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.
St Brides Major (community) St Brides Major, the Dunraven estate and Clemenstone Meadow SSSI. Much of the coastline of the community is designated as the Southerndown Coast SSSI, both for its geology and botanic value. The stretch of shore, cliff, cliff-top, and several short, steep valleys, reveal the local geological strata. Carboniferous Limestone from upwards of 300 million years ago lies at the present sea level. By the Triassic period, 200 million years ago, these rocks were already tilted and eroded. A new deposition phase created more sedimentary rocks, including a red Triassic conglomerate, and a creamy white Jurassic limestone known as Sutton Stone,