The strike would have come out of nowhere: One second the fish was swimming placidly, no danger in sight, a moment later it was lunch.

Scientists have discovered what may have been one of the first stealth hunters, a long-necked swimming dinosaur that could sneak up on prey and attack without warning.

"The long neck would allow it to approach prey without the whole body becoming visible," Olivier Rieppel of the Field Museum (search) in Chicago, a co-author of the report, said in a telephone interview.

The newly found reptile with fangs lived in a shallow sea in what is now southeast China more than 230 million years ago, the research team, led by Chun Li of the Chinese Academy of Sciences (search), reports in Thursday's issue of the journal Science.

Li first found the head of the dinosaur in the fall of 2002, and later uncovered the remainder of the animal. He named it Dinocephalosaurus orientalis (search), meaning terrible headed lizard from the Orient.

Dinocephalosaurus — with a body about three feet long and a neck adding five and a half feet — is related to Tanystropheus, another long-necked reptile that lived in the area of Europe and the Middle East.

But the researchers said the newly named creature had 25 neck vertebrae, more than twice that of Tanystropheus, and in Dinocephalosaurus they were not as elongated. It had rib-like bones parallel to the vertebrae.

Both are members of a diverse reptile group called the protorosaurs (search), which have long necks and elongated neck vertebrae.

Scientists have long wondered at the purpose for the long necks in this group of animals.

"This is important research because we have finally explained the functional purpose of this strange, long neck," said Rieppel, head of geology and curator of fossil amphibians and reptiles at the Field Museum.

As Dinocephalosaurus approached in murky water, its prey would have been aware only of the relatively small head, not the full-size profile of a predator.

Michael LaBarbera of the University of Chicago, a co-author of the report, said the rib-like bones along the side of the neck may also have played a role in hunting.

Those bones give the neck some stiffness, Rieppel explained. It could flex, but not like a snake.

According to LaBarbera, contraction of the creature's neck muscles could have rapidly straightened the neck and splayed the neck ribs outward.

That would have greatly increased the volume of the throat, allowing the animal to lunge forward in the water at prey.

Ordinarily, lunging through water creates a pressure wave that a fish can sense, allowing it to flee. But the researchers said that by suddenly enlarging its throat Dinocephalosaurus could, in effect, suck in and swallow its own pressure wave, giving it the ability to strike without warning.

"It allowed an almost perfect strike at prey, which usually consisted of elusive fish and squid," Rieppel said.

It's a process similar to the suction feeding done by some fish and turtles, Rieppel added.

"Feeding underwater in a dense medium is always a problem, and suction feeding is an elegant solution," he said.

But, LaBarbera said in a statement, "suction feeding in Dinocephalosaurus was different from suction feeding in any other animal. Rather than expand the volume of its mouth to suck in prey, Dinocephalosaurus expanded the volume of its throat, in many ways a more effective approach."

The research was funded by the National Natural Science Foundation of China.