  Home | Exhibits | Life Through Time Exhibit | Silurian |
| Ordovician |
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Home | Exhibits | Life Through Time Exhibit | Silurian |
| Ordovician |
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The Silurian* lasted about 28 million years. There was a rapid recovery of biodiversity after the extinction event at the end of the Ordovician. A warm climate and high sea level gave rise to large reefs, while on land simple vascular plants emerged. Graptolites and trilobites were on the decline, while other major groups continued to flourish. Invertebrates remained dominant, vertebrate fossils are rare.
During the Silurian Earth's continent joined together, closing the Iapetus Ocean and forming two supercontinents: Laurasia in the north, and Gondwanaland to the south. The plate movements resulted in movement of the Souith Pole over South America and southern African Gondwana. There were strong world-wide sea-level changes oceanic turnovers, associated with moderate extinctions.
* The Silurian was named by Murchison in 1839 for the Silures, a tribe of the Welch borderland.
Silurian Animal (Metazoan) Fossils |
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Trilobites (ToL: Trilobites<Arthropoda<Ecdysozoa<Bilateria<Metazoa<Eukaryota) |
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Trilobites were on the decline in the Silurian, but still abundant locally. Species included in this display are: Cyphaspis christyi, Diacalymene clavicula, and a rolled-up specimen. |
Euryptides (ToL: Euryptida<Chelicerata<Arthropoda<Ecdysozoa<Bilateria<Metazoa<Eukaryota) |
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Eurypterides (Sea Scorpions) were predatory arthropods during most of the Paleozoic (Ordovician - Permian). |
Echinoderms (ToL: Echinodermata<Deuterostomia<Bilateria<Metazoa<Eukaryota) |
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| Three extant groups of echinoderms are represented on a single specimen: starfish, brittlestars, and sea-lilies. (Can you find them all?) | |
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Crinoids (Crinoidea). A number of sea-lilies (stalked crinoids) are displayed: Eucalyptocrinites crassus (plate-covered theca & stem), and an unidentified species showing the flower-like crown on a stem. Note the second stem showing the less often preserved arms. There is also a crinoid stem embedded in rock. |
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Cystoids (Blastoidea?). Two cystoids (primitive blastoids?) generally stemmed organisms with globular or pear-shaped theca with round or slit piercings, are represented: Caryocrinus sp. and Holocystites scutellatus. |
Mollusks (ToL: Mollusca<Lophotrochozoa<Bilateria<Metazoa<Eukaryota) |
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Gastropods (Gastropoda): Two gastropod snails are represented, a flat Tropidodiscus sp. embedded in rock, and a snail (note the brachiopod and crinoid fragments also present). |
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Cephalopods (Cephalopoda): A nautilous, cone-shaped cephalopod is represented. |
Brachiopods (ToL: Brachiopoda<Lophotrochozoa<Bilateria<Metazoa<Eukaryota) |
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Brachiopods: Specimens of two species of brachiopod are displayed: Eosirifer sp. and Pentamerus sp. |
Corals (ToL: Cnidera<Metazoa<Eukaryota) |
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Cnidarians (corals): Specimens from two extinct coral groups, the large, generally solitary Horn coral (subclass Rugosa), and the colonial tabulate pipe coral Syringopora (subclass Tabulata) are shown. There is also a colonial coral. |
Sponges (ToL: Porifera<Metazoa<Eukaryota) |
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Sponges: Three different species of sponge are displayed. First is the cup-shaped Astraeospongia meniscus. Note the star-shaped spicules apparent in this specimen. There are two, small specimens of globular sponges: Caryospongia and Astrospongia. |
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Stromatoporidea: These important Silurian and Devonian period reef-building organisms are thought to be sponges, though they were previously classified as corals. The fossils are encrusting, cylindrical, or massive. The museum has a fragment, and an encrusting specimen. |
Silurian Plant Fossils |
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Green Algae (ToL: Green Plants<Eukaryota) |
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| Recepticulites: Until recently classified as sponges, recepticulites are now thought to be fossils of algae of the division Chlorophyta. They lived from the Ordovician to the Permian. Whole specimens are globular to platter shaped. On display are a near complete globular example, and two fragments showing pore structure and the rectangular plate structures characteristic of these organisms | |
The engravings are from Dana, James D. (1870) Manual of
Geology, Le Conte, Joseph (1898) A Compend of Geology, Louis Pirson and Charles Schuchert, A Text-Book of Geology.
(1920), or H. Alleyne Nicholson (1876) The Ancient Life-History of the Earth.
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Last modified 29 January 2007 | ©1998, HSU NHM
