Question

Examine the data from the fossil record shown here. Which of these statements explains why the diversity of mammals increased exponentially after 65 million years ago?
Responses
A The increased ionizing radiation in the atmosphere increased the photosynthesis and food availability for mammals.The increased ionizing radiation in the atmosphere increased the photosynthesis and food availability for mammals.
B The increased temperatures on Earth provided the ability for mammals to have increased metabolism and survival.The increased temperatures on Earth provided the ability for mammals to have increased metabolism and survival.
C The shrinking of the oceans likely left more exposed land on which mammals diversified.The shrinking of the oceans likely left more exposed land on which mammals diversified.
D The extinction of the dinosaurs 65 million years ago left unfilled niches for mammals.

Answer 1

The best explanation for the increase in mammalian diversity after 65 million years ago is:

**D**: The extinction of the dinosaurs 65 million years ago left unfilled niches for mammals.

This event, often attributed to a mass extinction caused by a significant asteroid impact, removed many dominant species and opened up various ecological niches. Mammals, which were previously smaller and less diverse, had the opportunity to evolve and diversify into the spaces left vacant by dinosaurs, leading to the exponential increase in mammal diversity observed in the fossil record after this period.