Passage 37
A recent study has provided clues to predator-prey1 dynamics2 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 bias3
because older inpiduals 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 abrasion5 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 plausible6 is behavioral differences between extinct and present-day
carnivores-in particular, more contact between the teeth of predators7 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 seasonally8, or
that there was intense competition over kills and a high rate of carcass theft due to relatively9 high
predator densities10.
231. The primary purpose of the passage is to
present several explanations for a well-known fact
suggest alternative method of resolving a debate
argue in favor of a controversial theory
question the methodology used in a study
discuss the implications of a research finding
232. The passage suggests that, compared with Pleistocene carnivores in other areas, Pleistocene
carnivores in the La Brea area
included the same species, in approximately the same proportions
had a similar frequency of tooth fractures
populated the La Brea more densely
consumed their preys11 more thoroughly12
found it harder to obtain sufficiency prey
233. According to the passage, the researchers believes that the high frequency of tooth breakage
in carnivores found at La Brea was caused primarily by
the aging process in inpidual carnivores
contact between the fossils in the pits
poor preservation4 of the fossils after they wer removed from the pits
the impact of carnivores teeth against the bones of their prey
the impact of carnivores teeth against the bones of other carnivores during fights over kills
234. The researchers conclusion concerning the absence of demographic bias would be most
seriously undermined if it were found that
the older as inpidual carnivore is, the more likely it is to have a large number of tooth fratures
the average age at death of a present-day carnivores is greater than was the average age at death of a Pleistocene carnivore
in Pleistocene carnivore species, older inpiduals consumed carcasses as thoroughly as idd younger inpiduals
the methods used to determine animals ages in fossile samples tend to misidentify many older inpiduals as younger inpiduals
data concerning the ages of fossil samples cannot provide reliable information about behavioral differences between extinct carnivores and present-day carnivores
235. The passage suggests that 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 fossile remains13 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 carcass
all Pleistocene carnivores species differed behaviorally from present-day carnivore species.
predator desities during the Pleistocene era were extremely high
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