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agnostid trilobite fossils from Utah.

Agnostid Trilobite Facts and Information

Agnostid trilobite fossils are very peculiar in that they have no eyes, the head (cephalon) and tail (pygidium) look very similar and the thorax only has two segments. They look like a miniature peanut!

They are quite tiny! A small one can be under a millimeter, while a large one is about 10 mm. When found, they often look like flecks of pepper on the rock. A death plate that contains a dozen can be as small as a few inches in size!

The agnostida order appears in the Cambrian and dies out in the Late Ordovician.

Because of their peculiar morphology, the ecology of this trilobite has been debated. Based on the morphology and associated fossils, most people think they were benthic, living on the bottom of the sea. They are often found in groups, and often found underneath and inside other fossils, suggesting they indeed lived on the sea floor. Also the lack of eyes is consistant with living on the ocean floor with very little light.

The key characteristic in identifying a cephalon from a pygidium is the pygidial axis (middle of the pygidium) runs closer to the end of the pygidium than the glabella on the cephalon. If this sounds confusing, which it does, the diagram below will straighten it out.

As far as identifying species and genera, it appears to be a delicate science taht requires the use of many journal articles. Idntification to a genus and species level will not be attempted here. While doing research, it appears many people blindly assign a species name or genera without knowing for sure.

There are numerous genera and dozens of species of agnostid trilobites. They appear to have a global distribution in Cambrian exposures, North America to Africa and Australia.

The agnostid trilobite fossils featured here, are either Peronopsis, Ptychagnostidae, and peraps Onymagnostus, come from the Cambrian Wheeler shale and Marjum formations from the House Range in Utah.

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Where to find Agnostid Trilobite Fossils

Egnostid trilobites are found globally throught Paleozoic formations that contain trilobites. They are most abundant in Cambrian formations. Easy places to find them are the Wheeler Shale in Utah and Nevada. They look like little pepper flakes on the rocks.

To try and find your own Agnostid trilobites, I would suggest going to the U-Dig quarry near Delta, Utah.

Click here to read about my trilobite fossil collecing trip in the Wheeler Shale near Delta, Utah

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Recommended Trilobite and Fossil Hunting Books:

Trilobites from Fossil Era
Trilobite fossils are some of the most beautiful and collectible fossils in the world! They make beautiful display and conversation pieces. They can make very affordable for gifts to fossil and paleontology enthusiasts. Fossil Era has a huge selection of top quality trilobites. It's fun just to browse through the inventory and look at all the different types!

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Agnostid Trilobite Fossil Examples

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