Although many lines of evidence indicate that birds evolved from ground-dwelling theropod dinosaurs, some scientists remain unconvinced. They argue that theropods appeared too late to have given rise to birds, noting that Archaeopteryx lithographica – the oldest known bird – appears in the fossil record about 150 million years ago, whereas the fossil remains of various nonavian maniraptor theropods – the closest known relatives of birds – date only to about 115 million years ago. But investigators have now uncovered bones that evidently belong to nonavian maniraptors dating to the time of Archaeopteryx. In any case, failure to find fossils of a predicted kind does not rule out their existence in an undiscovered deposit. Skeptics also argue that the fused clavicles (the “wishbone”) of birds differ from the unfused clavicles of theropods. This objection was reasonable when only early theropod clavicles had been discovered, but fossilized theropod clavicles that look just like the wishbone of Archaeopteryx have now been unearthed. Finally, some scientists argue that the complex lungs of birds could not have evolved from theropod lungs, an assertion that cannot be supported or falsified at the moment, because no fossil lungs are preserved in the paleontological record.
Q7 Which of the following is mentioned in the passage as an argument made by scientists who are unconvinced that birds evolved from theropod dinosaurs? A. There are no known theropod dinosaur fossils dating from a period after the time of Archaeopteryx. B. There are no known theropod dinosaur fossils that indicate the structure of those dinosaurs’ lungs. C. Theropod dinosaurs appear in the fossil record about 150 million years ago. D. Theropod dinosaurs did not have fused clavicles. E.Theropod dinosaurs had certain bones that look just like those of Archaeopteryx.
京公网安备11010202008513号 京ICP证101109号 京ICP备12012021号
发表于 2010-8-2 15:41:08
收藏
收藏
楼主
