(Q001) Watch the animation "Primate Migration" and answer the question that follows.
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Why is it unlikely that platyrrhine ancestors migrated from North America and evolved into the platyrrhine species of the Oligocene?

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(Q001) Watch the animation "Primate Migration" and answer the question that follows.
https://util.wwnorton.com/jwplayer?type=video&msrc=/wwnorton.college.protected/coursepacks/phys_anthro/animations/animation_primate_migration.mp4&isrc=/wwnorton.college.protected/coursepacks/phys_anthro/animations/animation_primate_migration.jpg&csrc=/wwnorton.college.protected/coursepacks/phys_anthro/animations/animation_primate_migration.vtt&cp=1

Why is it unlikely that platyrrhine ancestors migrated from North America and evolved into the platyrrhine species of the Oligocene?

BlackTom AI · Accepted Answer

The question asks why it is unlikely that platyrrhine ancestors migrated from North America and evolved into the platyrrhine species of the Oligocene.

First, note that the answer options are not listed in the provided data beyond a single option: 'There is no evidence that there were anthropoids in North or South America during the Eocene or Oligocene.' There are no alternative choices to compare, so we cannot evaluate multiple competing explanations. This means we must focus on the single stated option and consider its validity in light of known paleontological context.

Option provided: 'There is no evidence that there were anthropoids in North or South America during the Eocene or Oligocene.' This claim implies that anthropoids (the group that includes platyrrhines) did not occur in the American continents during those epochs, which would make migration and subsequent evolution into the Oligocene platyrrhine line improbable. The reasoning behind this statement rests on the fossil record and biogeographic history:
- Fossil evidence: If there were anthropoid fossils in North or South America dating to the Eocene or Oligocene, that would support potential migration events. The absence of such fossil evidence suggests that migration did not occur or is not well supported by fossils from that time.
- Biogeography: The geographic barriers (oceans and climate) between Africa/Asia and the Americas and the timing of faunal dispersals are important. Platyrrhines are traditionally believed to have originated in South America, with their appearance in the Oligocene indicating a later dispersal event, potentially via rafting or other means from Africa via the Caribbean region. A lack of evidence for anthropoids in North/South America during the Eocene/Oligocene would argue against early migrations from North America as sources of platyrrhines.
- Dating and correlation: The Eocene (about 56–34 million years ago) and Oligocene (about 34–23 million years ago) timeframes are when primates were diversifying. If anthropoids were absent from the continents during these times, it reduces plausibility of a North American origin for later South American platyrrhines.

However, to fully assess this option, one might also consider counterpoints such as potential gaps in the fossil record, re-interpretations of fragmentary remains, or alternative dispersal scenarios (e.g., southward dispersal from Africa to South America via transient land connections or island chains that could have been missed in the record). The absence of evidence is not always definitive proof of absence, but for this question, the statement aligns with the conventional narrative that there is no solid fossil support for anthropoids in the Americas during those periods, making a North American origin unlikely.

In sum, given the single option provided, the reasoning supports why such a migration is considered unlikely: the fossil record shows no evidence of anthropoids in North or South America during the Eocene/Oligocene, making a North American origin for later platyrrhines improbable based on available data. If there were additional options, we would compare them similarly by weighing fossil evidence, timing, and biogeographic plausibility to determine which reasoning is best supported by the data.

ANTH-101-03 CH 09 ANIMATION EXERCISE: Primate Migration

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