A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in present-day carnivores with tooth fractures in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.

In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.

The passage suggests that tooth fractures in Pleistocene carnivores probably tended to occur less frequently

during periods in which more prey were available

at sites distant from the La Brea area

in older individual carnivores

in species that were not preserved as fossils

in species that regularly stole carcasses from other species







这个题目定位在文章的最后部分内容中。作者在这部分内容中的意思是,牙齿的破坏实际上是因为捕猎者牙齿与猎物的骨骼接触所造成的。有可能有两个原因造成了这样的情况----猎物过少或尸体被偷(捕猎者过多)。注意题目问的是“less frequently”。


A选项:Correct. 在有更多的猎物的时期。有了更多的猎物,捕食者就不用和尸体的骨骼打交道了。所以牙齿的磨损就少了。

B选项:在远离La Brea的地区。作者在前文中已经批驳了“local bias”。地域性和牙齿的磨损程度没有关系。



在习惯性的偷盗其他物种的尸体的种群中。这个选项说反了。偷盗尸体意味着食用尸体,进而牙齿与骨骼更多的接触,导致牙齿更多的损坏。注意题目问的是“less frequently”。


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