The Glyptodon, a giant armored mammal that lived during the Pleistocene epoch, has long been considered a purely terrestrial herbivore. However, recent evidence suggests that Glyptodon may have engaged in seasonal migration, much like modern elephants or caribou. Three main arguments support this hypothesis. First, isotopic analysis of Glyptodon fossil teeth reveals variations in carbon and oxygen isotope ratios that correlate with seasonal climate changes, indicating that the animals moved between different vegetation zones. Second, the geographic distribution of Glyptodon fossils spans a wide range of latitudes and altitudes, from lowland grasslands to highland valleys, which would be unnecessary if the species remained in a single habitat year-round. Third, modern relatives of Glyptodon, such as armadillos, are known to undertake short-distance migrations in response to food availability, suggesting that migratory behavior is phylogenetically plausible within this group. Together, these lines of evidence imply that Glyptodon was not sedentary but rather migrated seasonally to exploit resources.
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The professor argues that the migration hypothesis for Glyptodon is flawed. First, the isotopic variations in the teeth do not necessarily indicate movement. These variations could result from dietary shifts, such as eating different plants in the same region during wet and dry seasons, or from physiological changes like lactation or metabolic stress. Without direct evidence of spatial movement, such as matching isotope signatures in teeth to specific geographic locations, the data are inconclusive. Second, the broad fossil distribution does not require migration. Glyptodon lived for over two million years, and during that time, climate change and geological events could have shifted their habitats, causing populations to become isolated and adapt to local conditions. Fossils in different regions may simply represent separate, non-migratory populations that evolved in place. Third, while modern armadillos do migrate short distances, they are much smaller and have higher metabolic rates than Glyptodon, which was the size of a small car. Large body size in extinct mammals is often associated with reduced mobility and lower energy needs, making long-distance migration energetically costly and unlikely. Therefore, the evidence does not support the claim that Glyptodon migrated seasonally.
📝 작문 지시 Summarize the points made in the lecture, being sure to explain how they cast doubt on the specific points made in the reading passage.
📊 TOEFL Integrated Writing Rubric
Content Accuracy: Accurately capture the relationship between lecture and reading
Information Completeness: Cover all key counter-arguments from the lecture
Structure & Coherence: Logical organization and progression
Language Use: Grammar, vocabulary, expression accuracy
Scored 0-30 based on holistic scoring (original 0-5, scaled to 30).
