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RuMert

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On 10.06.2020 at 9:33 AM, caterpillar said:

Sorry but it's not a Plegiocidaris

What do you think it is? The definition I got on the local forum is "conditionally classified as Plegiocidaris"

Guides/handbooks on Moscow Mezozoic (unfortunately mostly outdated) list 5 genera: Echinobrissus, Rhabdocidaris, Acrocidaris, Holectypus and Cidaris. For this and neighboring stratigraphic zones Echinobrissus and Rhabdocidaris only, mainly the latter. Both are defined by spines, sometimes isolated plates

IMG_20200602_134724.jpg

IMG_20200602_135241.jpg

IMG_20200602_135309.jpg

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I do not know what it is because it is too eroded. We do not see if the tubercules are perforated, crenulated. But what is certain is that it is not an Echinobrissus, Rhabdocidaris, Acrocidaris, Holectypus or Cidaris. Look at the ambulacral zones. They are composed of 2 rows of pores. Cidarids are not like that.
Are you sure it comes from the Moscow Tithonian?
 
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I extracted it from a Dorsoplanites panderi zone concretion. Found it myself on surface, not in the layer, but occurence of other zone's concretions is basically excluded and the preservation is typical for the zone. Here's a similar echinoid from a neghiboring region. Unfortunately I'm by no means a specialist on echinoids:headscratch:

There are too many undescribed species and I guess it's more likely than someone dropping a concretion they found somewhere else (taking into consideration its typical preservation again). The corresponding trip report is here

 

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There are 2 large families of sea urchins. Regular sea urchins and irregular sea urchins.
The sea urchin you show me as a link is a Holectypus, an irregular sea urchin.
The one you found is a regular sea urchin.
It is absolutely not the same thing. It's like you're comparing a lizard and a cow. Yes they are both vertebrates but they have nothing to do with each other.
Your sea urchin could be a Loriola but it is too damaged to be sure
 

 

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@RuMert

 

I have split this discussion out of the June FOTM topic to better facilitate an identification.  Could you please upload the echinoid images here.  Also, please include an image of the "bottom", not seen in the other topic.  Thank you, sir.  :)

 

@caterpillar

The human mind has the ability to believe anything is true.  -  JJ

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2 minutes ago, RuMert said:

Thank you, I hope so. I'll try to take more pictures and maybe find the exact concretion it came from

 

If you can get a photo of the side touching the wire, it might help.  ;)

The human mind has the ability to believe anything is true.  -  JJ

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Yep, I found the picture, but it's not clear - covered with parts of the concretion. Unfortunately the matrix is tough and the test remains are fragile, I wouldn't like to end up with a black steinkern

 

IMG_20200602_134228.jpg

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@RuMert  Thank you.  This is the apical side of the echinoid.  

 

The first photo in this topic is of the oral side (bottom) of the echinoid.  This is indicated by the gill slits (small notches) still evident in the margin of the peristome (mouth).  

 

 

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The human mind has the ability to believe anything is true.  -  JJ

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OK, thank you:tiphat: I'll look into the guides again and discuss locally. Unfortunately fossil echinoids are much less studied here compared to ammonites, for example. I'll post what I find

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I agree that this sea urchin no longer shows the distinctive signs to recognize a species.

 

Coco

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----------------------
OUTIL POUR MESURER VOS FOSSILES : ici

Ma bibliothèque PDF 1 (Poissons et sélaciens récents & fossiles) : ici
Ma bibliothèque PDF 2 (Animaux vivants - sans poissons ni sélaciens) : ici
Mâchoires sélaciennes récentes : ici
Hétérodontiques et sélaciens : ici
Oeufs sélaciens récents : ici
Otolithes de poissons récents ! ici

Un Greg...

Badges-IPFOTH.jpg.f4a8635cda47a3cc506743a8aabce700.jpg Badges-MOTM.jpg.461001e1a9db5dc29ca1c07a041a1a86.jpg

 

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This echinoid classification is not a simple thing:headscratch:I had no idea the echinoid on that linked picture was irregular (it looks round), while mine, which doesn't look to have a five-fold symmetry, is a regular one. Again, we are not used to echinoid tests, they are somehow not preserved at all. I posted my specimen not as the best of the 500 echinoids I have, but simply because they are too rare in the region and everybody would be excited to find one whatever the preservation. Below are the species known in the Moscow Tithonian (by zone)

 

1123.jpg

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It can be complicated by the level of preservation.  The one in the link would be obvious if you could see the bottom.  ;)

 

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The human mind has the ability to believe anything is true.  -  JJ

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We can all agree that things can be confused in translation.  Let's continue this topic politely. 

The human mind has the ability to believe anything is true.  -  JJ

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