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Why did sea monsters have long necks?

From the journal Science: A recently found fossil represents a new species of ancient marine reptile, and researchers think its long neck may have helped it hunt prey stealthily.
An artist's rendition shows Dinocephalosaurus orientalis, a long-necked sea reptile that probably preyed on fish and squid in a shallow sea in present-day southeast China more than 230 million years ago. The tail and soft tissues shown here, including the muscles, are a matter of conjecture.
An artist's rendition shows Dinocephalosaurus orientalis, a long-necked sea reptile that probably preyed on fish and squid in a shallow sea in present-day southeast China more than 230 million years ago. The tail and soft tissues shown here, including the muscles, are a matter of conjecture.Illustration: Carin L. Cain / AAAS / Science
/ Source: Science

Scientists working in China have discovered an ancient swimming predator with a neck nearly twice as long as its body. Neck ribs line the reptile’s 5.5-foot-long (1.7-meter-long) neck and may have helped the creature hunt.

The scientists describe the new predator in Friday's issue of the journal Science, published by AAAS, the nonprofit science society.

Some aspects of the animal’s life are relatively easy to reconstruct: It probably ate fish and squid, and lived in a shallow sea more than 230 million years ago. The biggest remaining question about this animal is what purpose such a long neck served.

With bones but no muscles to guide them, the scientists say that it’s hard to be absolutely certain about how the creature used its neck. They have some ideas, however, that relate to hunting.

Terrible-headed lizard
The new creature, Dinocephalosaurus orientalis or “terrible-headed lizard from the Orient,” is the first fully marine member of a diverse reptile group called the protorosaurs. These reptiles are grouped together based on their long necks and elongated neck vertebrae. Their riblike bones extended parallel to the neck vertebrae and restricted neck movement, like straws that are slid down the neck of a turtleneck sweater.

Charles Cockell

Science author Chun Li from the Chinese Academy of Sciences in Beijing discovered the reptile in the autumn of 2002, in the Guanling Formation in China’s Guizhou Province.

The scientists compared this new creature to the famous long-necked reptiles and fellow protorosaurs from Europe and the Middle East called Tanystropheus. This comparison offers new insights into the ways protorosaurs hunted, as well as how they evolved and diversified during the Triassic Period.

While analyzing the new skeleton, Michael LaBarbera, a Science author from the University of Chicago, said he felt Mother Nature directing him to an interesting mystery: The existing explanations for why reptiles have long necks didn’t seem to fit this new predator.

One of the ways the researchers tried to understand the purpose of the new creature’s neck was to look at the long necks of its relatives, like Tanystropheus.

The vertebrae in the necks of Tanystropheus fossils were longer than those in the newly discovered predator. With fewer vertebrae per meter, Tanystropheus necks were probably less flexible than the new reptile’s, in the way that a giraffe’s neck is less flexible than the neck of a heron. The scientists concluded that the necks from these two branches of the protorosaur family tree evolved separately and may have served different functions.

Underwater hunting
To try to make sense of the reptile’s “ridiculous body proportions,” Science author Olivier Rieppel from Chicago's Field Museum and his colleagues considered suction feeding, an underwater hunting strategy commonly used by many of today’s fish and turtles. Fish and turtles drop the floors of their specially designed mouths, increasing volume and decreasing pressure inside their throats. This pressure drop creates a suction force that causes nearby water (and the potential meal swimming in that water) to flow into the predator’s mouth and throat.

If the new reptile’s neck ribs moved the way the scientists propose, the pliable neck ribs might have pushed on the tissue of the throat and expanded the throat enough to create suction.

The scientists suggest that this suction might have allowed the reptile to swallow invisible pressure waves it created as it lunged forward in the water to try to catch a meal. This move would prevent the waves from alerting the fish or squid to the reptile’s approach.

Without information on how the creature’s muscles attached to the bones, other underwater hunting strategies are also possible.

In a complementary scenario, the sheer length of the neck could have helped the reptile in murky waters near the shore. The long neck placed the reptile’s brain, mouth and sensory organs well in front of its body. This neck design could have made it hard for a fish to see the larger body at the other end of the neck. With this threatening profile hidden, the reptile might have been able to move into striking distance before the fish got scared and swam away.

Follow-up in a fish tank
With multiple explanations for the reptile’s long neck and no solid conclusions, the researchers are anxious to find a fossil that tells the story of the reptile’s muscles.

In the meantime, LaBarbera said he might do some experiments in his giant fish tank to try to answer the question, “Is a predator with a long neck better equipped to sneak up on fish than a predator with a short neck?”

He is thinking about submerging predator models with different head shapes and neck lengths in his 90-foot-long, 6-foot-deep, 3-foot-wide (27-by-1.8-by-0.9-meter) glass-walled tank after filling it with goldfish.

He could tow the different models at a fixed speed and monitor the reaction of the fish. He would like to know if head shape or neck length changes the prey-alerting pressure waves the models generate, as he and his colleagues predict.

Neck numbers
While scientists can not yet say for sure exactly how the reptile used its neck, they are sure its long neck was made of 25 elongated neck or “cervical” vertebrae.

Humans have only seven cervical vertebrae and no neck ribs. Our first neck vertebra, atlas, begins at the base of the skull. Reach back and feel the bump at the base of the back of your neck; that’s your seventh and final cervical vertebra, “C7.”

If a 6-foot-tall (1.8-meter-tall) person had the same neck-to-body proportions as Dinocephalosaurus, her neck would be approximately 10 feet (3 meters) long.