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Lugo

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1

Mittwoch, 29. April 2015, 10:38

Preparation of a Gerastos sp.

Hi All,

last week i have prepared one of the smaller trilobites that i have still available in my inventory.
I did not take pictures from the intermediate steps, but nevertheless i like to share a few pictures of the finished specimen.
This bugs comes from the Upper Emsian of Zguilma and measures only 1.9 cm.( length )
As you can see there is a pronounced tuberculation on the upper part of the glabella and a rim of smaller tubercles underneath both eyes.
Also on the apex of the occipetal ring sit two tubercles .
Some smaller granulation is visible on the axial part of the thorax and on the pygidium.
Based on these characteristics i am inclined to call this a Gerastos tuberculatus.
But the two genal points of the free cheeks are clearly rounded and i think this eliminates this option.

Even with the work of Gibb and Chatterton, 2010 ( Gerastos from the Lower to Middle Devonian of the southern Moroccan Anti-Atlas region ) at hand, i cannot specify the species name of this trilobite.
Maybe some forum members can help me.

Best regards

Luc
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Michael

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2

Mittwoch, 29. April 2015, 11:21

Hi Luc,

first- as always I can´t help you to give your bug the right name... But it´s a really fine little trilobite, good prepped. I like these little guys, and your Gerastos looks really fine for me. Thank you for showing here !

Greetings
Micha
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Xiphogonium

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Mittwoch, 29. April 2015, 14:05

I will have a look at the Zguilma-Paper by Chatterton et al.
If the trilobite is actually from Zguilma, then there's a chance that it is described and pictured therein.

Mike
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Apianurus

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Mittwoch, 29. April 2015, 15:04

Hallo zusammen,

bisher ist von Zguilma nur eine Gerastos-Art nämlich Gerastos tuberculatus marocensis CHATTERTON et al. 2006 aus dem Ober-Emsium beschrieben worden. Diese Art kommt aber wegen der feineren Tuberkulierung und den den rudimentären Wangenstacheln nicht in Frage. Etwa gleichalt sind Gerastos akrechanus (ALBERTI 1969) und G. rehamnanus (ALBERTI 1969), diese haben aber nichts mit unserer Art zu tun. Ähnlichkeiten scheinen mit Gerastos umerbianus (ALBERTI 1969) oder G. emmetus GIBB & CHATTERRTON 2010 zu bestehen. Allerdings sind beide Arten erheblich jünger. G. umerbianus stammt aus den Crinoidenkalken des Mitteldevons und G. emmetus aus der Bou Dib Formation, mittleres Givetium.

Ulrich

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Mittwoch, 29. April 2015, 16:44

Stimmt, in der Zguilma-Arbeit ist nur der eine Gerastos beschrieben! Die Gerastos-Arbeit von Gibb & Chatterton (Palaeontographica Canadiana No. 30) ist da wirklich ergiebiger.
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Xiphogonium

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Mittwoch, 29. April 2015, 16:55

I just had a look at the trilobite in GIBB & CHATTERTON that Ulrich mentioned, G. emmetus GIBB & CHATTERRTON 2010, and although I am just a layman I agree that it appears to be a close match.
In particular the pointed tubercles on the posterior part of the glabella and the tubercles below the eye socket come very close to your specimen. GIBB & CHATTERTON report them to appear at Taboumahklouft / Issoumour within the Upper to Lower Radiaspis horizon and Droptops megalomanicus horizon.
The genal points and the lateral profile of the cephalon do also appear very much alike.

Source: Gerastos (Order Proetida; Class Trilobita) from the Lower to Middle Devonian of the Southern Moroccan Anti-Atlas region; Stacey GIBB & Brian D. E, CHATTERTON, Palaeontographica Canadiana No. 30, 2010, Plates 20 -23

So the question is whether he information that your specimen comes from Zguilma is verifiable - unless you have collected it yourself there.

Mike
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Mittwoch, 29. April 2015, 18:06

Hi Lugo,

I have to add that the stone looks not realy after typical Zguilma-material and that Zguilma is a closed site since some years, so even so its daubtful that new material from there comes to the light.

I have not yet looked into the Chatterton & Gibb-paper, but Ulrich and Mike have both a kean eye and so you should ask again your source, if there is all alright with the context of that specimen;-)

all the best,
Jens
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Lugo

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Mittwoch, 29. April 2015, 23:24

I thank you all for your input and i fully agree that the description of G. emmetus Gibb and Chatterton 2010 comes by far closest to this specimen.
With the paper of Gibb and Chatterton 2010 at hand this was exactly my problem to find a match between the characteristics of this bug and the enclosed information about the find location.
So now it is clear that i have to doubt about the finding information that was enclosed, when this trilobite was delivered to me in august 2013.
That information mentionned "Gerastos sp. Upper Emsian, Zguilma near Foum Zguid".
Although i am afraid it is now too long ago to trace back more reliable data, i will give it a try.

