‘What big teeth…’
By - The Washington Times - Wednesday, July 16, 2003
What has 7-inch teeth, a mouth that’s 6 feet in diameter and can swim 35 feet per second? The giant white shark. But beach-goers need not fret, because this 60-foot monster shark has been extinct for millions of years.
“I don’t think 21-foot sailboats would be quite as popular if these sharks were still around,” says Bretton Kent, an instructor at the University of Maryland’s College of Life Sciences. “You’re talking about a shark who could’ve taken out one of Columbus’ smaller ships.”
For about two decades, Mr. Kent has been doing research on the giant white shark, which is estimated to be about three times larger than today’s top ocean predator, the 23-foot great white shark — a contemporary of the giant white several million years ago.
By studying fossils of the giant white shark’s teeth, Mr. Kent is trying to learn more about how this super predator lived and died.
Fossils are mineralized remnants or impressions of animals or plants from a past geologic age. The teeth, made of very durable dentine and enamel materials whose pores are full of mineralized materials, are basically all that’s left of these sharks. Their skeletons were made of cartilage that breaks down too quickly for soil sediments around them to harden into stone.
“But teeth can tell us a lot,” Mr. Kent says. “Just by studying teeth we can learn what they ate and how they attacked their prey.”
Stephen Godfrey, curator of paleontology at the Calvert Marine Museum in Solomons, Md., likens the study of fossils (teeth and others) to forensic science, since fossils give us clues as to extinct species’ behavior and appearance.
“When you study shark tooth marks on skeletal remains of other animals, such as whales and porpoises, it tells you that these sharks went for large prey,” Mr. Godfrey says.
One of the reasons researchers can tell that the tooth marks are from sharks is that the serration marks on the prey’s bone and those of the actual shark tooth match perfectly.
Mr. Godfrey and Mr. Kent have found dozens of fossilized giant white and other extinct sharks’ teeth at the Calvert Cliffs over the years. After spring thunderstorms, pieces of the cliffs break off under the pressure from the water. This frees up fossils that have been buried in the cliff.
Another sign that the giant white shark attacked large prey, up to 20 feet long, are the compression fractures on the shark teeth that Mr. Kent and other researchers have found.
“It indicates that they were biting down on large animals’ bones, sending ripples or shock waves through the teeth,” Mr. Kent says.
Animals have different attack strategies depending on the shape of their teeth. A modern great white probably would bite the prey with its razor-sharp — but not very big — teeth and then let the prey bleed to death before devouring it.
The giant white, on the other hand, had such leverage and strength that it probably killed the prey immediately, attacking the animal’s center of mass — the shoulder and torso regions — where all the vital organs were located.
“It probably knocked the air out of the lungs [of the prey], killing it instantly,” Mr. Kent says. “It must have been a gruesome sight.”
The giant white shark not only had huge teeth, but also had four to five rows of them, just like the present-day great white shark.
At the Calvert Marine Museum, visitors can see just how terrifying that looks as the museum features a 37-foot reproduction (which actually is small) of the giant white shark, or carcharodon megalodon, in its shark exhibit.
The exhibit is a visitor favorite, probably because humans are entranced by giant predators, Mr. Godfrey says.
“Just the sheer size of it is impressive,” he says. “People look at it and think, ‘I’m glad it’s not still alive.’ Yet, we’re fascinated by giant predators,” he says.
Studying fossils is one way to try to figure out the giant white shark’s behavior and appearance.
But since a complete giant white shark skeleton has never been found, and probably never will be, researchers must use other methods to paint a more complete picture.
One way is to look at the most similar shark species alive today — the great white shark — and extrapolate information from it.
“You have to look at living species and make inferences,” Mr. Kent says. “But this can be problematic.”
For example, just tripling the size and shape of the current great white and assuming that would create the size and shape of the giant white, probably is not correct, he says. Mr. Kent, who uses mathematical models and engineering principles to understand extinct animals, says that extrapolation would create a shark that wouldn’t move very well in the water.
“It probably was more slender in order to move fast,” he says.
By using biomechanical analysis, Mr. Kent can further back up the theories that the giant white shark ate big prey. He can show the presumed strength and leverage of the jaws by using information from the size of the fossilized teeth and the estimation of the jaw size.
“I use mathematical models to try to figure out what these sharks were probably doing and eating,” Mr. Kent says.
So, why did this super predator die out?
About 2 million years ago, Earth went through a climate change that reduced the upwelling of nutrients from the ocean floor to the surface, Mr. Kent says. This change started wiping out large numbers of whales and porpoises, the giant white’s main food.
The super predator was unable to adapt to the new situation, Mr. Kent says. It couldn’t get enough energy from eating smaller animals to sustain itself. Large carnivores want to eat prey about one-third of their own size to make it worth the energy that the stalking and chasing require.
The great white shark, on the other hand, had more versatility and was able to survive.
But while the 50-ton — the size of six Tyrannosaurus rex — super predator has been gone for 2 million years, people are still interested in it, Mr. Kent says.
“Everybody likes a good monster story,” Mr. Kent says. “And it doesn’t get much better than the giant white shark.”
www.washingtontimes.com/news/2003/jul/16/20030716-094238-4652r/
