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Elrathia Trilobite Facts and Information

Elrathia kingii is one of the most familiar Cambrian trilobites because it occurs in huge numbers in parts of the Wheeler Shale of Utah. In some layers, these fossils are so abundant that commercial quarries have long collected and sold them as classic examples of trilobite fossils from the American West. For many people, Elrathia kingii is the first real trilobite fossil they ever see, buy, or collect.

This trilobite lived during the Middle Cambrian, when Utah was covered by a shallow inland sea. The Wheeler Shale preserves a rich marine ecosystem that included trilobites, agnostids, brachiopods, sponges, worms, and other soft-bodied organisms. Elrathia kingii was especially successful in this environment and is often found alongside other Cambrian trilobites such as Asaphiscus wheeleri and tiny agnostid trilobites like Peronopsis.

Elrathia kingii has a broad thorax, short genal spines, and a relatively simple body form. Most specimens are about an inch long, though tiny juveniles and larger adults are also found. The simple outline makes Elrathia easy to recognize, especially when preserved as a dark fossil against gray shale. Many specimens are found without the free cheeks attached, which is common in trilobites because those parts separated during molting or after death.

Its body shape and mouthparts suggest that Elrathia was probably a particle feeder or scavenger living on the Cambrian seafloor. It likely moved across the bottom, feeding on organic particles and small bits of decaying material in the sediment. These trilobites are often associated with low-oxygen, or exaerobic, seafloor conditions. Those environments were stressful for many animals, but they also favored fossil preservation by slowing decay and limiting scavenging.

This combination of abundance, easy identification, and excellent preservation is why Elrathia kingii has become one of the most collected trilobites in North America. It is not the most ornate trilobite, but it is one of the best examples of Cambrian marine life and an important fossil for understanding the ancient Wheeler Shale ecosystem of Utah.

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Where to Find Elrathia Trilobite Fossils

Elrathia kingii trilobites are mainly found in the Cambrian Wheeler Shale of Utah and Nevada. The House Range near Delta, Utah, is especially famous for these fossils, and many collectors know Elrathia as the classic trilobite from U-Dig Fossils.

To find your own Elrathia kingii, the U-Dig Fossils quarry near Delta, Utah, is one of the most accessible collecting sites. Visitors split slabs of Wheeler Shale and look for dark trilobite fossils preserved on the bedding planes.

You can also read about my trilobite fossil collecting trip in the Wheeler Shale near Delta, Utah.

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Recommended Trilobite and Fossil Hunting Books:

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Elrathia kingii Fossil Examples

The following Elrathia kingii fossil examples come from the House Range of Utah and show several common preservation styles, including red specimens on colorful matrix, typical dark fossils on gray shale, and examples missing the free cheeks.

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References / Works Cited

Robison, R. A. (1964). Late Middle Cambrian faunas from western Utah. Journal of Paleontology, 38(3), 510-566.

Gaines, R. R., & Droser, M. L. (2010). The paleoredox setting of Burgess Shale-type deposits. Palaeogeography, Palaeoclimatology, Palaeoecology, 297(3-4), 649-661.

Utah Geological Survey. Cambrian fossils and trilobite collecting in Utah.

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