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.


According to the passage, if the researchers had NOT found that two extinct carnivore species were free of tooth breakage, the researchers would have concluded that


the difference in breakage frequencies could have been the result of damage to the fossil remains in the La Brea pits

the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits

Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcasses

all Pleistocene carnivore species differed behaviorally from present-day carnivore species

predator densities during the Pleistocene era were extremely high

考题讲解

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正确答案是 A。

在文中,研究人员考虑了一些可能的解释来解释这一发现,包括人口偏差,保存偏差和当地偏差。由于他们发现两种灭绝的食肉动物物种没有齿痕损坏,因此他们排除了保存偏差这一可能性。如果这些研究人员没有发现两种灭绝的食肉动物没有牙齿损坏,他们就会得出结论,即差异可能是由于拉布雷亚泥坑中化石需要经历的损坏而导致的。

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