Have you ever wondered how a turtle got its shell? You're not the only one. Paleontologists (古生物学者) have long been confused by the question. But a recently found turtle fossil (化石), the oldest on record, may hold the answer. Researchers report in Nature that the fossil shows shells evolved（进化）as an extension of turtles' backbones and ribs (肋骨).
“The discovery opens a new chapter in the study of the origins and early history of these fascinating reptiles (爬行动物),” says paleontologist Robert Reisz of the University of Toronto.
Scientists have been in the dark until now because all turtle fossils previously discovered had complete shells. (The previously oldest known turtle was discovered in Germany. It dated to about 210 million years ago. ) But this 220 million-year-old fossil is an ancestor of the modern turtle at a stage when its shell was still evolving.
The 40-cm-long fossil was discovered in Guizhou province. An international team of paleontologists led by Li Chun of the Chinese Academy of Sciences in Beijing analyzed it. They reported that the bones belonged to a Triassic (三叠纪的) turtle, which they named odontochelys semitestacea（半甲齿龟）, meaning “toothed turtle with a half shell”.
The fossil has a shelled belly（腹部）and a little extra bone on its spine (脊柱). That supports the theory that turtles' shells formed over time as their backbones and ribs grew. Before the discovery, some paleontologists thought shells were formed as hard, bony plates in turtles' skin, such as those in the skin of modern-day crocodiles. The authors say that this turtle species probably lived in water and that their stomach shell kept them safe from predators (捕食者) below while they were swimming.
66. The passage is mainly about _______.
A. a brief introduction to the structure of turtle shells
B. a new insight about how turtle shells formed gradually
C. a brief introduction to the living habits of turtles
D. The study of the origins and early history of turtles
67. Which is TRUE about the newly found turtle fossil?
A. It was Li Chun, one Chinese paleontologist, who found the turtle fossil.
B. The turtle fossil found in southwestern China is 210 million years old.
C. The fossil shows turtle shells evolved from turtles' backbones and bellies.
D. Scientists now know how turtle shells evolved with the help of the fossil.
68. What can we conclude from the passage?
A. The newly found fossil plays a key role in studying the origins of reptiles.
B. Paleontologists think turtle shells developed from turtles' hard skin.
C. Some species of turtles don't have stomach shells because they live on land
D. Paleontologists have long been puzzled about what makes up turtle shells.
69. Nature, mentioned in Paragraph 1, is most probably the name of _______.
A. a science fiction B. a magazine on science
C. a photo website D. a science organization
70. The structure of this passage is _______.
① The new theory is very important. ② The oldest turtle fossil was found.
③ A new discovery on how shells evolved has been made.
④ How scientists made a new theory on how shells evolved from the fossil
A. ① ② ③ ④ B. ① ③ ④ ② C. ③ ① ② ④ D. ② ④ ① ③