Pre-Dinosaur Reptile Discovered -- Long-Necked Hunter
for National Geographic News
|September 23, 2004|
With its body obscured by murky waters, an ancient fanged reptile may have used its long neck to lunge at fish and squid. The scenario is based on analysis of a 230-million-year-old fossil discovered in southeastern China.
The new creature appeared long before the dinosaurs and is named Dinocephalosaurus orientalis, which means "terrible headed lizard from the Orient." It was a protorosaur, part of an order of diverse, predatory reptiles that lived as far back as 280 million years ago.
The ancient reptile had short and broad limbs with relatively few bones in the wrist and ankle joints, an indication that it was more adapted to an aquatic lifestyle than other protorosaurs. (Scientists say living aquatic reptiles may have fewer bones in wrists and ankles than their terrestrial counterparts.)
Dinocephalosaurus also had a relatively stiff neck that was about 5.5 feet (1.7 meters) long. That's nearly twice as long as its trunk, which was three feet (one meter) long. Several thin and flexible rib bones, called cervical ribs, ran along the neck portion of the creature's spine, each bridging several of its 25 neck vertebrae.
"Protorosaurs as a group all have at least somewhat elongated neck vertebrae," said Olivier Rieppel, curator of fossil amphibians and reptiles at the Field Museum in Chicago. Rieppel is co-author of the paper that describes the fossil, which appears in tomorrow's issue of the journal Science.
His past research projects have been funded, in part, by grants from the National Geographic Society's Committee for Research and Exploration.
For years scientists have struggled to explain the functional significance of the elongated necks common to these reptiles. Analysis of the new fossil by Rieppel and his colleagues offers a solution to the enigma: The feature may have helped protorosaurs hunt.
The mystery surrounding the protorosaurian neck dates back to Tanystropheus longobardicus, a protorosaur from Europe and the Middle East discovered in the 1850s.
Tanystropheus had 12 "grotesquely elongated" neck vertebrae. Scientists could only explain then as a consequence of growth patterns but not as serving any specific purpose, Rieppel said. As in Dinocephalosaurus, cervical ribs in Tanystropheus bridged multiple vertebrae.
After comparing the Dinocephalosaurus fossil to living animals and thinking about how the creature fed in murky coastal waters, Rieppel and his colleagues believe they have discovered a more specific function for the elongated necks.
At the very least, the authors say, the elongated neck would have allowed the reptile to sneak up and lunge at its prey in murky waters close to shorebefore the creature's full profile scared off a potential meal.
Michael LaBarbera, a study co-author and an organismal biologist at the University of Chicago, suggested a second hunting strategy that employs the neck ribs.
According to LaBarbera, contraction of Dinocephalosaurus's neck muscles would create a rapid straightening of the neck, thrusting the head toward the prey. At the same time the neck ribs would have splayed outward, increasing the volume of the esophagus.
This increased volume is important, according to the researchers. It would have created a suction force that allowed Dinocephalosaurus to swallow the pressure wave that was created as the reptile lunged its head forward through the water.
Pressure waves can serve as a warning signal to prey. Several animals employ strategies to swallow these waves in order to attack more stealthily. Dinocephalosaurus, according to the researchers, was no different.
"Looking back at Tanystropheus, it probably had the same mechanism, but the mechanism was not recognized by scientists," Rieppel said.
Hans-Dieter Sues, the associate director for research and collections at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., voiced caution about this interpretation. His doubts are based on his own examination of Tanystropheus neck vertebrae.
"The cervical ribs of tanystropheid reptiles are very long, spanning multiple vertebrae. I think that, because of these ribs, the neck would have always been held fairly straight, with quite limited side-to-side and even less up-and-down mobility," he said.
Sues, who is a member of the National Geographic Society's Committee for Research and Exploration, added that the neck ribs may have splayed a little; most vertebrates that feed underwater incorporate some suction in capturing prey.
The lead author of the paper, Chun Li of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences in Beijing, discovered Dinocephalosaurus in 2002.
He had been looking for a protorosaurian in southern China for three years, with no luck. Back in a local village after another disappointing day in the field, he was told about some "coarse bones" in limestone a farmer had dug up for use as cement.
"Although the farmer misunderstood the extremely long neck of the monster as its tail, as most people would do, I knew that it was the long-necked protorosaur, which I had searched for for more than three years," Li said.
He added, "I realized that new and different information would be known from this specimen, although I didn't know what at that moment."
According to Sues, reconstructions of well-preserved protorosaurian neck vertebrae are needed to fully understand the biomechanics of the creatures' elongated necks. Such reconstructions do not yet exist.
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