Best regards

Luc
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Andries

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9

Donnerstag, 30. April 2015, 10:43

Hi Luc,

excellent specimen, I like that small little critter.

Allthough only a small piece of the matrix is visible, neither the matrix or the proetid looks simular to the proetids I have prepped from Zquilma/J'bel Gara/Lansser.

This small bug is from Lansser/J'bel Khraid (or however it's called) and I'm not sure if it has been described already.
Gerastus sp.

Additional here is a prepped Gerastos tuberculatus marocensis
Gerastus

You see, that there are differences between your specimen and the specimens above.
Thus I think that Mike suggestion would be the best guess.
As far as I can tell the matrix would fit.

Best regards,

Andries

Lugo

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Donnerstag, 30. April 2015, 11:57

Hi Andries,

thanks for your comments and clarification.

To all,

this morning i tried to unravel the mystery of this Gerastos and i discovered in my documentation that the box, delivered in august 2013, contained 19 unprepped trilobites. But the corresponding mail listed only 18 specimen. One of these bugs was labeled as Gerastos sp. Upper Emsian, Zguilma near Foum Zguid. I found in my database that i prepped this bug already in september 2013. But because significant fragments of the shell were missing, I never took pictures and i placed this trilobite aside.
This is why i mistakenly assigned again the Zguilma location to the bug ( clearly also a Gerastos ) of the august 2013 delivery, that i prepped last week. This bug was not listed and was clearly extra in the box.

I have now taken a few pictures of the trilobite ( see below ), prepared in september 2013 and i think this is a Gerastos tuberculatus marocensis Chatterton and al. 2006.

Thanks to the expert comments from you all my mistake came to the surface and part of the mystery is solved.
The next step is now to find the digging information of this" extra" Gerastos, ( Gerastos emmetus Gibb and Chatterton, 2010 or still something else?) that was sitting in the box.

Best regards

Luc
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ikkes

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Samstag, 2. Mai 2015, 21:22

Klein maar fijn!!

And again nice prep work.

Lugo

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Dienstag, 12. Mai 2015, 13:49

I received this morning from my Moroccan contact the missing digging information of the Gerastos sp. that i presented in this thread.
The findlocation is the Eifelian ( more specific the Ceratarges couche) from Jebel Serdrar.
I am not familiar with this location, which is located more nord than the typical digging trenches in the Mader basin.

Best regards

Luc
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Jens

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Dienstag, 12. Mai 2015, 14:09

Hi Lugo,

I had the same feeling when I was looking at the matrix, but I hesitated to ask again if the location information is right. The site of the Jebel Serdrar is close situated to Tazzarine and finds of Gerastos and Cornuproetus are common. The occurrence of Septimopeltis and Ceratarges suggest me an age of the Middle Eifelian. However, I looked into the Chatterton & Gibb-paper some days ago to look if there is Serdrar-material in it. And yes, it is, a species called Gerastos hammii, which I would believe is from the same layer. Chatterton & Gibb wrote Saredrar as location name, as always we find different spellings. But the Gerastos in that paper has lang genal spines, so I excluded it as a possible determination and was less sure that Lugo's specimen is from that site.

I have some own specimens from there by my own, but not prepared yet. If I find some time I can look if they can be compared. The lithology is similar but I haven't seen such narrow spaced fractures from that site. But who knows, might be that it is only a local phenomen there.

PS: What I wrote here is more thought for the other specimen you showed, with the associated head. However, G. hammi did not fit for both;-) I got confused that the other Gerastos-thread was on top.

all the best,
Jens
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Lugo

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Donnerstag, 14. Mai 2015, 16:34

Hi Jens,

it is indeed a bit confusing by having these twee Gerastos posting next to each other. Sorry for that.

But it gets even more confusing when i try to understand the findlocation.
The Gerastos hammii digging location mentioned in Gibb and Chatterton is indeed Saredrar ( at 30° 45' 24.6'' N and 5° 27' 39" W ), but the information i got from my local supplier for the Gerastos showed at the beginning of this posting says Eifelian ( Ceratarges couche ) at Jebel Serdrar. And i found this mountain on Google Earth at 32° 00' 36'' N and 4° 55' 36'' W., north of the Mader basin. I have no idea if this place ( at about 1400 m altitude ) is also known as a trilobite digging location or not.

Best regards

Luc
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Lugo

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Freitag, 15. Mai 2015, 18:03

I got now confirmation that the findlocation is Saredrar, close to the town of Tazzarine; so we can forget Jebel Serdrar.

Best regards

Luc
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