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from | Encarta |  |
Fossilized Trilobites |
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| Although trilobites became extinct about 250 million years ago, they left detailed casts in the rocks where they died. This silica shale formation shows several trilobites. Because these primitive arthropods were typical organisms of the Paleozoic era, a paleontologist may use them to determine the relative age of the rock strata. | ||||||
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| James L. Amos/Photo Researchers, Inc. | ||||||
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| Appears in these articles: | ||||||
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| Fossil; Index Fossil; Invertebrate; Evolution; Paleontology; Extinction (biology); Trilobite; Arthropod; Cell (biology) | ||||||
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