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The popular collected trilobite Phacops rana is well embedded in literature for over a hundred years. Then in 1990 it was renamed Eldredgeops rana. A lot of collectors did not understand why the name change and I would like to attempt to clarify why the change.

The purpose of this post is to point out the differences I have observed between Phacops and Eldredgeops and explain why "rana" is an Eldredgeops and not a Phacops. The literature on phacopid systematics is in a mild state of disarray. Authors have built on the errors of previous authors. There is no good English diagnostic description of Phacops based on the type species of P. latifrons. This has resulted in different English definitions of Phacops and causing much confusion. I'll first start with a review of what are the types and where they come from.
Types:
1. Phacops
Emmrich (1839) described the genus Phacops based on the species Calymmene latifrons Bronn, 1825 from the Middle Devonian (Eifelian Junkerberg Formation), Gerolstein, Germany.
Because the holotype has been lost, it has not been clear what to base the diagnosis of Phacops on over many years. Then Struve (1982) illustrated topotype material but it was Basse (2006) who designated the neotype of Phacops latifrons. Now there is a definitive specimen to base the description of Phacops on.

I have been fortunate to have traded for a topotype cephalon of Phacops latifrons
Definition of topotype - a specimen of a species collected at the locality at which the original type was obtained

2. Eldredgeops
Stewart
(1927) described Phacops rana milleri from the Middle Devonian (Givetian Silica Shale), Sylvania, Ohio.
Struve (1990) designated Phacops rana milleri the type species of Eldredgeops.

I believe the different subspecies of Phacops rana described by Eldredge (1972) are different species and are assigned to Eldredgeops. I will to refer to these different species Eldredgeops as the "rana group" as a way to simplify the naming of all the different species.


Observed different characters:

I do not know what are the diagnostic generic features of Phacops or Eldredgeops. All I'm doing is listing some of the differences I have observed between these two trilobites to show they are different genera.

Pictures of Phacops latifrons and Eldredgeops milleri are below for comparison with numbers pointing to the different features. Pictures of Eldredgeops rana from New York are also included so one can compare the two species of Eldredgeops and see how they differ.

Now for the first time a topotype specimen of Phacops latifrons is compared with a topotype specimen of Eldredgeops milleri. There is no place in the literature where this is done.


1) marginulation - a raised ridge along the ventral margin of the cephalon.
It is present in the "rana group" and absent in P. latifrons. It has been used by Flick and Struve (1984) as a diagnostic feature for their tribe Geesopini.
Note: The value of this feature for the tribe has been questioned. McKellar and Chatterton (2009) state "This feature has never really been evaluated from a phylogenetic standpoint"
2) The post ocular ridge is prominent in P. latifrons and is absent in the "rana group"
3) The
palpebral area is smaller in P. latifrons than in the "rana group"
4)
The palpebral lobe is smaller in P. latifrons than in the "rana group"
5) The number of eye files in the "rana group" ranges from 15-18.
E. milleri has 18 and E. rana has 17. In P. latifrons the number of eye files is 14-15. The topotype specimen has15 files with a maximum number of 5 lenes.
6) The maximum number of lenes in
P. latifrons is between 4-5; E. milleri has 8-9; E. crassituberculata has 6 or less; E. rana 6
Note: Both P. latifrons and E. norwoodensis from the Cedar Vally Formation have the same number of files (15) in the eye. One might determine that this would result in the palpebral lobe being the same size but this does not happen. P. latifrons is smaller than E. norwoodensis. So there is some other factor affecting the size of the palpebral lobe.
7) The subocular pad is present in
P. latifrons and absent in the "rana group"
8)
The glabella is inflated and its front wall varies from vertical to slightly overhanging the anterior border in the "rana group" and is not as inflated in P. latifrons
9) Lateral preoccipital lobe is round in P. latifrons and is rectangular in Eldredgeops.

To summarize the differences:
Eldredgeops
is
marginulated, has an inflated glabella, a rectangular lateral preoccipital lobe, the palpebral area and palpebral lobe are larger than
P. latifrons, and does not have a post ocular ridge and subocular pad.
Phacops latifrons is not marginulated and the glabella is not inflated, has a post ocular ridge and a subocular pad and a round lateral preoccipital lobe. the palpebral area and palpebral lobe are smaller than Eldredgeops.

Other observations:

These two genera occur in different time periods.
Phacops latifrons is in Middle Devonian Eifelian and Eldredgeops milleri is in the Middle Devonian Givetian

It appears all the phacopid of North America disappear at the end of the Eifelian and Eldredgeops migrates from the Old World fauna into North America in the Givetian. Eldredgeops does not evolve from any North American phacopid.

Eldredgeops is in the Tribe Geesopini and all the genera of this tribe have not been validated. If these genera are reexamined, it is possible that Eldredgeops could become a junior objective synonym of an another genus in the Tribe Geesopini.

