature for years and years that sharks are somehow primitive living fossils,” Coates explains. The main implication of this finding is that fish may have developed this type of gills, and that the gills on modern-day sharks may be an evolutionary adaptation from that ancient gill system.