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Name: Cedaria minor

Location: Utah, USA, Weeks Formation

Age: 444-461 million years ago, Cambrian Period

No one has ever seen a living Cedaria, or any other trilobite. Even though they were one of the most diverse groups of animals ever known, the last living trilobite died 250 million years before any human walked on Earth.

Trilobites were ocean-dwelling animals with many legs and hard, outer plates. So far, researchers have recognized and named over 20,000 species of trilobite. That’s an amazing diversity. In comparison, all of the different kinds of birds alive today, from ostriches to sparrows to penguins, add up to only half as many species. There are more than three times as many species of trilobites as there are species of mammals.

Trilobites had more than large numbers. They also came in a diversity of forms and sizes.

Cedaria was small, and would fit on a dime. In contrast, some of the other trilobite species grew forty times larger, and reached 72 centimeters, about the size of a freight-truck tire. Others grew to be only a tenth of a centimeter, about the width of a grain of rice.

The abundance and diversity of trilobites helped them make it through two mass extinctions, times when many other groups went extinct.

However, by the time a third mass extinction hit 250 million years ago, trilobites had lost the diversity and abundance that had helped them thrive. At the end, only a handful of trilobite species were left to go extinct.

Specimen Number: NPL 15006

Sources:

Gon, Sam III. “A Guide to the Orders of Trilobites,” accessed 9 October 2012. http://www.trilobites.info.

Hughes, Nigel C. “The evolution of trilobite body patterning.” Annual Review of Earth and Planetary Sciences 35(2007):401-434.

IUCN. “Summary of number of animal species in each Red List Category in each taxonomic class.” In: IUCN Red List of Threatened Species. Version 2012.1. Accessed 9 October 2012. http://www.iucnredlist.org/documents/summarystatistics/2012_1_RL_Stats_Table_3a.pdf

Where are similar fossils found?