Introduction

The Cenozoic Era, sometimes referred to as the “Coenozoic” or “Age of Mammals,” marks a pivotal chapter in Earth’s history. Beginning about 66 million years ago, this era followed the dramatic extinction event that wiped out the dinosaurs. The Cenozoic is characterized by major evolutionary changes, especially the diversification and dominance of mammals, which have shaped the modern world.

Key Features of the Cenozoic Era

• Extinction of Dinosaurs: The Cenozoic Era began immediately after the mass extinction event at the end of the Cretaceous Period, which saw the disappearance of non-avian dinosaurs. This event opened ecological niches that mammals rapidly filled357.

• Adaptive Radiation of Mammals: With dinosaurs gone, mammals diversified and evolved into a wide variety of forms, occupying roles as herbivores, carnivores, and omnivores. This adaptive radiation led to the emergence of many modern mammalian groups, including primates, whales, elephants, and eventually, humans1567.

• Rise of Birds: Birds (the only surviving lineage of dinosaurs) also underwent adaptive radiation, but the era is especially noted for mammalian evolution15.

• Modern Flora and Fauna: The Cenozoic saw the rise of flowering plants (angiosperms), insects, and the development of modern ecosystems16.

• Continental Drift and Climate Change: During this era, continents moved to their current positions, and the Earth experienced significant climatic shifts, including ice ages26.

Periods of the Cenozoic Era

The Cenozoic is divided into three main periods:

• Paleogene (66–23 million years ago): Marked by the initial diversification of mammals and birds.

• Neogene (23–2.6 million years ago): Saw further evolution of mammals and the appearance of early hominids.

• Quaternary (2.6 million years ago–present): Characterized by repeated ice ages and the rise of modern humans2568.

Why Is the Cenozoic Called the “Age of Mammals”?

The extinction of dinosaurs removed the dominant terrestrial vertebrates, allowing mammals to rapidly diversify and occupy new ecological niches. This era witnessed the evolution of many mammalian lineages that are still present today, making mammals the dominant large animals on land1567.

The Correct Answer

Given the options:

1. Disappearance of reptiles and adaptive radiation in aves

2. Disappearance of dinosaurs and adaptive radiation in aves

3. Disappearance of dinosaurs and adaptive radiation in mammals

4. Appearance of mammals and aves

The correct answer is:

(3) Disappearance of dinosaurs and adaptive radiation in mammals

Conclusion

The Cenozoic Era is defined by the extinction of dinosaurs and the subsequent adaptive radiation of mammals. This era set the stage for the development of modern ecosystems and the rise of humans, earning its title as the “Age of Mammals.” Understanding the Cenozoic is essential for appreciating the evolutionary history that led to the world we know today.