Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Triassic
Contents
Overview
Extinction and Recovery
Origin of Mammals
Origin of the Dinosaurs
Climate and Plate Tectonics
Evidence
Skull of Coelophysis
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sample
Dicynodont
Dicynodont
Cynodont
Skull of Cynognathus
Skull of Buettneria
Phytosaur
Nothosaur
Bennettitalean 1
Bennettitalean 2
Cycadophyte
Trilophosaurus
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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Origin of Mammals
Although the Triassic Period is often remembered as the time when dinosaurs and other archosaurs rose to dominance, mammals and their ancestors also played an important role. In fact, these synapsids (once called “mammal-like reptiles”) were very abundant in the early Triassic world. They came in a wide variety of sizes and shapes, from large, cow-like dicynodonts (such as Lystrosaurus), to fanged, carnivorous gorgonopsians, to tiny insectivorous tritylodonts. A Triassic landscape in South Africa would have been filled with great numbers of these early synapsids. By the Middle Triassic (about the same time as the first dinosaurs) one of these synapsid groups had evolved into the very first mammals. Although many different types of mammals evolved later in the Mesozoic, for the most part they remained small, probably because of the dinosaurs' success. However, later in the Mesozoic some mammals achieved the size of a 30 lb. (13 kg) dog despite the dominant success of the dinosaurs. Many types of mammals appeared in the Mesozoic, and evidence from Early Cretaceous outcrops (130 million-years ago) in China shows that at least one carnivorous mammal, Repenomamus robustus, feasted on small dinosaurs.



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



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