Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Triassic
Extinction and Recovery
Origin of Mammals
Origin of the Dinosaurs
Climate and Plate Tectonics
Skull of Coelophysis
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Skull of Cynognathus
Skull of Buettneria
Bennettitalean 1
Bennettitalean 2
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Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Origin of the Dinosaurs
Dinosaurs are probably the most famous animals of the Triassic world, but none existed at the start of this time period. Synapsids dominated 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.


Overview | Extinction and Recovery | Origin of Mammals
Origin of the Dinosaurs | Climate and Plate Tectonics

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