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Eldredeaops (Phacops) rana Trilobite Fossil from New York

Eldredgeops (Phacops) Very Special Trilobite Eyes

A conspicuous feature is their eyes. For a trilobite, the suborder of Phacopina, including Eldredgeops and Phacops, have very sophisticated eyes called schizochroal eyes. These are large, round, and bulbous eyes. They contain many calcite lenses separated by tissue called sclera (this tissue makes up the whites of your eyes). These eyes had overlapping visual fields (depth perception) and possible color perception (Stockton and Cowen, 1976). They could also swivel, creating a 360 degree field of view. Stockton and Cowen say these special eyes were fundamentally different than any compound eye in existence today. Because the eyes slightly resemble the eyes of a frog, the most common species name is "rana" which is latin for "frog".

Besides the eyes, the glabella (nose looking area that actually contains part of the digestive system) is very large, and contains many small bumps. The rest of Eldredgeops is somewhat plain. The cephalon (head) and pygydium (tail) is rounded. The thorax is plain looking. Like other trilobites, as Eldredgeops grew, it molted and gained additional thorax segments.

Very similar looking genera in this suborder include Reedops, Kainops, Phaciphacops, Phacops from Morocco, and the large Drotops from Morocco. Each genus has small differences in the cephalon and has different numbers of lenses in the eyes.

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Phacops or Eldredgeops? - Why the Trilobite name change?

These North American Trilobites are popularly called Phacops, but should be corectly called Eldredgeops. Why the name duality? These trilobites were originally called Phacops, and that's what fossil hunters have collectively known them as for decades. However, in 1990, the genus was renamed Eldredgeops. Here's the short version as to why:

During the Devonian, in the Eldredgeops/Phacops heyday, Africa / South Europe and North America / North Europe were separated by a narrow sea called the Rheic Ocean. Because it was so narrow, many of the trilobites on either side looked very similar. Originally, the "Phacops" looking trilobites on either side of the ocean were both assigned to the genus Phacops.

Then in 1990, Struve did an in-depth study of the morphology of the Phacops genera. He concluded there were enough slight physical differences between the "Phacops" on the North American side and the Phacops on the African side to break them into separate genera.

He renamed the Phacops lineage on the Eastern side of the Rheic Ocean (North America and Northern Europe) to the genus Eldredgeops (Based on an Ohio type specimen). Since phacops was originally described based on a specimen from Germany, he kept the lineage on the Western side of the Rheic Ocean (North Africa/Middle East/South Europe) as Phacops.

So now the North American "Phacops" trilobites are officially called Eldredgeops. This new name tends to be unpopular with fossil hunters because the old name "Phacops" is engrained in the fossil culture and it's just so much easier to say!

Will this classification ever change? If you have been a fossil hunter for a while, you know it very well could. Revisions will occur, new names pop up and old names may become valid again. Who knows!

If you don't understand what I just said in the above paragraphs, all you need to know is this:
If you find a "Phacops" trilobite in North America: West Virginia, Virginia, Pennsylvania, New York, or Ohio, it's most likely an Eldregeops.

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Phacopid Trilobites: Predatory Behavior

While some orders of trilobites were particle feaders, suspension feeders, and others were filter feeders (See Cryptolythus), it's thought that the Phacopidae family (including Eldredgeops) were benthic (sea floor) predators.

There are many reasons for this line of thought. Some of them include the following:

The Glabella
Phacopid trilobites had enlarged glabellas. The glabella held most of the digestive system. A large glabella indicates these trilobites would have consumed large chunks of prey, and not just small particles.

Size
Owens, 1999, correlates larger trilobites to a predatory lifestyle, while smaller ones were mainly filter feeders and particle feeders. Since Eldredgeops were some of the larger trilobites of the time. These larger arthropods could have been the predators on the sea floor.

The Eyes
Since Eldredgeops' schizochroal eyes were a very remarkable visual system , which had nearly 360 degree field of view and depth perception, Stockton and Cowen, 1976, suggests Eldredgeops (Phacops) was an active benthonic animal. There is no need for such sophisticated eyes in a scavenger.

The hypostome (Mouth Parts)
Finally, the mouth part of Eldredgeops, the hypostome, was branched and had a "considerable freedom of movement" (Miller 1976), indicating it could manipulate large and possibly struggling prey.

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Eldredgeops (Phacops) Trilobite Enrollment:

If an Eldredgeops was threatened, it could completely enroll forming a very strong ball. While some types of trilobites could only partially enroll, Eldredgeops, could fully enroll for protection. The cephalon would make a tight seal with the pygydium. This would create a formidable defense from other larger Devonian predators.

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Castro, Jose L. (1996). Sharks of North American Waters. College Station: Texas AandM University Press.

Fortey, R.A. & Owens, R.M. (1999) Feeding habits in trilobites. Palaeontology 42(3),429-465. DOI 10.1111/1475-4983.00080

Miller, J. (1976) The sensory fields and life mode of Phacops rana (Green, 1832). Transactions of the Royal Society of Edinburgh, 69, 337-67.

Stockton, W. L. and Cowen, R. (1976) Stereoscopic vision in one eye: paleophysiology of the schizochroal eye of trilobites. Paleobiology, 2, 304-315.

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Where to find Eldredgeops (Phacops) Trilobite Fossils

Eldredgeops (Phacops) is common in many middle Devonian formations in the Eastern United States. Some of the notable formations where Eldredgeops (Phacops) trilobites are found include:

Needmore formation in West Virginia
Mahantango formation in Pennsylvania, West Virginia, and Virginia
Hamilton Group of Western New York
Silica shale of Ohio
Haragan formation in Oklahoma
Little Cedar Formation in Iowa

If you want to hunt for your own Eldredgeops trilobite, click on one of the above formations for specific fossil collecting information, including fossil hunting locations and directions.

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Recommended Trilobite and Fossil Hunting Books:

Trilobites for Sale:

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Eldredgeops (Phacops) Fossil Examples

E. rana crassituberculata

Ohio has some of North Americas largest Eldredgeops trilobites. They are E. rana crassituberculata.

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E. rana crassituberculata

Ohio has some of North Americas largest Eldredgeops trilobites. They are E. rana crassituberculata.