Polymerida

trilobite order

Also known as: polymeroid

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July 1, 2026

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The Polymerida were an order of extinct marine arthropods known as trilobites. Trilobites first appeared at the beginning of the Cambrian Period, approximately 521 million years ago, and were characterized by a three-lobed, three-segmented body. The Polymerida order comprised about 95 percent of all trilobite species, typically possessing more than five thoracic segments.12

While Polymerida are useful for regional correlation of Cambrian rocks, their limited intercontinental distribution makes them less valuable for global stratigraphic correlations compared to trilobites from the order Agnostida. Polymerida lived on the seafloor and were mostly endemic to the shelves of individual Cambrian continents.2

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Cambrian Period
Correlation of Cambrian strata
…on members of the order Polymerida. Such trilobites usually have more than five segments in the thorax, and the order includes about 95 percent of all trilobite species. Most polymeroids, however, lived on the seafloor, and genera and species were mostly endemic to the shelves of individual Cambrian continents. Therefore,…
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…on members of the order Polymerida. Such trilobites usually have more than five segments in the thorax, and the order includes about 95 percent of all trilobite species. Most polymeroids, however, lived on the seafloor, and genera and species were mostly endemic to the shelves of individual Cambrian continents. Therefore,…
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