Hopefully, now collectors will understand the differences between
Phacops and Eldredgeops and why the "rana" group is now referred to as Eldredgeops.

Phacops-3 copy.jpgPhacops-10 copy.jpgPhacops-2.jpg

E. milleri -1.jpgE. milleri -2.jpgE. milleri -3.jpg

E. crass.jpgPhacops-7 copy.jpgPhacops-8.jpg

Phacops-6 copy.jpgPhacops-4.jpgPhacops-5.jpg

  • I found this Informative 45
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Jesuslover340

Thank you very much! I learned quite a bit from this post! :)

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Northern Sharks

Great post Gerry. Very informative

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Great analysis and images, Gerry. Your topic has been Pinned.

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Ok, now that I can SEE the differences and understand why the names are different I think I may be on board the Eldredgeops bandwagon. Thank you for putting this together. Did you modify the pictures so that all the specimens had the same color and tone? That certainly makes a difference.

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Ok, now that I can SEE the differences and understand why the names are different I think I may be on board the Eldredgeops bandwagon. Thank you for putting this together. Did you modify the pictures so that all the specimens had the same color and tone? That certainly makes a difference.

I coated the trilobites white with ammonium chloride to increase the contrast. The blue color is do to the lighting and camera

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The labels in my display case seem to be in order. ;) Thank you for taking the time to post this Gerry. I'm glad to see clarification on why my favorite trilobite changed his name.

mikey

post-7129-0-90061000-1402349548_thumb.jpg

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Thanks for this Gerry. I just accepted the change in name without really going into it deeply, but now I can see and understand the difference.

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Thanks for this, one of the best posts on the forum.... Now to start going through all my Eldredgeops to see what exactly I have

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The labels in my display case seem to be in order. ;) Thank you for taking the time to post this Gerry. I'm glad to see clarification on why my favorite trilobite changed his name.

mikey

The name change of Phacops rana to Eldredgeops rana may not be the end of the story. At the fossil picnic I showed you Basse's (2006) monograph on the phacopids, there were a lot of genera you could see in the tribe Geesopini that look like "rara." A revision of the Geesopini could result in Eldredgeops becoming a junior objective synonym of an another genus and have another name change.

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  • 3 weeks later...

Wow, excellent post! Also there is a difference not just in the inflation (or rise) of the glabella, but the articulation whereby Phacops has a distinctive "big pores" aspect. Also of note is the relation between the thorax segments and the cephalon. Note how the thoracic section extends into the cephalon region between the E. Millert and E. Rana. Were there any distinct differences in pygidia?

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  • 1 month later...

Thanks for posting this, very informative :)

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I coated the trilobites white with ammonium chloride to increase the contrast. The blue color is do to the lighting and camera

Is the coating permanent?

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Is the coating permanent?

Not at all; it dusts right off.

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  • 6 months later...
Carcharomimus

Very interesting! That helped me, I was also confused about phacops and eldregeops, but from your picture I'm happy to now being able to confirm that my trilobite cephalons are from eldregeops ( rana crassituberculata?), as it was identified when I bough them! From lucas county Ohio

I have a small fossil consisting of two eldregeops cephalons on the same rock, very close from each other, and one is huge, the other is only the size of the eye of the big one! Honestly, I think I can't see what make it different from eldregeops milleri, they share so much similarities, well for my eye at least hehe.

post-17801-0-21421600-1426172830_thumb.jpg

Edited by Carcharomimus
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  • 3 months later...

My compliments for this post, you nailed it! Good to see some of the valuable german language literature featured here.

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  • 1 month later...

Thanks JohnJ for pinning this. I would not have seen it otherwise.

GerryK, this post makes all the difference. Kudos! (and thanks)

Edited by billheim
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  • 2 months later...
  • 5 weeks later...

Great post! Thank you for taking the time to add it!!

Question: In looking at the Phacops I have on hand, can you clarify what a "file" is when referring to the eyes? I assume row? but in what direction is the grouping made to form a file? Or am I totally off on this?

Edited by BrokenTrowel
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Great post! Thank you for taking the time to add it!!

Question: In looking at the Phacops I have on hand, can you clarify what a "file" is when referring to the eyes? I assume row? but in what direction is the grouping made to form a file? Or am I totally off on this?

A file is a vertical row of lenses. In the picture below a file is out lined in red

post-7992-0-45696300-1448816639_thumb.jpg

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  • 1 year later...

Gerry, the middle line of 3 photos marked as E. milleri are actually 3 photos of E. crassituberculata.  What were formerly the two subspecies of P. rana became species level to Eldredgeops per Struve. 

milleri or crassi.jpg

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  • 6 months later...
Reese the Rockhound

Would anyone happen to know if both Phacops and Eldredgeops can be found at Penn Dixie FP, or just Eldregeops?

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