词 数 317 难度 　　 Scientists have solved the mystery of why the overwhelming majority of mammoth fossils(化石) are male.

　　Much like wild elephants today, young male Ice Age mammoths probably travelled around alone and more often got themselves into risky situations where they were swept into rivers, or fell through ice or into mud, lakes or sinkholes that preserved their bones for thousands of years, scientists say.

　　Females, on the other hand, travelled in groups led by an older matriarch who knew the landscape and directed her group away from danger.

　　"Without the benefit of living in a herd led by an experienced female, male mammoths had a much higher risk of dying in natural traps such as mud holes, rock cracks and lakes，" said co­author Love Dalén of the Swedish Museum of Natural History in a report published on Thursday in the journal Current Biology.

　　The study used genetic data to determine the sex of 98 woolly mammoth fossils in Siberia. Researchers found that 69% of the samples were male, a heavily unbalanced sex ratio, assuming that the sexes were fairly even at birth.

　　"We were very surprised because there was no reason to expect a sex bias in the fossil record，" said first author Patricia Pecnerova, also of the Swedish Museum of Natural History.

　　Therefore, researchers believe that something about the way they lived influenced the way they died.

　　"Most bones, tusks, and teeth from mammoths and other Ice Age animals haven't survived，" explained Dalén.

　　"It is highly likely that the remains that are found in Siberia these days have been preserved because they have been buried, and thus protected from weathering."

　　These giant, tusked plant eaters disappeared about 4,000 years ago. While there is no scientific agreement on the causes of their disappearance from the planet, most believe that climate change, excessive hunting by humans and the spread of other animals into mammoth feeding grounds were influential factors.

　　语篇导读　本文主要介绍了猛犸象化石大多是雄性以及这种生物从地球上最终消失的原因。

　　5．The underlined word "matriarch" in Paragraph 3 means ________.

　　A．figurehead B．female leader

　　C．experienced animal D．mature mammoth

解析　B　词义猜测题。根据第四段中的Without the benefit...natural traps可推知，matriarch是指有经验的雌性领导，故选B项。