Here's a breakdown:
* Before the dinosaurs (Paleozoic Era, specifically the Permian Period): Synapsids were the most successful group of land animals. They were a diverse group, ranging from small, insect-eating creatures to large, carnivorous predators. One of the most famous synapsids is Dimetrodon, known for its distinctive sail-like fin on its back.
* The Rise of Dinosaurs (Mesozoic Era, specifically the Triassic Period): While synapsids were still around, the dinosaurs began to diversify and eventually became the dominant land animals. This shift likely happened due to a combination of factors, including climate change and the Permian-Triassic extinction event (the largest known mass extinction in Earth's history).
* Synapsid Legacy: Though they were overshadowed by dinosaurs, synapsids left an important legacy: mammals evolved from them! So, you can think of the mammals we know today as the descendants of the pre-dinosaur reptiles.
In short, the dominant life forms before the dinosaurs were a group of reptiles called synapsids, which included the ancestors of mammals.
