Final answer:
Dinosaurs indeed outcompeted other reptiles during the Late Triassic period after a mass extinction event, allowing them to become the dominant terrestrial vertebrates and diversify into various niches, leading to their dominance throughout the Mesozoic era.
Step-by-step explanation:
It is true that dinosaurs outcompeted other reptiles during the Late Triassic period. Following the mass extinction at the end of the Triassic around 200 million years ago, dinosaurs became the dominant terrestrial vertebrates. During this time, the first dinosaurs branched off from other reptiles and began to diversify into various niches.
Dinosaurs continued to dominate through the Mesozoic era, also known as the 'Age of Reptiles', which spanned another two periods after the Triassic: the Jurassic and the Cretaceous periods. The Mesozoic era ended with the Cretaceous-Tertiary extinction event, which led to the demise of most large-bodied animals from that era, including dinosaurs. Birds, today, are considered the only living descendants of theropod dinosaurs.
The post-Triassic mass extinction event paved the way for the rise of dinosaurs, as they filled ecological niches left vacant by other groups. This era is also when mammals began to evolve, although they remained small compared to the dominant dinosaurs. Therefore, variations of dinosaurs flourished during the Jurassic, which is often referred to as the golden age of dinosaurs.