Distinguishing Devonian Phacopid Genera from Oklahoma

“Ditto” said Tweedledum.
“Ditto, ditto!” cried Tweedledee.—from Through the Looking Glass And What Alice Found There by Lewis Carroll

Kainops, Devonian Period, oklahoma
Kainops, Early Devonian Epoch, Oklahoma. Note the relatively “tall” eyes, in this case with seven lenses in most files. All images taken with Canon 7DII/100mm f/2.8L IS Macro (+12mm Extension Tube II). High-speed synchronized macro ring-flash. Specimen collected and prepared by Bob Carroll. Specimen 1.8 cm across genals.

As noted in previous posts, this blog is an attempt to get back into the world of trilobite collecting after a long absence. Part of that process is digging through the collection and re-familiarizing myself with some of the finer points of the hobby.

One of the trickier areas of identification among commercially available specimens involves phacopids from the Devonian of Oklahoma. Four genera of these phacopids are easy to obtain commercially, but, I would add, not to collect or to tell apart! In fact, in going over many of my specimens I have found that some have been misidentified by the dealers I bought them from. Fool me once . . . .

As a result of that finding, I want to have a quick and dirty guide available in my head when at the shows and in the field, at least to the generic level. In this post I have chosen to discuss the eyes and surrounding areas. Distinguishing Kainops species (and morphs) adds a layer of difficulty that will not be addressed here. Interested readers can pursue greater detail in Hanson (2009) as a starting point.

The trilobite enthusiast should certainly be able to distinguish Paciphacops and Kainops, the two more common genera of Devonian phacopids from Oklahoma. As you can tell from the images above and below, the eyes allow fairly easy identification. But the picture gets a little murkier when we consider the other genera . . . .

Paciphacops, Devonian Period, Oklahoma
Paciphacops, Early Devonian Epoch, Oklahoma. Note the relatively “short” eyes, in this case with three lenses in most files. Specimen collected and prepared by Bob Carroll. Specimen 2.5 cm across genals.

Unfortunately, Kainops is not the only genus with “tall” eyes, and Paciphacops is not the only genus with “short” eyes.

Lochkovella is a much rarer trilobite that resembles Kainops in terms of eye structure. Fortunately, the eye in Lochkovella rides lower on the cephalon than in its more common cousin. Further, Lochkovella has a different surface texture on the cephalon. The texture in this genus may be described as granular and covers most of the cephalon. The “granules” are more or less the same size everywhere. In Kainops, however, the texture can be described as tubercular. Inspection of the specimen at the of the post shows that the tubercles vary in size across the cephalon, more like Paciphacops than Lochkovella.

Reedops deckeri, Devonian Period, Oklahoma
Lochkovella deckeri (formerly Reedops deckeri), Haragan Formation, Early Devonian Epoch, Coal County, Oklahoma. Note the “tall” eye (eight lenses in most files) that extends close to the ventral margin of the cephalon and the uniform granular surface texture of the head. Specimen 2.6 cm across genals.

Finally it may be helpful to be able to “easily” distinguish Viaphacops from Paciphacops, the two short-eyed genera. In the area of the eye, the clearest way to distinguish these two genera is to compare the height of palpebral area (the region immediately medial to the ocular surface) with the height of palpebral lobe (the roughly triangular region between the palpebral furrow and the glabella). In Paciphacops (and Kainops) the palpebral area is higher than the palpebral lobe. In Viaphacops, the reverse is true (Hansen, 2009). It’s just that simple! (Ha ha!)

Viaphacops, Devonian Period, Oklahoma
Viaphacops, Bois d’Arc Formation, Early Devonian Epoch, Coal County, Oklahoma. Specimen collected and prepared by Bob Carroll. Specimen 2.1 cm across genals.

Reference

Hansen, George P. 2009. Trilobites of Black Cat Mountain. iUniverse, Inc., New York. 404 p.

©2016 Christopher R. Cunningham. All rights reserved. No text or images may be duplicated or distributed without permission.