"Dawn of the Dinosaur Age" presents the first act in the drama that would become the Mesozoic Era, the Age of Reptiles. The rise of the first dinosaurs is the story of opportunity and evolutionary innovation. The first dinosaurs, after living in the shadows of larger, more dominant reptilian kin, took advantage of major mass extinctions at the end of the Triassic Period to take over niches once occupied by their predecessors. In the course of doing so, dinosaurs quickly radiated to widespread geographic ranges and began an evolutionary course that led to the development of two major groups of dinosaurs, the Saurischia and Ornithischia.The Late Triassic and Early Jurassic Periods were a time of experimentation in dinosaur evolution as the earliest herbivorous and predaceous dinosaurs adapted increasingly specialized body forms and lifestyles. "Dawn of the Dinosaur Age" explores the roots of the dinosaur family tree and the lifestyle and radiation of the first carnivorous and herbivorous dinosaurs.