Prehistoric shark hid its largest teeth

November 18, 2020

Some, if not all, early sharks that lived 300 to 400 million years ago not only dropped their lower jaws downward but rotated them outwards when opening their mouths. This enabled them to make the best of their largest, sharpest and inward-facing teeth when catching prey, paleontologists at the Universities of Zurich and Chicago have now shown using CT scanning and 3D printing.

Many modern sharks have row upon row of formidable sharp teeth that constantly regrow and can easily be seen if their mouths are just slightly opened. But this was not always the case. The teeth in the ancestors of today's cartilaginous fish (chondrichthyan), which include sharks, rays and chimaeras, were replaced more slowly. With mouths closed, the older, smaller and worn out teeth of sharks stood upright on the jaw, while the younger and larger teeth pointed towards the tongue and were thus invisible when the mouth was closed.

Jaw reconstruction thanks to computed tomography

Paleontologists at the University of Zurich, the University of Chicago and the Naturalis Biodiversity Center in Leiden (Netherlands) have now examined the structure and function of this peculiar jaw construction based on a 370-million-year-old chondrichthyan from Morocco. Using computed tomography scans, the researchers were able not only to reconstruct the jaw, but also print it out as a 3D model. This enabled them to simulate and test the jaw's mechanics.

What they discovered in the process was that unlike in humans, the two sides of the lower jaw were not fused in the middle. This enabled the animals to not only drop the jaw halves downward but at the same automatically rotate both outwards. "Through this rotation, the younger, larger and sharper teeth, which usually pointed toward the inside of the mouth, were brought into an upright position. This made it easier for animals to impale their prey," explains first author Linda Frey. "Through an inward rotation, the teeth then pushed the prey deeper into the buccal space when the jaws closed."

Jaw joint widespread in the Paleozoic era

This mechanism not only made sure the larger, inward-facing teeth were used, but also enabled the animals to engage in what is known as suction-feeding. "In combination with the outward movement, the opening of the jaws causes sea water to rush into the oral cavity, while closing them results in a mechanical pull that entraps and immobilizes the prey."

Since cartilaginous skeletons are barely mineralized and generally not that well preserved as fossils, this jaw construction has evaded researchers for a long time. "The excellently preserved fossil we've examined is a unique specimen," says UZH paleontologist and last author Christian Klug. He and his team believe that the described type of jaw joint played an important role in the Paleozoic era. With increasingly frequent tooth replacement, however, it became obsolete over time and was replaced by the often peculiar and more complex jaws of modern-day sharks and rays.
-end-


University of Zurich

Related Teeth Articles from Brightsurf:

Astronomers sink their teeth into special supernova
Astronomers using several telescopes at NOIRLab, including the Southern Astrophysical Research (SOAR) Telescope, have obtained critical data on a particular type of exploding star that produces copious amounts of calcium.

Researchers discover biomarkers of ALS in teeth
Mount Sinai scientists have identified biological markers present in childhood that relate to the degenerative and often fatal neurological disease called amyotrophic lateral sclerosis, also known as ALS or Lou Gehrig's disease, according to a study published in the Annals of Clinical and Translational Neurology in May.

Brush your teeth to protect the heart
Brushing teeth frequently is linked with lower risks of atrial fibrillation and heart failure, according to a study published today in the European Journal of Preventive Cardiology, a journal of the European Society of Cardiology (ESC).

Piranha fish swap old teeth for new simultaneously
With the help of new technologies, a team led by the University of Washington has confirmed that piranhas lose and regrow all the teeth on one side of their face multiple times throughout their lives.

What wolves' teeth reveal about their lives
UCLA biologist discovers what wolves' broken teeth reveal about their lives.

These pink sea urchins have teeth that sharpen themselves
Sea urchins have five teeth, each held by a separate jaw in a circular arrangement at the center of their spiked, spherical bodies.

The secret strength of gnashing teeth
There's a method to finite element modeling for materials microarchitecture to make super strong glass.

No teeth cleaning needed: Crocodiles shed old teeth, grow new ones
Having one of the most powerful bites in the animal kingdom, crocodiles must be able to bite hard to eat their food such as turtles, wildebeest and other large prey.

Why deep-sea dragonfish have transparent teeth
Off the coast of San Diego, 500 meters under the sea, pencil-sized sea monsters grin pitch-black smiles because their mouths are filled with transparent teeth.

Brush your teeth -- postpone Alzheimer's
Researchers at the University of Bergen in Norway have discovered a clear connection between oral health and Alzheimer┬┤s disease.

Read More: Teeth News and Teeth Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.