Mesozoic that would move into their current positions during the next era. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs appeared in the Late Triassic and became the dominant terrestrial vertebrates early in the Jurassic, occupying this position for about 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic, having evolved from a branch of theropod dinosaurs. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic.
Eldon George as a sparrow or robin. In 1986, a scientific team that included Paul Olsen, discovered hundreds of thousands of fossils at Wasson Bluff, one of the biggest troves ever found. Fossil discoveries on the Fundy shoreline are especially significant because they date from 200 million years ago, the boundary between the Triassic and Jurassic geological periods, when about half of the Earth's living creatures suddenly became extinct giving rise to dinosaurs and the mammals that eventually succeeded them. Many of the fossils that date from that time remain hidden, buried under North American forests, farmland or cities. But, the Fundy