Multiple Choice
Plants colonized land in the company of __________; their symbiotic relationships still exist today.
24. History of Life on Earth
History of Life on Earth
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Although they originated around 180 million years ago, mammals underwent an adaptive radiation starting approximately 65 million years ago. Why?
A
Mammals were not well adapted to the climate that existed before about 65 million years ago.
B
Mammals were mostly nocturnal until 65 million years ago.
C
Fur evolved in mammals around 65 million years ago, enabling them to withstand colder temperatures.
D
All of the listed responses are correct.
E
Between 180 and 65 million years ago, mammals were outcompeted by the well-established dinosaurs.
Verified step by step guidance1
Understand the concept of adaptive radiation: Adaptive radiation is the process by which organisms diversify rapidly into a multitude of new forms, particularly when changes in the environment make new resources available, create new challenges, or open new environmental niches.
Consider the timeline: Mammals originated around 180 million years ago but underwent significant adaptive radiation approximately 65 million years ago. This period coincides with the extinction of dinosaurs, which were dominant before this time.
Evaluate the environmental changes: Around 65 million years ago, a mass extinction event occurred, likely due to a catastrophic event such as an asteroid impact. This led to the extinction of dinosaurs, which had previously outcompeted mammals.
Analyze the ecological opportunities: With the extinction of dinosaurs, mammals had the opportunity to occupy ecological niches that were previously dominated by dinosaurs. This allowed mammals to diversify and adapt to various environments.
Conclude the reasoning: The adaptive radiation of mammals was primarily due to the removal of competition from dinosaurs, allowing mammals to explore and adapt to new ecological niches, rather than changes in climate or nocturnal behavior.
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