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Mystery from the deep creates puzzle
Protorosaurs are a group of carnivorous (meat-eating) reptiles who lived in the Triassic Period about 206-248 million years ago.
It is the first time a protorosaur has been discovered in China, says Li Chun, the lead author of the article. The strange long-necked fossil creature, named Dinocephalosaurus orientalis, has not been found anywhere else in the world, says the researcher with the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences. Two fossil specimens of the protorosaur were found in a marine limestone formation dating back to the Middle Triassic Period (230 million years ago) near Xinmin of Guizhou Province in 2002 and collected by the institute. One is the reptile's skull and neck fossil and another is its trunk. "They have been the only fossil evidence of the creature we've got so far," Li says. Xu has studied the specimens and completed the article in co-operation with Olivier Rieppel from the Field Museum in Chicago and Michael C. LaBarbera from the University of Chicago. They found the protorosaur, which has a 1.7-metre-long neck and a trunk less than 1 metre long, was a marine species. "So it is unlike most protorosaurs which were living on land," says Li. According to him, neck elongation is a derived character of protorosaurs. Dinocephalosaurus share additional diagnostic characters with the other protorosaurs, such as elongated cervical ribs and very low neural spines on the neck vertebrae. But its limbs indicate full marine habits - and different from all the other protorosaurs, which retain juvenile characteristics throughout adulthood, they are relatively short and broad. Also, the researchers say although the fossil reptile has a long neck similar to the giraffe-necked protorosaur Tanystropheus found in Europe, its strange form evolved from an adaption mechanism different from the one that created its European relative. According to the article, the neck of Guizhou's Dinocephalosaurus incorporates 25 elongated vertebrae while Tanystropheus in Europe has 12. Tanystropheus adopted an extreme "giraffe-neck" developmental programme with only a moderate increase in the number of cervical vertebrae. Dinocephalosaurus shows a lesser elongation of individual neck vertebrae but an increase in their number. "That means the elongation of the neck is only convergent in the two species," Lu says. Through research, the paleontologists also disclosed the unique hunting method of the strange creature. As its slender neck positions the head well in front of the sturdy body, it could closely approach potential prey even before its target could make out the profile of the predator in dimly-lit waters. Given the length and slenderness of the cervical ribs, the strange protorosaur was very flexible. Contraction of muscles and bridging the intervertebral joints would enable it to rapidly straighten its neck, while the ribs would simultaneously splay outward. The consequent increase of the esophageal volume would create suction such that the animal would essentially swallow the pressure wave created as its head lunged forward. This would result in an almost perfect strike at prey in water. Similar to crocodiles, the fossil shows concave-convex dental margins with fang-like teeth on both upper and lower jaws. The tooth arrangement would have helped the animal to secure its prey once caught. According to Li, his research was supported by National Natural Science Foundation of China. During the past five years, the foundation has supported researchers to make field studies which have harvested a large amount of valuable fossil specimens from the Triassic Period. Many fossilized animals were found first in the country and Asia. "We need more time to unveil the secrets hidden in them," he says.
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