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Triarthrus Trilobite Facts, Information, and Fossil Examples

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Beautiful Triarthrus eatoni trilobite fossil from New York

Fast Facts about Triarthrus Trilobites

Name: Triarthrus (pronunciation: "TRI arth rus") - Common Species in New York: Triarthrus eatoni

Taxonomy: Phylum: Arthropoda - Class: Trilobita - Order: Ptychopariida - Family: Olenidae - Genus: Triarthrus

There are many species of Triarthrus. More common species include: beckii, canadensis, and eatoni.

Age: Ordovician

Distribution: North America, Northern Europe, and China
In North America, they are most commonly found in Kentucky, New York, Quebec, and Ontario.

Body Size:
Triarthrus are somewhat small trilobites and grow to around 5 cm, or 2" in length.

Physical Appearance:
Narrow with a long thorax, have a small pygidium, and a plain looking cephalon. The cephalon has a series of glabellar furrows (parallel ridges running across the glabella). The eyes are slender, and often difficult to see in specimens.

Fun Fact
Triarthrus trilobites have been made world famous because of specimens being found with soft tissue preservation.
These specimens come from the Beachers Trilobite Bed in New York. The fossils show piratized gills, legs, antennae, mouth parts, and even Triarthrus trilobite eggs.

Pyratized Triarthrus Trilobite showing appendages - By Didier Descouens (Own Work)
By Didier Descouens (Own work) 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.

Triarthrus Trilobites - The Details

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.

closeup of fossil trilobite eyes showing the lenses
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.
Fossil Info: Triarthrus eatoni - Central New York - Ordivician - Utica Shale

Recommended Books and Fossils

Trilobties for Sale:

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

Recommended Books (also in kindle format):

The Trilobite Book: A Visual Journey
by Dr. Riccardo Levi-Setti, 2014

This is an updated (2014) hardcover (kindle available) of his famous 1994 book. It now has color images instead of black and white ones. The images are of prefectly prepared trilobites from all over the world. this book is geared toward the beginner and does not get overly technical. However, it's wonderful just to see the pictures, and a must for any trilobite enthusiast.

Trilobite: Eyewitness to Evolution
by Dr. Richard Fortey, 2001

Dr. Fortey is a famous natural history writer from the British Museum of Natural History. He brings trilbites to life in this well crafted and enjoyable narrative. He merges science and history together to show us the big picture about trilobites. It's a nice read for anyone interested in Trilobits.

Trilobites: Common Trilobites of North America (A NatureGuide Book)
by Jasper Burns, 2000

I love Jasper Burns. His Fossil Collecting in the Mid-Atlantic book is still one of my favorite fossil books. His drawings are spectacular and the books are well laid out. This book serves as a field guide and identification guide to North American trilobites. If you fossil hunt for trilobites in North America, you should have this book!

Triarthrus Fossil Examples

Triarthrus eatoni Trilobites

The Ordovician rocks of New York are one of the easiest places to find Triarthrus trilobites.

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.

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

Fossil trilobite: Triarthrus eatoni from New York

That little bluish feather looking thing against the cephalon might be a graptolite.

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

Triarthus molt plate - These are numerous molted Cephalons that accumulated

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

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