In what geological time period are dinosaurs primarily known to have existed?

Dinosaurs are primarily known to have existed during the Mesozoic Era, which is often referred to as the "Age of Reptiles." This era spanned from approximately 252 to 66 million years ago and is divided into three periods: the Triassic, Jurassic, and Cretaceous.

During the Mesozoic, dinosaurs thrived, diversified, and became the dominant terrestrial vertebrates. The evolutionary history of dinosaurs is well-documented in the fossil record from this period, showing a range of species that occupied various ecological niches. The end of the Mesozoic marks the mass extinction event that led to the demise of the non-avian dinosaurs.

The other eras mentioned do not correspond to the time when dinosaurs were prevalent. The Paleozoic Era, which preceded the Mesozoic, includes earlier life forms such as fish, amphibians, and the first reptiles but not true dinosaurs. The Cenozoic Era follows the Mesozoic and is marked by the rise of mammals and birds, while the Precambrian covers the time before complex life forms emerged, not overlapping with the era of dinosaurs.