开始是一个现象，并且往往很古怪，作者在后面一般会给出合理的解释。
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.
第一段
事实：最新的研究为捕食者-猎物动态关系提供线索。
事实：研究者对比现存食肉动物和古代食肉动物的牙齿破裂。
发现（现象）：已经灭绝的食肉动物牙齿破裂远高于现存食肉动物的牙齿破裂。
第二段
解释-评价：为上述发现寻找可能解释，研究者不考虑人口统计学误差，因为更老的个体并未过分代表化石样本。
解释-评价：研究者拒绝保存误差，因为存在已灭绝的物种，完全没有牙齿破裂。
解释-评价：研究者拒绝地区/地理误差，因为不同地点收集的破裂数据类似。
解释-评价：研究者认为最可能的例子是已经灭绝的和现存的食肉动物的行为差异。
第三段
推断：彻底的尸骨消耗向研究者们暗示，古代的捕食者要么可捕食的猎物少，要么竞争激烈，并且尸骨失窃率高。
