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
learn more
Skull of Cynognathus
Skull of Buettneria
Bennettitalean 1
Bennettitalean 2
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
Privacy Statement Copyright
Glossary Credits Email Us

Extinction and Recovery
The first third of the Triassic was a recovery period from the end-Permian extinction. This greatest extinction in Earth’s history, eliminating approximately 70% of the species of land vertebrates and 90% of marine animal species, sharply reduced the number of different ways in which plants and animals made a living. During the Triassic life re-evolved many strategies for living, and added new ones not seen during the Paleozoic. Newly evolved scleractinian corals formed small reefs, beginning the recovery of reef ecosystems. Mollusks such as ammonoids (relatives of the modern chambered nautilus) were severely reduced in diversity by the extinction but evolved rapidly afterward to become more diverse than ever before and to dominate the open-ocean marine invertebrate world.

Recovery from extinction was far from uniform among the surviving groups. Echinoderms had been nearly wiped out, and brachiopods had been severely reduced in diversity; but while brachiopods never fully recovered, echinoderms flourished in the Triassic. Two new types of echinoderms, echinoids (e.g., sea urchins) and asteroids (e.g., starfish), appeared for the first time. All major groups of land plants survived the end-Permian extinction, but families, genera, and species of plants in the Triassic were generally distinct from their Permian relatives. Globally, many Early Triassic floras were dominated by club mosses (Pleuromeia) or mosses. The glossopterids (a type of seed fern), which had been dominant plants in the Permian of the Southern Hemisphere, never recovered their former abundance or diversity; Triassic floras of this area were characterized by a different type of seed fern called Dicroidium. In the tropical regions of Euramerica the Early Triassic was a time of low-diversity vegetation. Conifers, which had been dominants in the Late Permian, were rare or absent for millions of years in the Early Triassic until new families of conifers diversified in the Middle Triassic. Bennettitaleans and cycads also diversified in the Triassic and became important components of the terrestrial vegetation.

New types of animals and plants continued to evolve throughout the Triassic. The first mammals and dinosaurs originated almost simultaneously, in the late Middle or early Late Triassic. The oldest known fossil of an amniote egg is from the Early Triassic. In the seas, ichthyosaurs (dolphin-shaped reptiles), nothosaurs, and placodonts (mollusk-eating reptiles) appeared and thrived. Some ichthyosaurs reached lengths of 23 meters (75 feet). Turtles, crocodyliforms, and pterosaurs all made their debuts, along with frogs and sphenodontians. In fact, by the end of the Triassic, many of the animal groups we see today had made their first appearances on Earth.


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

Department of Paleobiology Home | National Museum of Natural History Home
Smithsonian Institution Home