|Origin of the Dinosaurs
are probably the most famous animals of the Triassic world, but none existed at the start of this time period.
the land until the Middle Triassic, when many synapsids began to disappear.
Whether this change was gradual or a sudden extinction is still debated
among paleontologists, but by the Late Triassic the landscape was
very different. Instead of synapsids, an entirely different group
had risen to dominance, the archosaurs. Archosaurs
included dinosaurs, pterosaurs, and crocodyliforms, as well as a bizarre
array of other animals (such as phytosaurs and rhynchosaurs).
At the close of the Triassic, archosaurs were common in the air, on
land, and in the seas.
The earliest dinosaurs are known from Argentina and include predatory
theropods (Herrerasaurus, Eoraptor) and herbivorous
ornithischians (Pisanosaurus). By the end
of the Triassic, dinosaurs were widespread and dominated most terrestrial
ecosystems. The most abundant were small theropods
such as Coelophysis (from North America), and large, herbivorous
prosauropods such as Plateosaurus (from Europe).
Rare evidence also exists of other groups, including the first sauropods
and armored dinosaurs. During the following Jurassic Period, dinosaurs
and other archosaurs would become even more diverse and spectacular,
evolving into gigantic sauropods, large theropods,
and birds. Their dominance would continue until the
end of the Mesozoic.