Flat fish from Ordovician

[Dimitar]

The previous picture is rotated at 180 degree.  Same picture with the correct angle of view:

 

The exoskeleton is preserved and visible.  Here on this picture I hope it is a lot better visible as bumps.

[Top Trilo]

I am not sure what your question is. It is a mold/negative of a Amphilichas trilobite as Kane and others pointed out. Many negatives have the same color as the positive.

[piranha]

Amphilichas minganensis is also reported from Laval.  The pygidial axial furrows have a narrower termination on A. minganensis and A. ottawaensis.

 

[Kane]

I didn't think A. minganensis ventured that far west! Very cool! My sources don't list anything other than A. ottawaensis so I must be addled with older literature. Let me know if you have some Laval goodies in terms of lit to share!

[piranha]

 

Clark, T.H. 1952
La Région de Montréal Feuilles de Laval et de Lachine. [The Montreal Region Laval and Lachine Sheets.]

Province de Québec, Canada Ministère des Mines, Rapport Géologique, 46:1-150  PDF LINK

[Kane]

Downloaded. It's odd I didn't have this one already. A godsend as always. 

[Fossildude19]

Ah. This makes it very confusing, being a high contrast image. Still, it is a trilobite exoskeleton.

[piranha]

After a deep dive into the literature...  I finally found the pygidium with the matching postaxial band.

 

Amphilichas welleri (Foerste 1920)

 

Foerste, A.F. 1920

The Generic Relations of the American Ordovician Lichadidae. American Journal of Science, Series 4, 49:26-50

[Kane]

On 4/23/2021 at 7:18 PM, Thomas.Dodson said:

I wouldn’t argue trilobites against Kane, he knows his stuff. 

I certainly know my backyard, but I remain a shadow to @piranha’s expertise. At best, I got the genus right. We can at least rule out other genera at this point.

[Dimitar]

Do you think I should register this specimen? Please advise.

[Mahnmut]

Hi Dimitar

Imagine a crab or insect with a nicely structured shell, that is what you got there, thats what exoskeleton means. But a really nice fossil.

Best Regards,

J

[Kane]

12 hours ago, Dimitar said:

Do you think I should register this specimen? Please advise.

I'm not sure what you mean by "register" but you can always donate the specimen if it has scientific value. 

 

One of your nearest repositories would be Musée de paléontologie et de l'évolution. You'll want to talk with Mario who curates the collection. If it is deemed of scientific value, he would issue you a tax receipt.

[piranha]

After some additional searching there seems to be a possibility of synonymous taxa. Amphilichas welleri (Foerste 1920) was based on a single pygidium from the Kimmswick Limestone of Cape Girardeau, Missouri. No formal description was given and subsequently (Bradley 1930) established a new species Amphilichas aspratilis, with only a brief mention that Foerste thought A. welleri might represent an aberrant form of A. cucullus. Chatterton & Ludvigsen 1976 described Amphilichas aff. A. aspratilis from the Esbataottine Formation, Northwest Territories, Canada. Unfortunately the figured pygidia are fragmentary but appear to be similar enough to warrant additional investigation. I have forwarded the photos to a lichid specialist friend for further clarification. Stay tuned!

 

 

Bradley, J.H. 1930

Fauna of the Kimmswick Limestone of Missouri and Illinois. Walker Museum, Contributions, 2(6):219-290

 

Chatterton, B.D.E., Ludvigsen, R. 1976

Silicified Middle Ordovician Trilobites from the South Nahanni River Area, District of Mackenzie, Canada. Palaeontographica Abt.A 154:1-106

[Dimitar]

 

[Kane]

Keep us posted @piranha -- you're a real treasure around here!

[piranha]

@Dimitar

 

In your initial post you stated: "Found in shale block - mud stone  Between Montreal and Laval"

 

Are you the person that actually field collected this specimen in the vicinity of Montreal / Laval?  Or by chance, did you acquire it by other means?

[Dimitar]

25 minutes ago, piranha said:

@Dimitar

 

In your initial post you stated: "Found in shale block - mud stone  Between Montreal and Laval"

 

Are you the person that actually field collected this specimen in the vicinity of Montreal / Laval?  Or by chance, did you acquire it by other means?

yes, I found it. I almost took it from the mud, from the river.   

If ther river is high, it goes over the place.  If the river is low, it is accessible at some time. 

Just to clarify: I found it the last Summer.

Edited April 25, 2021 by Dimitar

[piranha]

The lichid specialist replied that key diagnostic features suggest this is not Amphilichas. Apart from the shape of the postaxial band, the notch between the second and third marginal spines shown on the right side of the specimen appears broad and rather rounded, not an acute angle as in Amphilichas.  With the assistance of a skilled preparator it may be possible to expose more of the pleural margins that could lead to a more conclusive ID. You should also attempt to revisit the locality to collect some additional specimens. In the meantime, this unusual fragmentary pygidium can only be classified as an indeterminate 'tetralichine' lichid.

 

Carlucci, J.R., Westrop, S.R., Amati, L. 2010

Tetralichine Trilobites from the Upper Ordovician of Oklahoma and Virginia and Phylogenetic Systematics of the Tetralichini. Journal of Paleontology, 84(6):1099-1120

[Dimitar]

I found another one today. But unfortunately the quality if it was so bad, that I am even afrait to share it with you.  On the other side - it was the full body of it.  And I took it from both side - bottom and top.  It is smaller - near 5 cm long.   It is impossible to recognize such thing, unless if someone is looking specially for it. 

 

 

These are both sides: I found it because of the color.  Unfortunately this color is changing fast on the air, and this rock is from mud. So it can't stay stable for long time, it start to desintegrate.

 

 

 

Below I attempt to reconstruct what is the trilobite here. 

 

 

 

 

There is a small piece from the pleural spines, that desintegreated: 

 

 

Edited April 26, 2021 by Dimitar

[Misha]

I do not see any evidence of a trilobite there, the color is probably there due to a different mineral on the surface of the matrix.

Also the shape that you outlined looks nothing like any trilobites I am familiar with.

[Dimitar]

27 minutes ago, Misha said:

I do not see any evidence of a trilobite there, the color is probably there due to a different mineral on the surface of the matrix.

Also the shape that you outlined looks nothing like any trilobites I am familiar with.

Ya, you seems to be right! I did other pictures - it may be the roots of some tree, because it is not too deep. 

 

[Kane]

It is doubtful you'll be encountering Ordovician trees. 

[Dimitar]

4 hours ago, Kane said:

It is doubtful you'll be encountering Ordovician trees. 

The tree roots are very late, and recent. Because this rocks are less than 1m from the serfice now - there are trees around.. Some roots are recent, some are ancient.  The mud and rocks there are soft, so it allows some roots to go deeper through the cracks.

 

The place is near the river, so there is lot of erosion because if it. These rocks crack and dissolve in the water.

Edited April 26, 2021 by Dimitar

[Dimitar]

I looked at it again - it is not root of a tree. It is some yellow sand, covered by a thin layer of cemented sediments. On top of it is another softer layer of mud (stone). Because of all these different materials  I was confused by some paralel lines and holes.. Finally - it is nothing there.  Just some geological processes.   Thank you guys!