February 27, 2013
Mystery Of The 25-Foot Ancient Spiral-Toothed Shark Solved?
Brett Smith for redOrbit.com - Your Universe Online
Imagine a 25-foot-long shark, but instead of having a typical set of jaws, it packs a chainsaw-like ℠tongue´ full of razor-sharp teeth ready to slash through prey with ease.
While it sounds like something straight out of a Killer B Movie, it is anything but.
A group of American researchers has described just such a creature that lived about 270 million years ago based on the animal´s fossilized spiral set of teeth.
According to their report in the journal Biology Letters, the research team used CT scans and computer modeling to recreate the ancient predator, which once inhabited the waters around modern-day Idaho.
Known as a Helicoprion, the fish is probably more closely related to modern chimeras, or ratfish, than today´s sharks. Since their skeletons were mostly cartilage, the fossil record of the fish is quite limited.
The most prevalent fossil is also the Helicoprion´s most notable feature — its spiral set of teeth known as a ℠whorl.´ These structures have fascinated paleontologists for decades, but the scientific community had never pieced together how the structure fit into the animal´s physiology.
"We were able to answer where the set of teeth fit in the animal," said the study´s lead author Leif Tapanila, a natural history professor at Idaho State University's [ISU] Earth Sciences Division. "They fit in the back of the mouth, right next to the back joint of the jaw. We were able to refute that it might have been located at the front of the jaw."
To reconstruct the ancient beast, the team used the most complete whorl fossil in their collection. Discovered in Idaho, the fossil measures 9 inches, contains 117 individual teeth and includes impressions of the cartilage that held the structure in place. The researchers were able to analyze deep inside the fossil using CT scans.
"When we got the images back, we could easily see that we had the upper and lower jaw of the animals, as well as the spiral of teeth," Tapanila told BBC Nature. "For the first time we were able to very clearly image how that spiral of teeth relates to the jaw."
Tapanila said try to imagine having a spiral set of teeth attached to the back of your lower jaw.
"Only maybe a dozen teeth are poking up out of your lower jaw so you can bite,” he said. "The rest of those teeth are stored inside and are not being used, those are your baby teeth - the teeth you had when you were younger."
The team then used 3-D computer modeling to illustrate how the jaw might have been used.
"As the mouth closes, the teeth spin backwards... so they slash through the meat that they are biting into," Tapanila said. "The teeth themselves are very narrow: nice long, pointy, triangular teeth with serrations like a steak knife.”
"As the jaw is closing and the teeth are spinning past whatever it's eating, it's making a very nice clean cut,” he added.
Based on the condition of the teeth fossils, the team also concluded that the Helicoprion probably ate soft-bodied fish and avoided ancient turtle or shellfish.
"If this animal were eating other animals that were very hard or [had] hard armor plating or dense shells, you would expect more damage to their teeth,” Tapanila said. "This leads us to believe that our animal was probably eating soft, squishy things like calamari. It was probably eating squid or its relatives that were swimming in the ocean at the time."