Kosmoceras (?) ammonites from Khakassia, Russia

[Ailanna]

I recently bought these two ammonites from a seller who listed them as Kosmoceras sp from Khakassia, Russia, Jurassic period. Based on shape and size, I think these are likely the same species, but the white one has had more shell material removed; what's remaining looks super chalky with a lot of calcium in it. The more intact fossil has curvy ribbing and a slightly braided look to the keel, which has a distinct bevel. 

 

I haven't ever seen a Kosmoceras that looks like this - my other Kosmoceras specimens are pyritized fossils from near the Volga River and look much spinier. Can anyone confirm the ID or suggest a different one? Thank you!

[Mark Kmiecik]

The genus Kosmoceras includes more than 100 species. I'm thinking that may account for some variation in what is found at a particular location especially from different strata.

[Ludwigia]

If these are Kosmoceras, then they certainly look a lot different than what I'm used to seeing. They generally have ornately sculptured ribs, sometimes with spines and the keel usually has a furrow. Your specimens show none of these traits, which leads me to believe that you have another genus, although I'm not at all sure what they might be without more precise stratigraphic information. I tried a google search for Khakassian ammonites, but it brought nothing but a few links to the same seller with the same ammonites as yours.

[Ailanna]

2 hours ago, Ludwigia said:

If these are Kosmoceras, then they certainly look a lot different than what I'm used to seeing. They generally have ornately sculptured ribs, sometimes with spines and the keel usually has a furrow. Your specimens show none of these traits, which leads me to believe that you have another genus, although I'm not at all sure what they might be without more precise stratigraphic information. I tried a google search for Khakassian ammonites, but it brought nothing but a few links to the same seller with the same ammonites as yours.

Thank you for your expert opinion! I'm inclined to agree that this is not a Kosmoceras. In addition to the pyrite ones, I have a Kosmoceras from England (formerly Guliemiceras) that shares the sculpted ribs and furrowed keel. Since ammonite taxonomy is mostly based on morphology, I'd expect to see at least some shared characteristics in a congeneric species. I bought these out of novelty - hey! not a Cleoniceras! - but finding any solid information on them is proving daunting.

[Ludwigia]

7 hours ago, Ailanna said:

Thank you for your expert opinion! I'm inclined to agree that this is not a Kosmoceras. In addition to the pyrite ones, I have a Kosmoceras from England (formerly Guliemiceras) that shares the sculpted ribs and furrowed keel. Since ammonite taxonomy is mostly based on morphology, I'd expect to see at least some shared characteristics in a congeneric species. I bought these out of novelty - hey! not a Cleoniceras! - but finding any solid information on them is proving daunting.

Well, good luck to ya. Maybe someone at one of your museums can help you further. I have the feeling that the given provenance is also not correct.