Chinese scientists have discovered the oldest known turtle fossils and revealed the origin of the turtle's shell. This discovery was reported in the latest issue of Nature.
Nature says that the discovery opens up a completely new path in the research of reptile evolution, and will force scientists to rethink the origins of the turtle.
The fossils were found in sediments deposited in Guanling Buyi-Miao Autonomous County, Guizhou Province, 220 million years ago. Because the specimen has dense teeth and primitive embryonic shell, scientists named it Odontochelys semitestacea.
According to Li Chun of the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences, fossil turtle specimens are extremely rare. Just three primitive turtle specimens have been found – in Germany, Thailand and Argentina – but their body structures are very similar to today's turtle, so give few clues as to the creature's origins.
Astonishingly, this Chinese specimen has a fully developed plastron – the flat underside of the shell. Its body structure suggests that the plastron was formed earlier than the carapace – the upper, dorsal part, and that the two sections of the shell evolved separately. What's more, the carapace grew from vertebra, which contradicts the prevailing hypothesis that the shell was formed by bony deposits fusing together.
The origin of turtles turns out to be more complex than had been thought. Many scientists had believed turtles evolved on land but the bone structure of Odontochelys semitestacea and the geological conditions of its location strongly suggest turtles originated in water.
This research was supported by the Chinese Academy of Sciences, the National Natural Science Foundation of China, and the 973 Program of the Ministry of Science and Technology. Professor Wang Liting from Guizhou Institute of Geological Survey, and Zhao Lijun from Zhejiang Museum of Natural History contributed to this discovery, along with experts from Canada and the United States.
(China.org.cn by Fan Junmei, November 28, 2008)