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 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 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
(A)   present several explanations for a well-known fact
(B)    suggest alternative method of resolving a debate
(C)    argue in favor of a controversial theory
(D)    question the methodology used in a study (E)
(E)     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
(A)   included the same species, in approximately the same proportions
(B)    had a similar frequency of tooth fractures
(C)    populated the La Brea more densely
(D)    consumed their preys¹¹ more thoroughly¹² (B)
(E)     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
(A)   the aging process in individual carnivores
(B)    contact between the fossils in the pits
(C)    poor preservation⁴ of the fossils after they wer removed from the pits
(D)    the impact of carnivores’ teeth against the bones of their prey (D)
(E)     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
(A)   the older as individual carnivore is, the more likely it is to have a large number of tooth fratures
(B)    the average age at death of a present-day carnivores is greater than was the average age at death of a Pleistocene carnivore
(C)    in Pleistocene carnivore species, older individuals consumed carcasses as thoroughly as idd younger individuals
(D)    the methods used to determine animals’ ages in fossile samples tend to misidentify many older individuals as younger individuals (D)
(E)     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
(A)   the difference in breakage frequencies could have been the result of damage to the fossile remains¹³ in the La Brea pits
(B)    the fossils in other Pleistocene sites could have higher breakage frequencies than do the fossils in the La Brea pits
(C)    Pleistocene carnivore species probably behaved very similarly to one another with respect to consumption of carcass
(D)    all Pleistocene carnivores species differed behaviorally from present-day carnivore species. (A)
(E)     predator desities during the Pleistocene era were extremely high

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