Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Ordovician
Contents
Eon Overview
Reef Ecosystems and the Paleozoic Fauna
New Animals as Biostratigraphic Tools
Ordovician Climate and Plate Tectonics
Evidence
Ordovician trilobite
learn more
sample
Starfish
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
Privacy Statement Copyright
Glossary Credits Email Us


Reef Ecosystems and the Paleozoic Fauna
Life in the Ordovician was quite different from that in the Cambrian. Although many animal groups survived from the Cambrian, some forms disappeared and other forms appeared for the first time. These changes marked the Ordovician as the first example of the Paleozoic Fauna. During this time, bryozoans, mollusks, echinoderms (particularly the fan-like crinoids), brachiopods, and trilobites diversified; these groups would dominate marine faunas throughout the Paleozoic. Many of the unusual animal forms seen in the Burgess Shale had gone extinct, but graptolites, conodonts, nautiloids, and jawless fishes had their first known appearances.

These new animals radiated alongside the rugose and tabulate corals that replaced the Cambrian archaeocyaths. In fact, entirely new types of ecosystems evolved in the Ordovician, associated with the development of many types of carbonate (limestone) marine shelves (or platforms). These warm, shallow-water formations were flooded with sunlight, allowing the establishment of stable reef ecosystems. These included the first coral/algal reefs, shallow-water assemblages of mollusks, brachiopods, echinoderms and trilobites, and more-diverse underwater slope and deeper-water faunas. Many of these faunas would become even more important in later Paleozoic periods.

Small but significant, lichens and bryophyte plants also appeared in the Ordovician and began the first of many colonizations of dry land. However, the end of the Ordovician saw the second-largest mass extinction of the Paleozoic, resulting in the loss of many different animal species. One-third of all brachiopod and bryozoan families disappeared, as well as many types of trilobites and reef-building animals. Even some of the newly evolved graptolites and conodonts went extinct.




Overview | Reef Ecosystems and the Paleozoic Fauna | New Animals as Biostratigraphic Tools
Ordovician Climate and Plate Tectonics



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