Celebrating the Richness of Paleontology through Fossil Hunting

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The Trilobite Gallery

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Triarthrus Trilobite Gallery

Beautiful Triarthrus eatoni trilobite fossil from New York

Triarthrus Trilobite Facts and Information:

Triarthrus trilobites, of the Ptychopariida Order, are known from the Upper Ordovician rock in North America and Northern Europe.

These trilobites are narrow with a long thorax, have a small pygidium, and a plain looking cephalon. One notable feature on the cephalon is the presence of a series of glabellar furrows (It has a wide glabella with notable parallel ridges running across it). The eyes are slender, and often difficult to see in specimens, unless they are well preserved.

Based on the strata they are found in, they appear to have lived on the sea floor near the exareobic zone, a zone that is below the oxygen level required by most organisms. Elrathia of the Cambrian also lived in this type of environment.

Triarthrus trilobites would have been an often overlooked, indistinct trilobite if it wasn't for its preference toward exareobic environments. These environments of little oxygen tend to favor fossilization. In one of these places in the Frankfort Formation, called Beecher's Trilobite Bed, Pyrite has delicately preserved Triarthus to the point of soft tissue preservation. In the Beecher's Trilobite Bed, which is only a few centimeters thick, come some of the finest preserved fossil trilobites in the world. An image of some of these Pyritized Triarthrus trilobites with soft tissue preservation is shown to the right.

Pyratized Triarthrus Trilobite showing appendages - By Didier Descouens (Own work)
By Didier Descouens (Own work) [GFDL or CC-BY-SA-3.0-2.5-2.0-1.0], via Wikimedia Commons
This image shows pyritized Triarthrus trilobites with their soft appendages preserved. These amazing fossils come from Beechers' Trilobite Bed in NY.

Phylum: Arthropoda
Class: Trilobita
Order: Ptychopariida
Suborder: Olenina
Family: Olenidae
Genus: Triarthrus
Species: eatoni, becki, rougensis
Locality Information:
Triarthrus Trilobites are found in Upper Ordocivian units in North America and Scandanavia.

The Triarthrus trilobites on this page are T. eastoni from an outcropping in central New York of the Indian Castle Member of the Utica Shale.

Click Here to View a Triarthus Trilobite and Eurypterid Fossil Collecting Trip Report
Triarthrus Trilobite Fossil Hunt Fossil Collecting for Triarthrus Trilobites

Triarthrus eatoni Fossil Examples

Triarthrus eatoni Trilobite Fossil from New York

This Triarthrus trilobite is a little chipped up, but it has a nicely preserved cephalon. Triarthrus have eyes, however, due to poor preservation, they are often not seen.

Location:Central New York
Age: Ordovician
Formation: Utica Shale

Fossil trilobite: Triarthrus eatoni from New York

Here is another Triarthrus eatoni trilobite fossil. It is not as well preserved, but has no chips in it.

Location:Central New York
Age: Ordovician
Formation: Utica Shale

Triarthrus Trilobite Fossil from New York

This is a Triarthrus trilobite fossil with part of the cephalon sheered off. Unfortunately, many compete ones seem to be found like this.

Thatlittle bluish feather looking thing against the cephalon is a graptolite.

Location:Central New York
Age: Ordovician
Formation: Utica Shale

Triarthus molt plate - These are numerous molted Cephalons that accumulated

Cephalon hash plates are occasionally found in the Utica shale. These are probably from molts. Since the Triarthrus cephalons all have the same shape, they probably all accumulated together in the currents, then fossilized.

Location:Central New York
Age: Ordovician
Formation: Utica Shale