The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives. During Mesozoic and Early Tertiary times, the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were supplanted during the Early Jurassic by various aquatic and marine forms. The Late Jurassic, Cretaceous, and Tertiary saw a wide diversity of terrestrial and semi-aquatic lineages. "Modern" crocodilians do not appear until the Late Cretaceous.