During which geological era did dinosaurs primarily exist?

Dinosaurs primarily existed during the Mesozoic Era, which lasted roughly from 252 to 66 million years ago. This era is often called the "Age of Dinosaurs" because it is when they first appeared and became dominant land animals. The Mesozoic is subdivided into three periods: the Triassic, Jurassic, and Cretaceous. Each of these periods saw significant developments in dinosaur evolution and diversity, as well as the emergence of many other important life forms.

The other geological eras mentioned are characterized by different dominant life forms; for example, the Paleozoic Era is known for the flourishing of marine life and the early development of amphibians, while the Cenozoic Era follows the extinction of dinosaurs and is known for the rise of mammals and flowering plants. The Precambrian Era, on the other hand, precedes all these eras and covers the vast majority of Earth's history before the appearance of most multicellular life forms. Thus, the Mesozoic Era is the correct answer as it specifically correlates with the time when dinosaurs thrived on Earth.